Research Articlen-Hexadecane Fuel for a Phosphoric Acid DirectHydrocarbon Fuel Cell
Yuanchen Zhu12 Travis Robinson1 Amani Al-Othman23
Andreacute Y Tremblay1 and Marten Ternan4
1Chemical and Biological Engineering University of Ottawa 161 Louis Pasteur Ottawa ON Canada K1N 6N52Catalysis Centre for Research and Innovation University of Ottawa 30 Marie Curie Ottawa ON Canada K1N 6N53Chemical Engineering American University of Sharjah Sharjah UAE4EnPross Incorporated 147 Banning Road Ottawa ON Canada K2L 1C5
Correspondence should be addressed to Marten Ternan ternanbellnet
Received 8 January 2015 Accepted 17 March 2015
Academic Editor Michele Gambino
Copyright copy 2015 Yuanchen Zhu et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The objective of this work was to examine fuel cells as a possible alternative to the diesel fuel engines currently used in railwaylocomotives thereby decreasing air emissions from the railway transportation sector We have investigated the performance of aphosphoric acid fuel cell (PAFC) reactor with n-hexadecane C
16H34(amodel compound for diesel fuel cetane number = 100)This
is the first extensive study reported in the literature in which n-hexadecane is used directly as the fuel Measurements were madeto obtain both polarization curves and time-on-stream results Because deactivation was observed hydrogen polarization curveswere measured before and after n-hexadecane experiments to determine the extent of deactivation of the membrane electrodeassembly (MEA) By feeding water-only (no fuel) to the fuel cell anode the deactivated MEAs could be regenerated One set of fuelcell operating conditions that produced a steady-state was identified Identification of steady-state conditions is significant becauseit demonstrates that stable fuel cell operation is technically feasible when operating a PAFC with n-hexadecane fuel
1 Introduction
Fuel cells offer many advantages for the conversion of thechemical energy in a fuel into electrical energy Fuel cellenergy efficiencies can be greater than those of conventionalcombustion engines For example because Carnot heatengines are limited to the maximum temperature that theirmaterials can withstand their theoretical energy efficiencyis close to 67 In contrast fuel cells do not have materialslimitations and can have larger theoretical energy efficienciesOften emissions from fuel cells are generally less than thosefrom combustion engines In some applications fuel cells arecompeting successfully with batteries in part because theycan use fuel continuously whereas batteries stop providingelectrical power as soon as their charge has been exhausted
Fossil fuels are usually the lowest cost source of energyand that is not apt to change in the foreseeable futureUnfortunately emissions from fossil fuels have a negative
effect on the earthrsquos climate Direct hydrocarbon fuel cells(DHFCs) can have theoretical energy efficiencies near 95Their large energy efficiencies mean that a smaller quantity offuel is required and therefore they will emit fewer emissionsand have a smaller impact on climate change than heatengines or themore technological advanced fuel cells that usehydrogen or methanol as their fuels
Thepurpose of thisworkwas to decrease both greenhousegas emissions (CO
2 CH4 and N
2O) and air contaminants
(NO119883 CO HC and SO
119883) by replacing locomotive diesel
engines with fuel cell engines n-Hexadecane (cetane num-ber = 100) was used as a model compound to representcommercial diesel fuels A phosphoric acid fuel cell wasused because its temperature is high enough to ensurethat the n-hexadecane would be in the vapour phase if anappropriate steamn-hexadecane ratio is used Therefore theexistence of two liquid phases within the fuel cell could beavoided
Hindawi Publishing CorporationJournal of FuelsVolume 2015 Article ID 748679 9 pageshttpdxdoiorg1011552015748679
2 Journal of Fuels
Direct hydrocarbon fuel cells have other advantagesDHFC systems have lower capital costs than other fuelcell systems because the fuel processing systems (steamreforming etc) for hydrogen and methanol fuels are notrequired In addition the infrastructure already exists fordiesel fuel and other petroleum derived fuels That is not thecase for hydrogen or methanol fuels Storage of liquid fuelssuch as diesel fuel ismuch easier than storage of gaseous fuelssuch as hydrogen
Unfortunately DHFCs have one major disadvantageTheir current densities are much smaller than those ofhydrogen and methanol fuel cells Work in our laboratory isbeing performed to understand the characteristics of DHFCswith a long-term objective of improving their performance
William Grove demonstrated the first fuel cell operationin 1839 using hydrogen as the fuel He was also creditedwith suggesting possible commercial opportunities if coalwood or other combustibles could replace hydrogen [1]which would be DHFCs Direct hydrocarbon fuel cells wereinvestigated intensely in the 1960s Three reviews of theDHFC work up to that time are available [2ndash4]
Research on DHFCs has continued Low-temperaturefuel cell studies (lt100∘C) were performed on methane byBertholet [5] and on propane by Cheng et al [6] andby Savadogo and Rodriguez Varela [7 8] Heo et al [9]performed intermediate temperature fuel cell studies (100ndash300∘C) using propane A larger number of DHFC studieshave been performed on solid oxide fuel cells Studies usinglow molecular weight hydrocarbons frommethane to butanewere performed by Steele et al [10] Murray et al [11] Zhu etal [12] Gross et al [13] and Lee et al [14] Larger moleculeswere studied by Ding et al [15] (octane) Kishimoto et al [16](n-dodecane) and Zhou et al [17] (jet fuel) Our own workhas focused on modeling the fuel cell reactor [18ndash20] mod-eling the fuel cell catalyst [21ndash23] experimental developmentof an electrolyte that is appropriate for temperatures abovethe boiling point of water [24ndash26] and experimental fuel cellstudies [27 28]
Phosphoric acid fuel cell systems have an extensivedevelopment history A 250ndash400 kW fuel cell system toproduce stationary electric power was developed by Prattand WhitneyONSIUTC Power 300 units were built in19 different countries The company was sold to ClearEdgePower and was recently acquired by Doosan Industries Thephosphoric acid fuel cell technology has been documentedextensively [29ndash32]
The fuel in this work was n-hexadecane There were onlythree data points reported previously in a fuel cell study thatexamined a variety of fuels [33] This is the first fuel cellstudy devoted exclusively to n-hexadecane In a direct n-hexadecane phosphoric acid fuel cell the overall reaction is
C16H34(g) + 492
O2(g) 997888rarr 16CO
2(g) + 17H
2O (g) (1)
The anode half-cell reaction is
C16H34(g) + 32H
2O (g) 997888rarr 16CO
2(g) + 98H+ + 98eminus
(2)
The cathode half-cell reaction is49
2
O2(g) + 98H+ + 98eminus 997888rarr 49H
2O (g) (3)
where the (g) represents the gas phase The anode stoi-chiometric ratio SR = H
2OC16H34
is 32 One mole of n-hexadecane reacts with 32 moles of water at the anode andgenerates 98 moles of protons and electrons The protonsmigrate through the electrolyte to the cathode where theoxygen reduction reaction occurs
Bagotzky et al [34] described a reaction mechanism fordirect hydrocarbon fuel cells using methane as a feedstockThe Bagotskymechanismwasmodified as shown in Figure 1to describe n-hexadecane The desired product is CO
2
However alcohols aldehydes carboxylic acids and lowermolecular weight hydrocarbons are possible by-productsThree reactions are shown in Figure 1 dehydrogenation (fromboth carbon and oxygen atoms) hydroxylation and CndashCbond cleavage Two reactions are not shown water dissoci-ation (H
2O rarr H + OH) and hydrogen atom ionization
(H rarr H+ + eminus) Hydrogen ionization is an electrochemicalreaction and therefore is influenced by potential The otherfour reactions are chemical reactions and are not influencedby potential
The objective of the work described here was to identify aset of operating conditions that would permit stable contin-uous operation of a direct hydrocarbon phosphoric acid fuelcell using n-hexadecane as the fuel
2 Experimental
A schematic diagram of the direct n-hexadecane fueledphosphoric acid fuel cell (PAFC) system is shown in Figure 2The overall system consists of an air cylinder a hydrogencylinder one Galvanostat two syringe pumps a vaporizera phosphoric acid fuel cell (PAFC = Electrochem FC-25-02MA) and a fuel cell test station Both gaseous and liquidfuels can be used in this fuel cell system Deionized waterand n-hexadecane were introduced into the vaporizer by thesyringe pumps The liquid fuels were expected to vaporizebefore reaching the anode of the fuel cell Air was fed to thecathode at a constant flow rate On those occasions whenhydrogen was used as the fuel the pumps were stopped andthe valve in Figure 2 was opened
The membrane electrode assembly (MEA) used in ourfuel cell work had five layers two gas diffusion layers (GDL)two catalyst layers (CL) and a liquid electrolyte layerThe gasdiffusion layers were Teflon coated Toray paper
The liquid electrolyte was initially 85 (146M) phos-phoric acid which was held in a SiC matrix between theanode and cathode catalyst layers Platinum (05mg Ptcm2)supported on carbon (10 Pt on C) was the catalyst in bothanode and cathode catalyst layers The fuel cells had a facearea of 25 cm2 A pin-type flow field was machined in agraphite plate The current collectors were sheets of coppermetal that had been gold plated on both sides Silicone rubberflexible heaters were attached to each current collector
Several types of experiments were performed Hydrogenpolarization curves were measured to determine the state
Figure 1 Diagram of a modified Bagotsky anode reaction mechanism H(CH2)119873CH3= hexadecane if119873 = 15 +OH = Hydroxylation minusH =
Dehydrogenation and bc = CndashC bond cleavage Two reactions are not shown water dissociation H2O = H + OH and the electrochemical
reaction H = H+ + eminus
Flowmeter
Air H2
n-Hexadecane
Deionized H2O
Syringe pumps
AD converter
Vaporizer
Galvanostat
Ano
de
Elec
troly
te
Cath
ode
Fume hood
Condensate
Computer
Figure 2 Diagram of a direct n-hexadecane fueled phosphoric acid fuel cell system
of the MEA in the fuel cell A polarization curve showsthe potential difference as a function of current density n-Hexadecane polarization curves were measured Two typesof time-on-stream experiments were performed (H
2O with
n-C16H34
and H2O only) The time-on-stream experiments
were performed at (a) different molar ratios of water to n-hexadecane (b) different current densities and (c) differenttemperatures
The following operating conditions were used Sepa-rate syringe pumps were used to feed both water and n-hexadecane The water flow rate was expressed as a functionof the stoichiometric ratio (SR) of H
2OC16H34
in (2) for
the anode half reaction A constant flow rate of n-hexadecane(02mLh) was used in all experiments The two water flowrates and their stoichiometric ratios were 1mLh (25 lowast SRH2OC16H34
= 80) and 51mLh (129 lowast SR H2OC16H34
=414) Some experiments were performed with only waterbeing fed to the fuel cell The experiments were performedat two temperatures 160∘C and 190∘C
A Hokuto Denko HA-301 Galvanostat was used to adjustthe potential difference between the anode and cathode of thephosphoric acid fuel cell to maintain the chosen current at aconstant value The potential difference was recorded everysecond using a Lab View data logger
4 Journal of Fuels
0010203040506070809
1
0 05 1 15 2 25 3 35 4 45
Pote
ntia
l diff
eren
ce (V
)
New MEA
Reference
Current density (mAcm2)
Figure 3 Polarization curve for a hydrogen fueled PAFC poten-tial difference between the electrodes (Volts) and current density(mAcm2) Open diamonds are data obtained on a newMEA Opensquares are data obtained on an MEA that had been conditionedin previous experiments with low molecular weight hydrocarbons(ethylene propane) Anode hydrogen flow rate = 96mLh Cath-ode air flow rate = 245mLmin Temperature = 160∘C Pressure =1 atm
3 Results and Discussion
Two hydrogenair polarization curves obtained with a PAFCare shown in Figure 3 The upper curve was the firstexperiment performed with a new MEA The lower curvewas measured after some conditioning experiments hadbeen performed with low molecular weight hydrocarbons(ethylene propane) It is an indication of the condition ofthe MEA at the beginning of this investigation and will bereferred to as the Reference polarization curve The opencircuit potential in Figure 3 is about 093V It is comparableto the 09V value reported by Fuller et al [35] with an aircathode half-cell having a hydrogen Reference electrode
The results of two time-on-stream experiments at 160∘Care shown in Figure 4 Both curves show deactivationindicated by a decrease in potential difference with timeThe data show that deactivation continued for at least 20hours The two sets of data were obtained at different currentdensities and different H
2On-C
16H34
molar ratios Thedeactivation reported here with n-hexadecane is consistentwith deactivation reported earlier by Okrent and Heath [36]during direct hydrocarbon fuel cell experiments with decane
Two hypotheses can be suggested to explain deactivationCarbon monoxide a reaction intermediate formed duringthe overall reaction to produce the CO
2 shown in Figure 1
could poison the platinum catalyst at the anode Carbonmonoxide is a well-known poison on fuel cell platinumcatalysts [27] The other possibility is the formation ofcarbonaceous deposits Liebhafsky and Cairns [37] indicatedthe formation of dehydrogenated residues or carbonaceousmaterials during the operation of fuel cells with hydrocarbonfuels
The current densities in Figure 4 were integrated withrespect to time to obtain the cumulative amount of chargetransferred The potential difference in Figure 4 was plotted
Figure 4 Potential difference between the electrodes (V) andtime-on-stream (h) for an n-hexadecane fueled PAFC Anoden-hexadecane flow rate = 02mLh Cathode air flow rate =245mLmin Temperature= 160∘C Pressure = 1 atm Open trianglesare data obtained with current density 119895 = 004mAcm2 water flowrate = 51mLh and H
2On-C
16H34= 129 lowast SR Open squares are
data obtained with current density 119895 = 02mAcm2 water flowrate = 1mLh and H
2On-C
16H34= 25 lowast SR
0
01
02
03
04
05
06
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Pote
ntia
l diff
eren
ce (V
)
Cumulative charge transfer (Ccm2)
H2On-C16H34 = 129 lowast SR
H2On-C16H34 = 25 lowast SR
Figure 5 Potential difference between the electrodes (V) andcumulative charge transfer (Ccm2) for an n-hexadecane PAFCAnode n-hexadecane flow rate = 02mLh Cathode air flow rate =245mLmin Pressure = 1 atm Temperature = 160∘C Open trianglesare data obtained with water flow rate = 51mLh current density =004mAcm2 and H
2On-C
16H34
= 129 lowast SR Open squares aredata obtained with water flow rate = 1mLh current density =02mAcm2 and H
2On-C
16H34= 25 lowast SR
as a function of cumulative charge transferred in Figure 5The data indicate that at potential differences less than04V the slopes of the two lines are the same In otherwords deactivation is a linear function of charge transferredThat observation suggests that deactivation as representedby a decrease in potential difference is related to somephenomenon that correlates with the amount of chargetransferred regardless of the H
2On-C
16H34molar ratio
A hydrogenair polarization curve was measuredusing the PAFC after the first TOS experiment at 160∘C
Journal of Fuels 5
0010203040506070809
1
0 05 1 15 2 25 3 35 4 45
Reference
After 1st TOS experiment
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 6 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Open squaresare the Reference polarization curve Open triangles are the polar-ization curve obtained after the first time-on-stream experiment
(25 lowast SR H2On-C
16H34
= 81) In Figure 6 it is comparedto the ldquoReferencerdquo hydrogenair polarization curve fromFigure 3 The change between the Reference polarizationcurve and the one after the first time-on-stream experimentindicates that there had been a definite deterioration in thefuel cell performance The data in Figure 6 are consistentwith the deactivation observed during the TOS experimentsin Figure 4 If the two polarization curves are compared ata constant value of potential difference the current densityis much smaller after the TOS measurements than beforeEither the turnover frequency on a reaction site is muchsmaller or there are fewer reaction sites at which the reactionoccursThe only explanation is that something has preventedsmall hydrogen molecules from reacting to form electrons
Since deactivation during the TOS experiments wasobserved using both sets of operating conditions at 160∘Cfurther experiments were performed at a temperature of190∘C The MEA was treated by operating sequentially withhydrogen (6 h) water (6 h) and hydrogen (6 h) Then apolarization curve was measured The technique for mea-suring the polarization curve is indicated in Figure 7The current density was set to a constant value Thenthe potential difference was recorded until a steady-statevalue for the potential was obtained For one datum pointcorresponding to 04mAcm2 the steady-state value ofthe potential difference was extrapolated from the datain Figure 7 Generally at least one hour was requiredto obtain a steady-state value for the potential differenceFinally the steady-state values of the potential differencesobtained in Figure 7 were used in Figure 8 to constructa polarization curve for the n-hexadecanewater-air fuelcell
Some of the characteristics of the 190∘C n-hexadecaneairpolarization curve in Figure 8 are noteworthy The opencircuit potential of 05 V is much smaller than that of 093Vobtained for the hydrogenair fuel cell in Figure 3 It suggests
Figure 7 Potential difference between electrodes (V) as a functionof time (h) obtained with a PAFC Anode water flow rate =51mLh n-hexadecane flow rate = 02mLh Cathode air flowrate = 245mLmin Temperature = 190∘C pressure = 1 atm with anH2OC16H34ratio = 129 lowast SR The numbers on the top of each line
represent different current densities
0
01
02
03
04
05
06
0 005 01 015 02 025 03 035 04
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 8 Polarization curve for an n-hexadecane fueled PAFCpotential difference between the electrodes (V) and current density(mAcm2) Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
that the results in Figure 8 might represent the partialoxidation of carbon
C + 12
O2= CO 119864
0
298= 0711V (4)
as the rate limiting step in the overall reaction rather than theoxidation of n-hexadecane in (2) Equation (4) is composedof two half-cell reactions
C +H2O = CO + 2H+ + 2eminus anode (5)
2H+ + 2eminus + 12
O2= H2O cathode (6)
The difference between 0711 V and 05V might becaused by a combination of factors a temperature of 190∘Crather than 25∘C a cathode oxygen mole fraction of 021
6 Journal of Fuels
and an anode water vapour mole fraction representingequilibrium water vapour over phosphoric acid The opencircuit potential 05 V in Figure 8 is more consistent with thestandard electrochemical potential of the partial oxidationof carbon to carbon monoxide reaction 0711 V than withthe standard electrochemical potential of the oxidation ofcarbon monoxide to carbon dioxide (CO + (12)O
2=
CO2 1198640298= 133V) Initially two possible hypotheses were
suggested to explain deactivation either carbon monoxidepoisoning or deposition of carbonaceous material Equation(4) is consistent with the carbonaceous material hypothesisand not consistentwith carbonmonoxide hypothesis On thatbasis the hypothesis of deposition of carbonaceous materialseems to be the most likely explanation for the deactivationobserved during the time-on-stream experiments
Time-on-streammeasurements were also made at 190∘CThe TOS results at 190∘C are compared with those at 160∘Cin Figure 9 A steady-state operation was achieved for thelast six hours of the experiment at 190∘C A steady-stateoperation is a highly desirable result that is not alwaysachieved with a comparatively large hydrocarbon moleculesuch as hexadecane For example Okrent and Heath [36]reported unsteady cycling during which both the potentialand the current oscillated over time periods of approximately15 minutes when octane was the hydrocarbon fuel Althoughwe also observed cycling in some of our experiments thatphenomenon was not the object of our investigationThe factthat a steady-state has been demonstrated here for one set ofoperating conditions means that in principle fuel cells canoperate continuously using n-hexadecane (and presumablyother diesel type fuels)
Cleaning the MEA with water was mentioned in thediscussion pertaining to Figure 7 An example of water beingthe only reactant entering the fuel cell is shown in Figure 10The data in Figure 10 were obtained from an MEA that hadbeen used previously for 10 weeks in TOS experimentsWhenthe current density was maintained constant at a value of02mAcm2 the potential difference decreased continuouslyfor a period of 6 hours That indicated that a progressivelylarger overpotential was necessary (a larger driving force wasnecessary) tomaintain the current density at a constant valueWhen the current density was decreased to 01mAcm2 therewas an initial increase in the potential difference (smalleroverpotential) The potential difference gradually decreasedover the next 7 hours and then remained constant at 035Vfor the last 6 hours
The existence of a current densitywhenonlywaterwas fedto the fuel cell would require that some reaction must havebeen occurring Since no fuel (eg no n-hexadecane) wasfed to the fuel cell it is plausible that the reaction may haveoccurred between water and the carbonaceous material thathad been previously deposited on the MEA The existence ofa current density would also require proton migration acrossthe electrolyte The occurrence of the anode reaction shownin (5) would be consistent with both of these requirementsThe measurement of current density when only water wasfed to the fuel cell is consistent with the hypothesis thatcarbonaceous material was formed during deactivation andwas available for reaction during the water-only experiment
Figure 9 Potential differences between the electrodes (V) and time-on-stream (h) for an n-hexadecane PAFC Current density 119895 =004mAcm2 Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Pressure =1 atm
0
01
02
03
04
05
06
07
0 2 4 6 8 10 12 14 16 18 20Time-on-stream (h)
Pote
ntia
l diff
eren
ce (V
)
j = 02mAcm2j = 01mAcm2
Figure 10 Potential differences between the electrodes (V) as afunction of time-on-stream (h) when H
2O was the only feed stock
for the anode of a PAFC with a fouled MEA Anode water flowrate = 51mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
After the water-only experiments in Figure 10 werecompleted a hydrogen polarization curve was measured Itis compared with the Reference hydrogen polarization curvein Figure 11 A comparison of the results in Figure 11 (after thewater-only experiment) with the results in Figure 6 (after thefirst TOS experiment) indicates that a substantial improve-ment was caused by the water-only treatment That suggeststhe water-only experiment cleaned the MEA Cleaning of theMEA would be consistent with removal of a carbonaceousdeposit from the catalyst surface
The results reported here can be comparedwith other fuelcell systems Two of the important criteria are capital costand energy efficiency The capital cost is strongly influencedby the size of the fuel cell stack that in turn is a function ofcurrent density The theoretical energy efficiency is relatedto the thermodynamic efficiency of the reactions that occur
Journal of Fuels 7
0010203040506070809
1
0 05 1 15 2 25 3 35 4
After water-onlyexperiments
Reference
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 11 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Solid circles aredata obtained after a one-week experiment with water-only (on anMEA that had been used in TOS experiments for ten weeks) Opensquares are data for the Reference polarization curve
The reaction networks that occur vary with the particulartype of fuel cell systemThe operating cost of a fuel cell systemis strongly influenced by the energy efficiency
Small current densities were obtained for the low-temperature (190∘C) direct hydrocarbon (n-hexadecane)PAFC results without a reforming unit reported here Thereare extensive reviews describing results obtained by PAFCsoperating on hydrocarbons without a reforming unit [2ndash4]In general the current densities are quite small Thereforelarge reactors having a large capital cost would be requiredIn contrast Kim et al [38] reported much larger currentdensities using a higher temperature (700∘C) solid oxide fuelcell SOFC without a reforming unit when it was operatingon synthetic diesel fuel Interest in these systems specificallythe development of anodes continues to be an active area ofresearch [39 40] There have been several reviews of directhydrocarbon SOFCs without reforming units [13 41 42]Although no reforming unit was used they indicate thatinternal reforming occurs [13] Unfortunately the reformingreaction (internal or external) has a negative effect onenergy efficiency Approximately 25 of the hydrocarbonfuel must be used to provide the endothermic heat ofreaction for the reforming reaction At the low temperaturesused in this study the reforming reaction is thermodynam-ically unfavourable and does not occur Therefore the high-temperature SOFC systems will have a capital cost advantageover the lower temperature PAFC systemused here Howeverthe lower temperature PAFC system used here will havea theoretical energy efficiency advantage over the SOFCsystem
The use of an external reformer in combination with aPAFC system is a well-established technology that convertsthe hydrocarbon to hydrogen in a fuel processing system andthen uses the hydrogen as the fuel in a fuel cell system Bythe year 2006 more than 200 commercial plants had beensold [43] Nevertheless research on improving the reforming
process continues [44]The reforming reaction in an externalreformer has the same negative effect on energy efficiencythat was mentioned above for internal reforming The fuelprocessing system includes four processes steam reforminghigh-temperature water shift low-temperature shift andhydrogen purification Equipment for those four processeshas a substantial capital cost In contrast there is no capitalcost for a reformerfuel processor with the low-temperaturedirect hydrocarbon PAFC system described here
4 Conclusions
This study reported the first polarization curve evermeasuredforwhich n-hexadecanewas the fuel at the anode of a fuel cellThe current densities were found to be very small
Deactivation was observed in time-on-stream experi-ments Deactivation as measured by the change in potentialdifference was found to be a linear function of the cumulativecharge transferred across the electrolyte of the fuel cellDeactivation during fuel cell experiments with n-hexadecanewas confirmed by comparing hydrogen polarization curvesbefore and after the time-on-stream measurements For agiven potential difference the current densities were muchsmaller for the hydrogen polarization curves measured afterthe time-on-stream experiments
Experiments were performed in whichwater was the onlyreactant entering the fuel cell that had been used previouslyfor 10 weeks in time-on-stream experiments Current den-sities were measured during those experiments indicatingthat the water must have reacted with some type of speciesthat remained on the fuel cell catalyst at the end of thetime-on-stream experiments When a hydrogen polarizationcurvewasmeasured at the end of thewater-only experimentsit was close to that measured before the time-on-streamexperiments That indicates that the deactivating species onthe surface of the platinum particles had been removed andthat it was possible to regenerate deactivated MEAs
A hypothesis that carbonaceous material was depositedon the platinum anode catalyst particles was suggested toexplain the deactivation Four types of observations wereconsistent with that hypothesis (a) the change in potentialdifference during time-on-stream measurements (b) whenhydrogen polarization curves measured before and after thetime-on-stream experiments were compared the currentdensities measured after TOS were much smaller than thosemeasured before TOS (c) current densities were measuredwhen water was the only reactant entering the fuel cell Inorder to produce a current density water must have reactedwith some type of species that had been deposited on thesurface of the platinum particles and (d) the open circuitpotential of a n-hexadecane fuel cell 05 V was much closerto the standard electrochemical potential for the carbon-water reaction 0711 V than to that for the carbonmonoxide-water reaction 133 V Observation (d) makes a hypothesisof deactivation by carbonaceous materials more likely thandeactivation by carbon monoxide poisoning
Steady-state operation of the n-hexadecane fuel cellwithout additional deactivation was observed at one set of
8 Journal of Fuels
fuel cell operating conditionsThat observation demonstratesthat stable fuel cell operation is technically feasible whenn-hexadecane is the fuel at the anode of a fuel cell Itsuggests there ismerit in investigating fuel cell operationwithcommercial fuels such as petroleum diesel or biodiesel
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this research anddevelopment project was supported by a grant from Trans-port Canadarsquos Clean Rail Academic Grant Program and bya Discovery Grant from the Canadian Governmentrsquos NaturalSciences and Engineering Research Council
References
[1] J A A Ketelaar ldquoHistoryrdquo in Fuel Cell Systems L JM J Blomenand M N Mugerwa Eds p 20 Plenum Press New York NYUSA 1993
[2] E J Cairns ldquoAnodic oxidation of hydrocarbons and thehydrocarbon fuel cellrdquoAdvances in Electrochemistry Science andElectrochemical Engineering vol 8 pp 337ndash392 1971
[3] J O M Bockris and S Srinivasan ldquoElectrochemical combus-tion of organic substancesrdquo in Fuel CellsTheir Electrochemistrypp 357ndash411 McGraw-Hill New York NY USA 1969
[4] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 458ndash523 John Wiley amp Sons New York NY USA 1968
[5] S Bertholet Oxydation Electrocatalytique du Methane [PhDDissertation] Universite de Poitiers Poitiers France 1998
[6] C K Cheng J L Luo K T Chuang and A R SangerldquoPropane fuel cells using phosphoric-acid-doped polybenzim-idazole membranesrdquo The Journal of Physical Chemistry B vol109 no 26 pp 13036ndash13042 2005
[7] O Savadogo and F J Rodriguez Varela ldquoLow-temperaturedirect propane polymer electrolyte membranes fuel cellrdquo Jour-nal of New Materials for Electrochemical Systems vol 4 no 2pp 93ndash97 2001
[8] F J Rodrıguez Varela and O Savadogo ldquoReal-time massspectrometric analysis of the anode exhaust gases of a directpropane fuel cellrdquo Journal of the Electrochemical Society vol 152no 9 pp A1755ndashA1762 2005
[9] P Heo K Ito A Tomita and T Hibino ldquoA proton-conductingfuel cell operating with hydrocarbon fuelsrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7841ndash78442008
[10] B C H Steele I Kelly H Middleton and R Rudkin ldquoOxida-tion of methane in solid state electrochemical reactorsrdquo SolidState Ionics vol 28ndash30 no 2 pp 1547ndash1552 1988
[11] E P Murray T Tsai and S A Barnett ldquoA direct-methane fuelcell with a ceria-based anoderdquo Nature vol 400 no 6745 pp649ndash651 1999
[12] W Zhu C Xia J Fan R Peng and G Meng ldquoCeria coated Nias anodes for direct utilization of methane in low-temperature
solid oxide fuel cellsrdquo Journal of Power Sources vol 160 no 2pp 897ndash902 2006
[13] M D Gross J M Vohs and R J Gorte ldquoRecent progress inSOFC anodes for direct utilization of hydrocarbonsrdquo Journal ofMaterials Chemistry vol 17 no 30 pp 3071ndash3077 2007
[14] J G Lee C M Lee M Park and Y G Shul ldquoDirect methanefuel cell with La
2Sn2O7ndashNindashGd
01Ce09O195
anode and electro-spun La
06Sr04Co02Fe08O3minus120575
ndashGd01Ce09O195
cathoderdquo RoyalSociety of Chemistry Advances vol 3 no 29 pp 11816ndash118222013
[15] D Ding Z Liu L Li andC Xia ldquoAn octane-fueled low temper-ature solid oxide fuel cell with Ru-free anodesrdquo ElectrochemistryCommunications vol 10 no 9 pp 1295ndash1298 2008
[16] H Kishimoto K Yamaji T Horita et al ldquoFeasibility of liquidhydrocarbon fuels for SOFC with Ni-ScSZ anoderdquo Journal ofPower Sources vol 172 no 1 pp 67ndash71 2007
[17] Z F Zhou C Gallo M B Pague H Schobert and S N LvovldquoDirect oxidation of jet fuels and Pennsylvania crude oil in asolid oxide fuel cellrdquo Journal of Power Sources vol 133 no 2 pp181ndash187 2004
[18] G Psofogiannakis Y Bourgault B E Conway and M TernanldquoMathematical model for a direct propane phosphoric acid fuelcellrdquo Journal of Applied Electrochemistry vol 36 no 1 pp 115ndash130 2006
[19] H Khakdaman Y Bourgault and M Ternan ldquoComputationalmodeling of a direct propane fuel cellrdquo Journal of Power Sourcesvol 196 no 6 pp 3186ndash3194 2011
[20] H R Khakdaman Y Bourgault and M Ternan ldquoDirectpropane fuel cell anode with interdigitated flow fields two-dimensional modelrdquo Industrial amp Engineering ChemistryResearch vol 49 no 3 pp 1079ndash1085 2010
[21] G Psofogiannakis A St-Amant andM Ternan ldquoAb-initioDFTstudy of methane electro-oxidation mechanism on platinumrdquoJournal of Physical Chemistry B vol 110 pp 24593ndash24605 2006
[22] S Vafaeyan A St-Amant andM Ternan ldquoNickel alloy catalystsfor the anode of a high temperature PEM direct propane fuelcellrdquo Journal of Chemistry vol 2014 Article ID 151638 8 pages2014
[23] S Vafaeyan A St-Amant and M Ternan ldquoPropane fuel cellsselectivity for partial or complete reactionrdquo Journal of Fuels vol2014 Article ID 485045 9 pages 2014
[24] A Al-Othman A Y Tremblay W Pell et al ldquoA modified silicicacid (Si) and sulphuric acid (S)-ZrPPTFEglycerol compositemembrane for high temperature direct hydrocarbon fuel cellsrdquoJournal of Power Sources vol 224 pp 158ndash167 2013
[25] A Al-Othman A Y Tremblay W Pell Y Liu B A Peppleyand M Ternan ldquoThe effect of glycerol on the conductivity ofNafion-free ZrPPTFE composite membrane electrolytes fordirect hydrocarbon fuel cellsrdquo Journal of Power Sources vol 199pp 14ndash21 2012
[26] A Al-Othman A Y Tremblay W Pell et al ldquoZirconium phos-phate as the proton conducting material in direct hydrocarbonpolymer electrolyte membrane fuel cells operating above theboiling point of waterrdquo Journal of Power Sources vol 195 no9 pp 2520ndash2525 2010
[27] C G Farrell C L Gardner and M Ternan ldquoExperimental andmodelling studies of CO poisoning in PEM fuel cellsrdquo Journalof Power Sources vol 171 no 2 pp 282ndash293 2007
[28] R Fonocho C L Gardner and M Ternan ldquoA study of theelectrochemical hydrogenation of o-xylene in a PEM hydro-genation reactorrdquo Electrochimica Acta vol 75 pp 171ndash178 2012
Journal of Fuels 9
[29] N Sammes R Bove and K Stahl ldquoPhosphoric acid fuel cellsfundamentals and applicationsrdquo Current Opinion in Solid Stateand Materials Science vol 8 no 5 pp 372ndash378 2004
[30] J M King and H R Kunz ldquoPhosphoric acid electrolyte fuelcellsrdquo in Handbook of Fuel Cells W Vielstich A Lamm HA Gasteiger and H Yokokawa Eds vol 1 pp 287ndash300 JohnWiley amp Sons New York NY USA 2010
[31] S R Choudhury ldquoPhosphoric acid fuel cell technologyrdquo inRecent Trends in Fuel Cell Science and Technology S Basu Edpp 188ndash216 Springer New York NY USA 2007
[32] W Grubb and C J Michalske ldquoA high performance propanefuel cell operating in the temperature range of 150∘ndash200∘CrdquoJournal of The Electrochemical Society vol 111 no 9 p 10151964
[33] H A Liebhafsky andW T Grubb ldquoNormal alkanes at platinumanodesrdquo Fuel Preprints vol 11 no 2 p 134 1967
[34] V S Bagotzky Y B Vassiliev and O A Khazova ldquoGeneralizedscheme of chemisorption electrooxidation and electroreduc-tion of simple organic compounds on platinum group metalsrdquoJournal of Electroanalytical Chemistry and Interfacial Electro-chemistry vol 81 no 2 pp 229ndash238 1977
[35] T F Fuller F J Luczak and D J Wheeler ldquoElectrocatalystutilization in phosphoric acid fuel cellsrdquo Journal of the Electro-chemical Society vol 142 no 6 pp 1752ndash1757 1995
[36] E H Okrent and C E Heath ldquoA liquid hydrocarbon fuel cellbatteryrdquo in Fuel Cell Systems B Baker Ed Advances in Chem-istry pp 328ndash340 American Chemical Society WashingtonDC USA 1969
[37] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 485ndash510 John Wiley amp Sons New York NY USA 1968
[38] H Kim S Park J M Vohs and R J Gorte ldquoDirect oxidationof liquid fuels in a solid oxide fuel cellrdquo Journal of the Electro-chemical Society vol 148 no 7 pp A693ndashA695 2001
[39] S Islam and J M Hill ldquoBarium oxide promoted NiYSZ solid-oxide fuel cells for direct utilization of methanerdquo Journal ofMaterials Chemistry A vol 2 no 6 pp 1922ndash1929 2014
[40] C Yang J Li Y Lin J Liu F Chen and M Liu ldquoIn-situfabrication of CoFe allot nanoparticles structure (Pr
04Sr06)3
(Fe085
Nb015
)O7ceramic anode for direct hydrocarbon solid
oxde fuel cellsrdquo Nano Energy vol 11 pp 704ndash711 2015[41] S McIntosh and R J Gorte ldquoDirect hydrocarbon solid oxide
fuel cellsrdquo Chemical Reviews vol 104 no 10 pp 4845ndash48652004
[42] Y Zhao C Xia L Jia et al ldquoRecent progress on solid oxide fuelcell lowering temperature and utilizing non-hydrogen fuelsrdquoInternational Journal of Hydrogen Energy vol 38 no 36 pp16498ndash16517 2013
[43] S Srinivasan Fuel Cells From Fundamentals to ApplicationsSpringer New York NY USA 2006
[44] M RWalluk J LinMGWaller D F Smith andTA TraboldldquoDiesel auto-thermal reforming for solid oxide fuel cell systemsanode off-gas recycle simulationrdquo Applied Energy vol 130 pp94ndash102 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
2 Journal of Fuels
Direct hydrocarbon fuel cells have other advantagesDHFC systems have lower capital costs than other fuelcell systems because the fuel processing systems (steamreforming etc) for hydrogen and methanol fuels are notrequired In addition the infrastructure already exists fordiesel fuel and other petroleum derived fuels That is not thecase for hydrogen or methanol fuels Storage of liquid fuelssuch as diesel fuel ismuch easier than storage of gaseous fuelssuch as hydrogen
Unfortunately DHFCs have one major disadvantageTheir current densities are much smaller than those ofhydrogen and methanol fuel cells Work in our laboratory isbeing performed to understand the characteristics of DHFCswith a long-term objective of improving their performance
William Grove demonstrated the first fuel cell operationin 1839 using hydrogen as the fuel He was also creditedwith suggesting possible commercial opportunities if coalwood or other combustibles could replace hydrogen [1]which would be DHFCs Direct hydrocarbon fuel cells wereinvestigated intensely in the 1960s Three reviews of theDHFC work up to that time are available [2ndash4]
Research on DHFCs has continued Low-temperaturefuel cell studies (lt100∘C) were performed on methane byBertholet [5] and on propane by Cheng et al [6] andby Savadogo and Rodriguez Varela [7 8] Heo et al [9]performed intermediate temperature fuel cell studies (100ndash300∘C) using propane A larger number of DHFC studieshave been performed on solid oxide fuel cells Studies usinglow molecular weight hydrocarbons frommethane to butanewere performed by Steele et al [10] Murray et al [11] Zhu etal [12] Gross et al [13] and Lee et al [14] Larger moleculeswere studied by Ding et al [15] (octane) Kishimoto et al [16](n-dodecane) and Zhou et al [17] (jet fuel) Our own workhas focused on modeling the fuel cell reactor [18ndash20] mod-eling the fuel cell catalyst [21ndash23] experimental developmentof an electrolyte that is appropriate for temperatures abovethe boiling point of water [24ndash26] and experimental fuel cellstudies [27 28]
Phosphoric acid fuel cell systems have an extensivedevelopment history A 250ndash400 kW fuel cell system toproduce stationary electric power was developed by Prattand WhitneyONSIUTC Power 300 units were built in19 different countries The company was sold to ClearEdgePower and was recently acquired by Doosan Industries Thephosphoric acid fuel cell technology has been documentedextensively [29ndash32]
The fuel in this work was n-hexadecane There were onlythree data points reported previously in a fuel cell study thatexamined a variety of fuels [33] This is the first fuel cellstudy devoted exclusively to n-hexadecane In a direct n-hexadecane phosphoric acid fuel cell the overall reaction is
C16H34(g) + 492
O2(g) 997888rarr 16CO
2(g) + 17H
2O (g) (1)
The anode half-cell reaction is
C16H34(g) + 32H
2O (g) 997888rarr 16CO
2(g) + 98H+ + 98eminus
(2)
The cathode half-cell reaction is49
2
O2(g) + 98H+ + 98eminus 997888rarr 49H
2O (g) (3)
where the (g) represents the gas phase The anode stoi-chiometric ratio SR = H
2OC16H34
is 32 One mole of n-hexadecane reacts with 32 moles of water at the anode andgenerates 98 moles of protons and electrons The protonsmigrate through the electrolyte to the cathode where theoxygen reduction reaction occurs
Bagotzky et al [34] described a reaction mechanism fordirect hydrocarbon fuel cells using methane as a feedstockThe Bagotskymechanismwasmodified as shown in Figure 1to describe n-hexadecane The desired product is CO
2
However alcohols aldehydes carboxylic acids and lowermolecular weight hydrocarbons are possible by-productsThree reactions are shown in Figure 1 dehydrogenation (fromboth carbon and oxygen atoms) hydroxylation and CndashCbond cleavage Two reactions are not shown water dissoci-ation (H
2O rarr H + OH) and hydrogen atom ionization
(H rarr H+ + eminus) Hydrogen ionization is an electrochemicalreaction and therefore is influenced by potential The otherfour reactions are chemical reactions and are not influencedby potential
The objective of the work described here was to identify aset of operating conditions that would permit stable contin-uous operation of a direct hydrocarbon phosphoric acid fuelcell using n-hexadecane as the fuel
2 Experimental
A schematic diagram of the direct n-hexadecane fueledphosphoric acid fuel cell (PAFC) system is shown in Figure 2The overall system consists of an air cylinder a hydrogencylinder one Galvanostat two syringe pumps a vaporizera phosphoric acid fuel cell (PAFC = Electrochem FC-25-02MA) and a fuel cell test station Both gaseous and liquidfuels can be used in this fuel cell system Deionized waterand n-hexadecane were introduced into the vaporizer by thesyringe pumps The liquid fuels were expected to vaporizebefore reaching the anode of the fuel cell Air was fed to thecathode at a constant flow rate On those occasions whenhydrogen was used as the fuel the pumps were stopped andthe valve in Figure 2 was opened
The membrane electrode assembly (MEA) used in ourfuel cell work had five layers two gas diffusion layers (GDL)two catalyst layers (CL) and a liquid electrolyte layerThe gasdiffusion layers were Teflon coated Toray paper
The liquid electrolyte was initially 85 (146M) phos-phoric acid which was held in a SiC matrix between theanode and cathode catalyst layers Platinum (05mg Ptcm2)supported on carbon (10 Pt on C) was the catalyst in bothanode and cathode catalyst layers The fuel cells had a facearea of 25 cm2 A pin-type flow field was machined in agraphite plate The current collectors were sheets of coppermetal that had been gold plated on both sides Silicone rubberflexible heaters were attached to each current collector
Several types of experiments were performed Hydrogenpolarization curves were measured to determine the state
Figure 1 Diagram of a modified Bagotsky anode reaction mechanism H(CH2)119873CH3= hexadecane if119873 = 15 +OH = Hydroxylation minusH =
Dehydrogenation and bc = CndashC bond cleavage Two reactions are not shown water dissociation H2O = H + OH and the electrochemical
reaction H = H+ + eminus
Flowmeter
Air H2
n-Hexadecane
Deionized H2O
Syringe pumps
AD converter
Vaporizer
Galvanostat
Ano
de
Elec
troly
te
Cath
ode
Fume hood
Condensate
Computer
Figure 2 Diagram of a direct n-hexadecane fueled phosphoric acid fuel cell system
of the MEA in the fuel cell A polarization curve showsthe potential difference as a function of current density n-Hexadecane polarization curves were measured Two typesof time-on-stream experiments were performed (H
2O with
n-C16H34
and H2O only) The time-on-stream experiments
were performed at (a) different molar ratios of water to n-hexadecane (b) different current densities and (c) differenttemperatures
The following operating conditions were used Sepa-rate syringe pumps were used to feed both water and n-hexadecane The water flow rate was expressed as a functionof the stoichiometric ratio (SR) of H
2OC16H34
in (2) for
the anode half reaction A constant flow rate of n-hexadecane(02mLh) was used in all experiments The two water flowrates and their stoichiometric ratios were 1mLh (25 lowast SRH2OC16H34
= 80) and 51mLh (129 lowast SR H2OC16H34
=414) Some experiments were performed with only waterbeing fed to the fuel cell The experiments were performedat two temperatures 160∘C and 190∘C
A Hokuto Denko HA-301 Galvanostat was used to adjustthe potential difference between the anode and cathode of thephosphoric acid fuel cell to maintain the chosen current at aconstant value The potential difference was recorded everysecond using a Lab View data logger
4 Journal of Fuels
0010203040506070809
1
0 05 1 15 2 25 3 35 4 45
Pote
ntia
l diff
eren
ce (V
)
New MEA
Reference
Current density (mAcm2)
Figure 3 Polarization curve for a hydrogen fueled PAFC poten-tial difference between the electrodes (Volts) and current density(mAcm2) Open diamonds are data obtained on a newMEA Opensquares are data obtained on an MEA that had been conditionedin previous experiments with low molecular weight hydrocarbons(ethylene propane) Anode hydrogen flow rate = 96mLh Cath-ode air flow rate = 245mLmin Temperature = 160∘C Pressure =1 atm
3 Results and Discussion
Two hydrogenair polarization curves obtained with a PAFCare shown in Figure 3 The upper curve was the firstexperiment performed with a new MEA The lower curvewas measured after some conditioning experiments hadbeen performed with low molecular weight hydrocarbons(ethylene propane) It is an indication of the condition ofthe MEA at the beginning of this investigation and will bereferred to as the Reference polarization curve The opencircuit potential in Figure 3 is about 093V It is comparableto the 09V value reported by Fuller et al [35] with an aircathode half-cell having a hydrogen Reference electrode
The results of two time-on-stream experiments at 160∘Care shown in Figure 4 Both curves show deactivationindicated by a decrease in potential difference with timeThe data show that deactivation continued for at least 20hours The two sets of data were obtained at different currentdensities and different H
2On-C
16H34
molar ratios Thedeactivation reported here with n-hexadecane is consistentwith deactivation reported earlier by Okrent and Heath [36]during direct hydrocarbon fuel cell experiments with decane
Two hypotheses can be suggested to explain deactivationCarbon monoxide a reaction intermediate formed duringthe overall reaction to produce the CO
2 shown in Figure 1
could poison the platinum catalyst at the anode Carbonmonoxide is a well-known poison on fuel cell platinumcatalysts [27] The other possibility is the formation ofcarbonaceous deposits Liebhafsky and Cairns [37] indicatedthe formation of dehydrogenated residues or carbonaceousmaterials during the operation of fuel cells with hydrocarbonfuels
The current densities in Figure 4 were integrated withrespect to time to obtain the cumulative amount of chargetransferred The potential difference in Figure 4 was plotted
Figure 4 Potential difference between the electrodes (V) andtime-on-stream (h) for an n-hexadecane fueled PAFC Anoden-hexadecane flow rate = 02mLh Cathode air flow rate =245mLmin Temperature= 160∘C Pressure = 1 atm Open trianglesare data obtained with current density 119895 = 004mAcm2 water flowrate = 51mLh and H
2On-C
16H34= 129 lowast SR Open squares are
data obtained with current density 119895 = 02mAcm2 water flowrate = 1mLh and H
2On-C
16H34= 25 lowast SR
0
01
02
03
04
05
06
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Pote
ntia
l diff
eren
ce (V
)
Cumulative charge transfer (Ccm2)
H2On-C16H34 = 129 lowast SR
H2On-C16H34 = 25 lowast SR
Figure 5 Potential difference between the electrodes (V) andcumulative charge transfer (Ccm2) for an n-hexadecane PAFCAnode n-hexadecane flow rate = 02mLh Cathode air flow rate =245mLmin Pressure = 1 atm Temperature = 160∘C Open trianglesare data obtained with water flow rate = 51mLh current density =004mAcm2 and H
2On-C
16H34
= 129 lowast SR Open squares aredata obtained with water flow rate = 1mLh current density =02mAcm2 and H
2On-C
16H34= 25 lowast SR
as a function of cumulative charge transferred in Figure 5The data indicate that at potential differences less than04V the slopes of the two lines are the same In otherwords deactivation is a linear function of charge transferredThat observation suggests that deactivation as representedby a decrease in potential difference is related to somephenomenon that correlates with the amount of chargetransferred regardless of the H
2On-C
16H34molar ratio
A hydrogenair polarization curve was measuredusing the PAFC after the first TOS experiment at 160∘C
Journal of Fuels 5
0010203040506070809
1
0 05 1 15 2 25 3 35 4 45
Reference
After 1st TOS experiment
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 6 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Open squaresare the Reference polarization curve Open triangles are the polar-ization curve obtained after the first time-on-stream experiment
(25 lowast SR H2On-C
16H34
= 81) In Figure 6 it is comparedto the ldquoReferencerdquo hydrogenair polarization curve fromFigure 3 The change between the Reference polarizationcurve and the one after the first time-on-stream experimentindicates that there had been a definite deterioration in thefuel cell performance The data in Figure 6 are consistentwith the deactivation observed during the TOS experimentsin Figure 4 If the two polarization curves are compared ata constant value of potential difference the current densityis much smaller after the TOS measurements than beforeEither the turnover frequency on a reaction site is muchsmaller or there are fewer reaction sites at which the reactionoccursThe only explanation is that something has preventedsmall hydrogen molecules from reacting to form electrons
Since deactivation during the TOS experiments wasobserved using both sets of operating conditions at 160∘Cfurther experiments were performed at a temperature of190∘C The MEA was treated by operating sequentially withhydrogen (6 h) water (6 h) and hydrogen (6 h) Then apolarization curve was measured The technique for mea-suring the polarization curve is indicated in Figure 7The current density was set to a constant value Thenthe potential difference was recorded until a steady-statevalue for the potential was obtained For one datum pointcorresponding to 04mAcm2 the steady-state value ofthe potential difference was extrapolated from the datain Figure 7 Generally at least one hour was requiredto obtain a steady-state value for the potential differenceFinally the steady-state values of the potential differencesobtained in Figure 7 were used in Figure 8 to constructa polarization curve for the n-hexadecanewater-air fuelcell
Some of the characteristics of the 190∘C n-hexadecaneairpolarization curve in Figure 8 are noteworthy The opencircuit potential of 05 V is much smaller than that of 093Vobtained for the hydrogenair fuel cell in Figure 3 It suggests
Figure 7 Potential difference between electrodes (V) as a functionof time (h) obtained with a PAFC Anode water flow rate =51mLh n-hexadecane flow rate = 02mLh Cathode air flowrate = 245mLmin Temperature = 190∘C pressure = 1 atm with anH2OC16H34ratio = 129 lowast SR The numbers on the top of each line
represent different current densities
0
01
02
03
04
05
06
0 005 01 015 02 025 03 035 04
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 8 Polarization curve for an n-hexadecane fueled PAFCpotential difference between the electrodes (V) and current density(mAcm2) Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
that the results in Figure 8 might represent the partialoxidation of carbon
C + 12
O2= CO 119864
0
298= 0711V (4)
as the rate limiting step in the overall reaction rather than theoxidation of n-hexadecane in (2) Equation (4) is composedof two half-cell reactions
C +H2O = CO + 2H+ + 2eminus anode (5)
2H+ + 2eminus + 12
O2= H2O cathode (6)
The difference between 0711 V and 05V might becaused by a combination of factors a temperature of 190∘Crather than 25∘C a cathode oxygen mole fraction of 021
6 Journal of Fuels
and an anode water vapour mole fraction representingequilibrium water vapour over phosphoric acid The opencircuit potential 05 V in Figure 8 is more consistent with thestandard electrochemical potential of the partial oxidationof carbon to carbon monoxide reaction 0711 V than withthe standard electrochemical potential of the oxidation ofcarbon monoxide to carbon dioxide (CO + (12)O
2=
CO2 1198640298= 133V) Initially two possible hypotheses were
suggested to explain deactivation either carbon monoxidepoisoning or deposition of carbonaceous material Equation(4) is consistent with the carbonaceous material hypothesisand not consistentwith carbonmonoxide hypothesis On thatbasis the hypothesis of deposition of carbonaceous materialseems to be the most likely explanation for the deactivationobserved during the time-on-stream experiments
Time-on-streammeasurements were also made at 190∘CThe TOS results at 190∘C are compared with those at 160∘Cin Figure 9 A steady-state operation was achieved for thelast six hours of the experiment at 190∘C A steady-stateoperation is a highly desirable result that is not alwaysachieved with a comparatively large hydrocarbon moleculesuch as hexadecane For example Okrent and Heath [36]reported unsteady cycling during which both the potentialand the current oscillated over time periods of approximately15 minutes when octane was the hydrocarbon fuel Althoughwe also observed cycling in some of our experiments thatphenomenon was not the object of our investigationThe factthat a steady-state has been demonstrated here for one set ofoperating conditions means that in principle fuel cells canoperate continuously using n-hexadecane (and presumablyother diesel type fuels)
Cleaning the MEA with water was mentioned in thediscussion pertaining to Figure 7 An example of water beingthe only reactant entering the fuel cell is shown in Figure 10The data in Figure 10 were obtained from an MEA that hadbeen used previously for 10 weeks in TOS experimentsWhenthe current density was maintained constant at a value of02mAcm2 the potential difference decreased continuouslyfor a period of 6 hours That indicated that a progressivelylarger overpotential was necessary (a larger driving force wasnecessary) tomaintain the current density at a constant valueWhen the current density was decreased to 01mAcm2 therewas an initial increase in the potential difference (smalleroverpotential) The potential difference gradually decreasedover the next 7 hours and then remained constant at 035Vfor the last 6 hours
The existence of a current densitywhenonlywaterwas fedto the fuel cell would require that some reaction must havebeen occurring Since no fuel (eg no n-hexadecane) wasfed to the fuel cell it is plausible that the reaction may haveoccurred between water and the carbonaceous material thathad been previously deposited on the MEA The existence ofa current density would also require proton migration acrossthe electrolyte The occurrence of the anode reaction shownin (5) would be consistent with both of these requirementsThe measurement of current density when only water wasfed to the fuel cell is consistent with the hypothesis thatcarbonaceous material was formed during deactivation andwas available for reaction during the water-only experiment
Figure 9 Potential differences between the electrodes (V) and time-on-stream (h) for an n-hexadecane PAFC Current density 119895 =004mAcm2 Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Pressure =1 atm
0
01
02
03
04
05
06
07
0 2 4 6 8 10 12 14 16 18 20Time-on-stream (h)
Pote
ntia
l diff
eren
ce (V
)
j = 02mAcm2j = 01mAcm2
Figure 10 Potential differences between the electrodes (V) as afunction of time-on-stream (h) when H
2O was the only feed stock
for the anode of a PAFC with a fouled MEA Anode water flowrate = 51mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
After the water-only experiments in Figure 10 werecompleted a hydrogen polarization curve was measured Itis compared with the Reference hydrogen polarization curvein Figure 11 A comparison of the results in Figure 11 (after thewater-only experiment) with the results in Figure 6 (after thefirst TOS experiment) indicates that a substantial improve-ment was caused by the water-only treatment That suggeststhe water-only experiment cleaned the MEA Cleaning of theMEA would be consistent with removal of a carbonaceousdeposit from the catalyst surface
The results reported here can be comparedwith other fuelcell systems Two of the important criteria are capital costand energy efficiency The capital cost is strongly influencedby the size of the fuel cell stack that in turn is a function ofcurrent density The theoretical energy efficiency is relatedto the thermodynamic efficiency of the reactions that occur
Journal of Fuels 7
0010203040506070809
1
0 05 1 15 2 25 3 35 4
After water-onlyexperiments
Reference
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 11 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Solid circles aredata obtained after a one-week experiment with water-only (on anMEA that had been used in TOS experiments for ten weeks) Opensquares are data for the Reference polarization curve
The reaction networks that occur vary with the particulartype of fuel cell systemThe operating cost of a fuel cell systemis strongly influenced by the energy efficiency
Small current densities were obtained for the low-temperature (190∘C) direct hydrocarbon (n-hexadecane)PAFC results without a reforming unit reported here Thereare extensive reviews describing results obtained by PAFCsoperating on hydrocarbons without a reforming unit [2ndash4]In general the current densities are quite small Thereforelarge reactors having a large capital cost would be requiredIn contrast Kim et al [38] reported much larger currentdensities using a higher temperature (700∘C) solid oxide fuelcell SOFC without a reforming unit when it was operatingon synthetic diesel fuel Interest in these systems specificallythe development of anodes continues to be an active area ofresearch [39 40] There have been several reviews of directhydrocarbon SOFCs without reforming units [13 41 42]Although no reforming unit was used they indicate thatinternal reforming occurs [13] Unfortunately the reformingreaction (internal or external) has a negative effect onenergy efficiency Approximately 25 of the hydrocarbonfuel must be used to provide the endothermic heat ofreaction for the reforming reaction At the low temperaturesused in this study the reforming reaction is thermodynam-ically unfavourable and does not occur Therefore the high-temperature SOFC systems will have a capital cost advantageover the lower temperature PAFC systemused here Howeverthe lower temperature PAFC system used here will havea theoretical energy efficiency advantage over the SOFCsystem
The use of an external reformer in combination with aPAFC system is a well-established technology that convertsthe hydrocarbon to hydrogen in a fuel processing system andthen uses the hydrogen as the fuel in a fuel cell system Bythe year 2006 more than 200 commercial plants had beensold [43] Nevertheless research on improving the reforming
process continues [44]The reforming reaction in an externalreformer has the same negative effect on energy efficiencythat was mentioned above for internal reforming The fuelprocessing system includes four processes steam reforminghigh-temperature water shift low-temperature shift andhydrogen purification Equipment for those four processeshas a substantial capital cost In contrast there is no capitalcost for a reformerfuel processor with the low-temperaturedirect hydrocarbon PAFC system described here
4 Conclusions
This study reported the first polarization curve evermeasuredforwhich n-hexadecanewas the fuel at the anode of a fuel cellThe current densities were found to be very small
Deactivation was observed in time-on-stream experi-ments Deactivation as measured by the change in potentialdifference was found to be a linear function of the cumulativecharge transferred across the electrolyte of the fuel cellDeactivation during fuel cell experiments with n-hexadecanewas confirmed by comparing hydrogen polarization curvesbefore and after the time-on-stream measurements For agiven potential difference the current densities were muchsmaller for the hydrogen polarization curves measured afterthe time-on-stream experiments
Experiments were performed in whichwater was the onlyreactant entering the fuel cell that had been used previouslyfor 10 weeks in time-on-stream experiments Current den-sities were measured during those experiments indicatingthat the water must have reacted with some type of speciesthat remained on the fuel cell catalyst at the end of thetime-on-stream experiments When a hydrogen polarizationcurvewasmeasured at the end of thewater-only experimentsit was close to that measured before the time-on-streamexperiments That indicates that the deactivating species onthe surface of the platinum particles had been removed andthat it was possible to regenerate deactivated MEAs
A hypothesis that carbonaceous material was depositedon the platinum anode catalyst particles was suggested toexplain the deactivation Four types of observations wereconsistent with that hypothesis (a) the change in potentialdifference during time-on-stream measurements (b) whenhydrogen polarization curves measured before and after thetime-on-stream experiments were compared the currentdensities measured after TOS were much smaller than thosemeasured before TOS (c) current densities were measuredwhen water was the only reactant entering the fuel cell Inorder to produce a current density water must have reactedwith some type of species that had been deposited on thesurface of the platinum particles and (d) the open circuitpotential of a n-hexadecane fuel cell 05 V was much closerto the standard electrochemical potential for the carbon-water reaction 0711 V than to that for the carbonmonoxide-water reaction 133 V Observation (d) makes a hypothesisof deactivation by carbonaceous materials more likely thandeactivation by carbon monoxide poisoning
Steady-state operation of the n-hexadecane fuel cellwithout additional deactivation was observed at one set of
8 Journal of Fuels
fuel cell operating conditionsThat observation demonstratesthat stable fuel cell operation is technically feasible whenn-hexadecane is the fuel at the anode of a fuel cell Itsuggests there ismerit in investigating fuel cell operationwithcommercial fuels such as petroleum diesel or biodiesel
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this research anddevelopment project was supported by a grant from Trans-port Canadarsquos Clean Rail Academic Grant Program and bya Discovery Grant from the Canadian Governmentrsquos NaturalSciences and Engineering Research Council
References
[1] J A A Ketelaar ldquoHistoryrdquo in Fuel Cell Systems L JM J Blomenand M N Mugerwa Eds p 20 Plenum Press New York NYUSA 1993
[2] E J Cairns ldquoAnodic oxidation of hydrocarbons and thehydrocarbon fuel cellrdquoAdvances in Electrochemistry Science andElectrochemical Engineering vol 8 pp 337ndash392 1971
[3] J O M Bockris and S Srinivasan ldquoElectrochemical combus-tion of organic substancesrdquo in Fuel CellsTheir Electrochemistrypp 357ndash411 McGraw-Hill New York NY USA 1969
[4] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 458ndash523 John Wiley amp Sons New York NY USA 1968
[5] S Bertholet Oxydation Electrocatalytique du Methane [PhDDissertation] Universite de Poitiers Poitiers France 1998
[6] C K Cheng J L Luo K T Chuang and A R SangerldquoPropane fuel cells using phosphoric-acid-doped polybenzim-idazole membranesrdquo The Journal of Physical Chemistry B vol109 no 26 pp 13036ndash13042 2005
[7] O Savadogo and F J Rodriguez Varela ldquoLow-temperaturedirect propane polymer electrolyte membranes fuel cellrdquo Jour-nal of New Materials for Electrochemical Systems vol 4 no 2pp 93ndash97 2001
[8] F J Rodrıguez Varela and O Savadogo ldquoReal-time massspectrometric analysis of the anode exhaust gases of a directpropane fuel cellrdquo Journal of the Electrochemical Society vol 152no 9 pp A1755ndashA1762 2005
[9] P Heo K Ito A Tomita and T Hibino ldquoA proton-conductingfuel cell operating with hydrocarbon fuelsrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7841ndash78442008
[10] B C H Steele I Kelly H Middleton and R Rudkin ldquoOxida-tion of methane in solid state electrochemical reactorsrdquo SolidState Ionics vol 28ndash30 no 2 pp 1547ndash1552 1988
[11] E P Murray T Tsai and S A Barnett ldquoA direct-methane fuelcell with a ceria-based anoderdquo Nature vol 400 no 6745 pp649ndash651 1999
[12] W Zhu C Xia J Fan R Peng and G Meng ldquoCeria coated Nias anodes for direct utilization of methane in low-temperature
solid oxide fuel cellsrdquo Journal of Power Sources vol 160 no 2pp 897ndash902 2006
[13] M D Gross J M Vohs and R J Gorte ldquoRecent progress inSOFC anodes for direct utilization of hydrocarbonsrdquo Journal ofMaterials Chemistry vol 17 no 30 pp 3071ndash3077 2007
[14] J G Lee C M Lee M Park and Y G Shul ldquoDirect methanefuel cell with La
2Sn2O7ndashNindashGd
01Ce09O195
anode and electro-spun La
06Sr04Co02Fe08O3minus120575
ndashGd01Ce09O195
cathoderdquo RoyalSociety of Chemistry Advances vol 3 no 29 pp 11816ndash118222013
[15] D Ding Z Liu L Li andC Xia ldquoAn octane-fueled low temper-ature solid oxide fuel cell with Ru-free anodesrdquo ElectrochemistryCommunications vol 10 no 9 pp 1295ndash1298 2008
[16] H Kishimoto K Yamaji T Horita et al ldquoFeasibility of liquidhydrocarbon fuels for SOFC with Ni-ScSZ anoderdquo Journal ofPower Sources vol 172 no 1 pp 67ndash71 2007
[17] Z F Zhou C Gallo M B Pague H Schobert and S N LvovldquoDirect oxidation of jet fuels and Pennsylvania crude oil in asolid oxide fuel cellrdquo Journal of Power Sources vol 133 no 2 pp181ndash187 2004
[18] G Psofogiannakis Y Bourgault B E Conway and M TernanldquoMathematical model for a direct propane phosphoric acid fuelcellrdquo Journal of Applied Electrochemistry vol 36 no 1 pp 115ndash130 2006
[19] H Khakdaman Y Bourgault and M Ternan ldquoComputationalmodeling of a direct propane fuel cellrdquo Journal of Power Sourcesvol 196 no 6 pp 3186ndash3194 2011
[20] H R Khakdaman Y Bourgault and M Ternan ldquoDirectpropane fuel cell anode with interdigitated flow fields two-dimensional modelrdquo Industrial amp Engineering ChemistryResearch vol 49 no 3 pp 1079ndash1085 2010
[21] G Psofogiannakis A St-Amant andM Ternan ldquoAb-initioDFTstudy of methane electro-oxidation mechanism on platinumrdquoJournal of Physical Chemistry B vol 110 pp 24593ndash24605 2006
[22] S Vafaeyan A St-Amant andM Ternan ldquoNickel alloy catalystsfor the anode of a high temperature PEM direct propane fuelcellrdquo Journal of Chemistry vol 2014 Article ID 151638 8 pages2014
[23] S Vafaeyan A St-Amant and M Ternan ldquoPropane fuel cellsselectivity for partial or complete reactionrdquo Journal of Fuels vol2014 Article ID 485045 9 pages 2014
[24] A Al-Othman A Y Tremblay W Pell et al ldquoA modified silicicacid (Si) and sulphuric acid (S)-ZrPPTFEglycerol compositemembrane for high temperature direct hydrocarbon fuel cellsrdquoJournal of Power Sources vol 224 pp 158ndash167 2013
[25] A Al-Othman A Y Tremblay W Pell Y Liu B A Peppleyand M Ternan ldquoThe effect of glycerol on the conductivity ofNafion-free ZrPPTFE composite membrane electrolytes fordirect hydrocarbon fuel cellsrdquo Journal of Power Sources vol 199pp 14ndash21 2012
[26] A Al-Othman A Y Tremblay W Pell et al ldquoZirconium phos-phate as the proton conducting material in direct hydrocarbonpolymer electrolyte membrane fuel cells operating above theboiling point of waterrdquo Journal of Power Sources vol 195 no9 pp 2520ndash2525 2010
[27] C G Farrell C L Gardner and M Ternan ldquoExperimental andmodelling studies of CO poisoning in PEM fuel cellsrdquo Journalof Power Sources vol 171 no 2 pp 282ndash293 2007
[28] R Fonocho C L Gardner and M Ternan ldquoA study of theelectrochemical hydrogenation of o-xylene in a PEM hydro-genation reactorrdquo Electrochimica Acta vol 75 pp 171ndash178 2012
Journal of Fuels 9
[29] N Sammes R Bove and K Stahl ldquoPhosphoric acid fuel cellsfundamentals and applicationsrdquo Current Opinion in Solid Stateand Materials Science vol 8 no 5 pp 372ndash378 2004
[30] J M King and H R Kunz ldquoPhosphoric acid electrolyte fuelcellsrdquo in Handbook of Fuel Cells W Vielstich A Lamm HA Gasteiger and H Yokokawa Eds vol 1 pp 287ndash300 JohnWiley amp Sons New York NY USA 2010
[31] S R Choudhury ldquoPhosphoric acid fuel cell technologyrdquo inRecent Trends in Fuel Cell Science and Technology S Basu Edpp 188ndash216 Springer New York NY USA 2007
[32] W Grubb and C J Michalske ldquoA high performance propanefuel cell operating in the temperature range of 150∘ndash200∘CrdquoJournal of The Electrochemical Society vol 111 no 9 p 10151964
[33] H A Liebhafsky andW T Grubb ldquoNormal alkanes at platinumanodesrdquo Fuel Preprints vol 11 no 2 p 134 1967
[34] V S Bagotzky Y B Vassiliev and O A Khazova ldquoGeneralizedscheme of chemisorption electrooxidation and electroreduc-tion of simple organic compounds on platinum group metalsrdquoJournal of Electroanalytical Chemistry and Interfacial Electro-chemistry vol 81 no 2 pp 229ndash238 1977
[35] T F Fuller F J Luczak and D J Wheeler ldquoElectrocatalystutilization in phosphoric acid fuel cellsrdquo Journal of the Electro-chemical Society vol 142 no 6 pp 1752ndash1757 1995
[36] E H Okrent and C E Heath ldquoA liquid hydrocarbon fuel cellbatteryrdquo in Fuel Cell Systems B Baker Ed Advances in Chem-istry pp 328ndash340 American Chemical Society WashingtonDC USA 1969
[37] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 485ndash510 John Wiley amp Sons New York NY USA 1968
[38] H Kim S Park J M Vohs and R J Gorte ldquoDirect oxidationof liquid fuels in a solid oxide fuel cellrdquo Journal of the Electro-chemical Society vol 148 no 7 pp A693ndashA695 2001
[39] S Islam and J M Hill ldquoBarium oxide promoted NiYSZ solid-oxide fuel cells for direct utilization of methanerdquo Journal ofMaterials Chemistry A vol 2 no 6 pp 1922ndash1929 2014
[40] C Yang J Li Y Lin J Liu F Chen and M Liu ldquoIn-situfabrication of CoFe allot nanoparticles structure (Pr
04Sr06)3
(Fe085
Nb015
)O7ceramic anode for direct hydrocarbon solid
oxde fuel cellsrdquo Nano Energy vol 11 pp 704ndash711 2015[41] S McIntosh and R J Gorte ldquoDirect hydrocarbon solid oxide
fuel cellsrdquo Chemical Reviews vol 104 no 10 pp 4845ndash48652004
[42] Y Zhao C Xia L Jia et al ldquoRecent progress on solid oxide fuelcell lowering temperature and utilizing non-hydrogen fuelsrdquoInternational Journal of Hydrogen Energy vol 38 no 36 pp16498ndash16517 2013
[43] S Srinivasan Fuel Cells From Fundamentals to ApplicationsSpringer New York NY USA 2006
[44] M RWalluk J LinMGWaller D F Smith andTA TraboldldquoDiesel auto-thermal reforming for solid oxide fuel cell systemsanode off-gas recycle simulationrdquo Applied Energy vol 130 pp94ndash102 2014
Figure 1 Diagram of a modified Bagotsky anode reaction mechanism H(CH2)119873CH3= hexadecane if119873 = 15 +OH = Hydroxylation minusH =
Dehydrogenation and bc = CndashC bond cleavage Two reactions are not shown water dissociation H2O = H + OH and the electrochemical
reaction H = H+ + eminus
Flowmeter
Air H2
n-Hexadecane
Deionized H2O
Syringe pumps
AD converter
Vaporizer
Galvanostat
Ano
de
Elec
troly
te
Cath
ode
Fume hood
Condensate
Computer
Figure 2 Diagram of a direct n-hexadecane fueled phosphoric acid fuel cell system
of the MEA in the fuel cell A polarization curve showsthe potential difference as a function of current density n-Hexadecane polarization curves were measured Two typesof time-on-stream experiments were performed (H
2O with
n-C16H34
and H2O only) The time-on-stream experiments
were performed at (a) different molar ratios of water to n-hexadecane (b) different current densities and (c) differenttemperatures
The following operating conditions were used Sepa-rate syringe pumps were used to feed both water and n-hexadecane The water flow rate was expressed as a functionof the stoichiometric ratio (SR) of H
2OC16H34
in (2) for
the anode half reaction A constant flow rate of n-hexadecane(02mLh) was used in all experiments The two water flowrates and their stoichiometric ratios were 1mLh (25 lowast SRH2OC16H34
= 80) and 51mLh (129 lowast SR H2OC16H34
=414) Some experiments were performed with only waterbeing fed to the fuel cell The experiments were performedat two temperatures 160∘C and 190∘C
A Hokuto Denko HA-301 Galvanostat was used to adjustthe potential difference between the anode and cathode of thephosphoric acid fuel cell to maintain the chosen current at aconstant value The potential difference was recorded everysecond using a Lab View data logger
4 Journal of Fuels
0010203040506070809
1
0 05 1 15 2 25 3 35 4 45
Pote
ntia
l diff
eren
ce (V
)
New MEA
Reference
Current density (mAcm2)
Figure 3 Polarization curve for a hydrogen fueled PAFC poten-tial difference between the electrodes (Volts) and current density(mAcm2) Open diamonds are data obtained on a newMEA Opensquares are data obtained on an MEA that had been conditionedin previous experiments with low molecular weight hydrocarbons(ethylene propane) Anode hydrogen flow rate = 96mLh Cath-ode air flow rate = 245mLmin Temperature = 160∘C Pressure =1 atm
3 Results and Discussion
Two hydrogenair polarization curves obtained with a PAFCare shown in Figure 3 The upper curve was the firstexperiment performed with a new MEA The lower curvewas measured after some conditioning experiments hadbeen performed with low molecular weight hydrocarbons(ethylene propane) It is an indication of the condition ofthe MEA at the beginning of this investigation and will bereferred to as the Reference polarization curve The opencircuit potential in Figure 3 is about 093V It is comparableto the 09V value reported by Fuller et al [35] with an aircathode half-cell having a hydrogen Reference electrode
The results of two time-on-stream experiments at 160∘Care shown in Figure 4 Both curves show deactivationindicated by a decrease in potential difference with timeThe data show that deactivation continued for at least 20hours The two sets of data were obtained at different currentdensities and different H
2On-C
16H34
molar ratios Thedeactivation reported here with n-hexadecane is consistentwith deactivation reported earlier by Okrent and Heath [36]during direct hydrocarbon fuel cell experiments with decane
Two hypotheses can be suggested to explain deactivationCarbon monoxide a reaction intermediate formed duringthe overall reaction to produce the CO
2 shown in Figure 1
could poison the platinum catalyst at the anode Carbonmonoxide is a well-known poison on fuel cell platinumcatalysts [27] The other possibility is the formation ofcarbonaceous deposits Liebhafsky and Cairns [37] indicatedthe formation of dehydrogenated residues or carbonaceousmaterials during the operation of fuel cells with hydrocarbonfuels
The current densities in Figure 4 were integrated withrespect to time to obtain the cumulative amount of chargetransferred The potential difference in Figure 4 was plotted
Figure 4 Potential difference between the electrodes (V) andtime-on-stream (h) for an n-hexadecane fueled PAFC Anoden-hexadecane flow rate = 02mLh Cathode air flow rate =245mLmin Temperature= 160∘C Pressure = 1 atm Open trianglesare data obtained with current density 119895 = 004mAcm2 water flowrate = 51mLh and H
2On-C
16H34= 129 lowast SR Open squares are
data obtained with current density 119895 = 02mAcm2 water flowrate = 1mLh and H
2On-C
16H34= 25 lowast SR
0
01
02
03
04
05
06
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Pote
ntia
l diff
eren
ce (V
)
Cumulative charge transfer (Ccm2)
H2On-C16H34 = 129 lowast SR
H2On-C16H34 = 25 lowast SR
Figure 5 Potential difference between the electrodes (V) andcumulative charge transfer (Ccm2) for an n-hexadecane PAFCAnode n-hexadecane flow rate = 02mLh Cathode air flow rate =245mLmin Pressure = 1 atm Temperature = 160∘C Open trianglesare data obtained with water flow rate = 51mLh current density =004mAcm2 and H
2On-C
16H34
= 129 lowast SR Open squares aredata obtained with water flow rate = 1mLh current density =02mAcm2 and H
2On-C
16H34= 25 lowast SR
as a function of cumulative charge transferred in Figure 5The data indicate that at potential differences less than04V the slopes of the two lines are the same In otherwords deactivation is a linear function of charge transferredThat observation suggests that deactivation as representedby a decrease in potential difference is related to somephenomenon that correlates with the amount of chargetransferred regardless of the H
2On-C
16H34molar ratio
A hydrogenair polarization curve was measuredusing the PAFC after the first TOS experiment at 160∘C
Journal of Fuels 5
0010203040506070809
1
0 05 1 15 2 25 3 35 4 45
Reference
After 1st TOS experiment
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 6 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Open squaresare the Reference polarization curve Open triangles are the polar-ization curve obtained after the first time-on-stream experiment
(25 lowast SR H2On-C
16H34
= 81) In Figure 6 it is comparedto the ldquoReferencerdquo hydrogenair polarization curve fromFigure 3 The change between the Reference polarizationcurve and the one after the first time-on-stream experimentindicates that there had been a definite deterioration in thefuel cell performance The data in Figure 6 are consistentwith the deactivation observed during the TOS experimentsin Figure 4 If the two polarization curves are compared ata constant value of potential difference the current densityis much smaller after the TOS measurements than beforeEither the turnover frequency on a reaction site is muchsmaller or there are fewer reaction sites at which the reactionoccursThe only explanation is that something has preventedsmall hydrogen molecules from reacting to form electrons
Since deactivation during the TOS experiments wasobserved using both sets of operating conditions at 160∘Cfurther experiments were performed at a temperature of190∘C The MEA was treated by operating sequentially withhydrogen (6 h) water (6 h) and hydrogen (6 h) Then apolarization curve was measured The technique for mea-suring the polarization curve is indicated in Figure 7The current density was set to a constant value Thenthe potential difference was recorded until a steady-statevalue for the potential was obtained For one datum pointcorresponding to 04mAcm2 the steady-state value ofthe potential difference was extrapolated from the datain Figure 7 Generally at least one hour was requiredto obtain a steady-state value for the potential differenceFinally the steady-state values of the potential differencesobtained in Figure 7 were used in Figure 8 to constructa polarization curve for the n-hexadecanewater-air fuelcell
Some of the characteristics of the 190∘C n-hexadecaneairpolarization curve in Figure 8 are noteworthy The opencircuit potential of 05 V is much smaller than that of 093Vobtained for the hydrogenair fuel cell in Figure 3 It suggests
Figure 7 Potential difference between electrodes (V) as a functionof time (h) obtained with a PAFC Anode water flow rate =51mLh n-hexadecane flow rate = 02mLh Cathode air flowrate = 245mLmin Temperature = 190∘C pressure = 1 atm with anH2OC16H34ratio = 129 lowast SR The numbers on the top of each line
represent different current densities
0
01
02
03
04
05
06
0 005 01 015 02 025 03 035 04
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 8 Polarization curve for an n-hexadecane fueled PAFCpotential difference between the electrodes (V) and current density(mAcm2) Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
that the results in Figure 8 might represent the partialoxidation of carbon
C + 12
O2= CO 119864
0
298= 0711V (4)
as the rate limiting step in the overall reaction rather than theoxidation of n-hexadecane in (2) Equation (4) is composedof two half-cell reactions
C +H2O = CO + 2H+ + 2eminus anode (5)
2H+ + 2eminus + 12
O2= H2O cathode (6)
The difference between 0711 V and 05V might becaused by a combination of factors a temperature of 190∘Crather than 25∘C a cathode oxygen mole fraction of 021
6 Journal of Fuels
and an anode water vapour mole fraction representingequilibrium water vapour over phosphoric acid The opencircuit potential 05 V in Figure 8 is more consistent with thestandard electrochemical potential of the partial oxidationof carbon to carbon monoxide reaction 0711 V than withthe standard electrochemical potential of the oxidation ofcarbon monoxide to carbon dioxide (CO + (12)O
2=
CO2 1198640298= 133V) Initially two possible hypotheses were
suggested to explain deactivation either carbon monoxidepoisoning or deposition of carbonaceous material Equation(4) is consistent with the carbonaceous material hypothesisand not consistentwith carbonmonoxide hypothesis On thatbasis the hypothesis of deposition of carbonaceous materialseems to be the most likely explanation for the deactivationobserved during the time-on-stream experiments
Time-on-streammeasurements were also made at 190∘CThe TOS results at 190∘C are compared with those at 160∘Cin Figure 9 A steady-state operation was achieved for thelast six hours of the experiment at 190∘C A steady-stateoperation is a highly desirable result that is not alwaysachieved with a comparatively large hydrocarbon moleculesuch as hexadecane For example Okrent and Heath [36]reported unsteady cycling during which both the potentialand the current oscillated over time periods of approximately15 minutes when octane was the hydrocarbon fuel Althoughwe also observed cycling in some of our experiments thatphenomenon was not the object of our investigationThe factthat a steady-state has been demonstrated here for one set ofoperating conditions means that in principle fuel cells canoperate continuously using n-hexadecane (and presumablyother diesel type fuels)
Cleaning the MEA with water was mentioned in thediscussion pertaining to Figure 7 An example of water beingthe only reactant entering the fuel cell is shown in Figure 10The data in Figure 10 were obtained from an MEA that hadbeen used previously for 10 weeks in TOS experimentsWhenthe current density was maintained constant at a value of02mAcm2 the potential difference decreased continuouslyfor a period of 6 hours That indicated that a progressivelylarger overpotential was necessary (a larger driving force wasnecessary) tomaintain the current density at a constant valueWhen the current density was decreased to 01mAcm2 therewas an initial increase in the potential difference (smalleroverpotential) The potential difference gradually decreasedover the next 7 hours and then remained constant at 035Vfor the last 6 hours
The existence of a current densitywhenonlywaterwas fedto the fuel cell would require that some reaction must havebeen occurring Since no fuel (eg no n-hexadecane) wasfed to the fuel cell it is plausible that the reaction may haveoccurred between water and the carbonaceous material thathad been previously deposited on the MEA The existence ofa current density would also require proton migration acrossthe electrolyte The occurrence of the anode reaction shownin (5) would be consistent with both of these requirementsThe measurement of current density when only water wasfed to the fuel cell is consistent with the hypothesis thatcarbonaceous material was formed during deactivation andwas available for reaction during the water-only experiment
Figure 9 Potential differences between the electrodes (V) and time-on-stream (h) for an n-hexadecane PAFC Current density 119895 =004mAcm2 Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Pressure =1 atm
0
01
02
03
04
05
06
07
0 2 4 6 8 10 12 14 16 18 20Time-on-stream (h)
Pote
ntia
l diff
eren
ce (V
)
j = 02mAcm2j = 01mAcm2
Figure 10 Potential differences between the electrodes (V) as afunction of time-on-stream (h) when H
2O was the only feed stock
for the anode of a PAFC with a fouled MEA Anode water flowrate = 51mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
After the water-only experiments in Figure 10 werecompleted a hydrogen polarization curve was measured Itis compared with the Reference hydrogen polarization curvein Figure 11 A comparison of the results in Figure 11 (after thewater-only experiment) with the results in Figure 6 (after thefirst TOS experiment) indicates that a substantial improve-ment was caused by the water-only treatment That suggeststhe water-only experiment cleaned the MEA Cleaning of theMEA would be consistent with removal of a carbonaceousdeposit from the catalyst surface
The results reported here can be comparedwith other fuelcell systems Two of the important criteria are capital costand energy efficiency The capital cost is strongly influencedby the size of the fuel cell stack that in turn is a function ofcurrent density The theoretical energy efficiency is relatedto the thermodynamic efficiency of the reactions that occur
Journal of Fuels 7
0010203040506070809
1
0 05 1 15 2 25 3 35 4
After water-onlyexperiments
Reference
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 11 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Solid circles aredata obtained after a one-week experiment with water-only (on anMEA that had been used in TOS experiments for ten weeks) Opensquares are data for the Reference polarization curve
The reaction networks that occur vary with the particulartype of fuel cell systemThe operating cost of a fuel cell systemis strongly influenced by the energy efficiency
Small current densities were obtained for the low-temperature (190∘C) direct hydrocarbon (n-hexadecane)PAFC results without a reforming unit reported here Thereare extensive reviews describing results obtained by PAFCsoperating on hydrocarbons without a reforming unit [2ndash4]In general the current densities are quite small Thereforelarge reactors having a large capital cost would be requiredIn contrast Kim et al [38] reported much larger currentdensities using a higher temperature (700∘C) solid oxide fuelcell SOFC without a reforming unit when it was operatingon synthetic diesel fuel Interest in these systems specificallythe development of anodes continues to be an active area ofresearch [39 40] There have been several reviews of directhydrocarbon SOFCs without reforming units [13 41 42]Although no reforming unit was used they indicate thatinternal reforming occurs [13] Unfortunately the reformingreaction (internal or external) has a negative effect onenergy efficiency Approximately 25 of the hydrocarbonfuel must be used to provide the endothermic heat ofreaction for the reforming reaction At the low temperaturesused in this study the reforming reaction is thermodynam-ically unfavourable and does not occur Therefore the high-temperature SOFC systems will have a capital cost advantageover the lower temperature PAFC systemused here Howeverthe lower temperature PAFC system used here will havea theoretical energy efficiency advantage over the SOFCsystem
The use of an external reformer in combination with aPAFC system is a well-established technology that convertsthe hydrocarbon to hydrogen in a fuel processing system andthen uses the hydrogen as the fuel in a fuel cell system Bythe year 2006 more than 200 commercial plants had beensold [43] Nevertheless research on improving the reforming
process continues [44]The reforming reaction in an externalreformer has the same negative effect on energy efficiencythat was mentioned above for internal reforming The fuelprocessing system includes four processes steam reforminghigh-temperature water shift low-temperature shift andhydrogen purification Equipment for those four processeshas a substantial capital cost In contrast there is no capitalcost for a reformerfuel processor with the low-temperaturedirect hydrocarbon PAFC system described here
4 Conclusions
This study reported the first polarization curve evermeasuredforwhich n-hexadecanewas the fuel at the anode of a fuel cellThe current densities were found to be very small
Deactivation was observed in time-on-stream experi-ments Deactivation as measured by the change in potentialdifference was found to be a linear function of the cumulativecharge transferred across the electrolyte of the fuel cellDeactivation during fuel cell experiments with n-hexadecanewas confirmed by comparing hydrogen polarization curvesbefore and after the time-on-stream measurements For agiven potential difference the current densities were muchsmaller for the hydrogen polarization curves measured afterthe time-on-stream experiments
Experiments were performed in whichwater was the onlyreactant entering the fuel cell that had been used previouslyfor 10 weeks in time-on-stream experiments Current den-sities were measured during those experiments indicatingthat the water must have reacted with some type of speciesthat remained on the fuel cell catalyst at the end of thetime-on-stream experiments When a hydrogen polarizationcurvewasmeasured at the end of thewater-only experimentsit was close to that measured before the time-on-streamexperiments That indicates that the deactivating species onthe surface of the platinum particles had been removed andthat it was possible to regenerate deactivated MEAs
A hypothesis that carbonaceous material was depositedon the platinum anode catalyst particles was suggested toexplain the deactivation Four types of observations wereconsistent with that hypothesis (a) the change in potentialdifference during time-on-stream measurements (b) whenhydrogen polarization curves measured before and after thetime-on-stream experiments were compared the currentdensities measured after TOS were much smaller than thosemeasured before TOS (c) current densities were measuredwhen water was the only reactant entering the fuel cell Inorder to produce a current density water must have reactedwith some type of species that had been deposited on thesurface of the platinum particles and (d) the open circuitpotential of a n-hexadecane fuel cell 05 V was much closerto the standard electrochemical potential for the carbon-water reaction 0711 V than to that for the carbonmonoxide-water reaction 133 V Observation (d) makes a hypothesisof deactivation by carbonaceous materials more likely thandeactivation by carbon monoxide poisoning
Steady-state operation of the n-hexadecane fuel cellwithout additional deactivation was observed at one set of
8 Journal of Fuels
fuel cell operating conditionsThat observation demonstratesthat stable fuel cell operation is technically feasible whenn-hexadecane is the fuel at the anode of a fuel cell Itsuggests there ismerit in investigating fuel cell operationwithcommercial fuels such as petroleum diesel or biodiesel
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this research anddevelopment project was supported by a grant from Trans-port Canadarsquos Clean Rail Academic Grant Program and bya Discovery Grant from the Canadian Governmentrsquos NaturalSciences and Engineering Research Council
References
[1] J A A Ketelaar ldquoHistoryrdquo in Fuel Cell Systems L JM J Blomenand M N Mugerwa Eds p 20 Plenum Press New York NYUSA 1993
[2] E J Cairns ldquoAnodic oxidation of hydrocarbons and thehydrocarbon fuel cellrdquoAdvances in Electrochemistry Science andElectrochemical Engineering vol 8 pp 337ndash392 1971
[3] J O M Bockris and S Srinivasan ldquoElectrochemical combus-tion of organic substancesrdquo in Fuel CellsTheir Electrochemistrypp 357ndash411 McGraw-Hill New York NY USA 1969
[4] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 458ndash523 John Wiley amp Sons New York NY USA 1968
[5] S Bertholet Oxydation Electrocatalytique du Methane [PhDDissertation] Universite de Poitiers Poitiers France 1998
[6] C K Cheng J L Luo K T Chuang and A R SangerldquoPropane fuel cells using phosphoric-acid-doped polybenzim-idazole membranesrdquo The Journal of Physical Chemistry B vol109 no 26 pp 13036ndash13042 2005
[7] O Savadogo and F J Rodriguez Varela ldquoLow-temperaturedirect propane polymer electrolyte membranes fuel cellrdquo Jour-nal of New Materials for Electrochemical Systems vol 4 no 2pp 93ndash97 2001
[8] F J Rodrıguez Varela and O Savadogo ldquoReal-time massspectrometric analysis of the anode exhaust gases of a directpropane fuel cellrdquo Journal of the Electrochemical Society vol 152no 9 pp A1755ndashA1762 2005
[9] P Heo K Ito A Tomita and T Hibino ldquoA proton-conductingfuel cell operating with hydrocarbon fuelsrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7841ndash78442008
[10] B C H Steele I Kelly H Middleton and R Rudkin ldquoOxida-tion of methane in solid state electrochemical reactorsrdquo SolidState Ionics vol 28ndash30 no 2 pp 1547ndash1552 1988
[11] E P Murray T Tsai and S A Barnett ldquoA direct-methane fuelcell with a ceria-based anoderdquo Nature vol 400 no 6745 pp649ndash651 1999
[12] W Zhu C Xia J Fan R Peng and G Meng ldquoCeria coated Nias anodes for direct utilization of methane in low-temperature
solid oxide fuel cellsrdquo Journal of Power Sources vol 160 no 2pp 897ndash902 2006
[13] M D Gross J M Vohs and R J Gorte ldquoRecent progress inSOFC anodes for direct utilization of hydrocarbonsrdquo Journal ofMaterials Chemistry vol 17 no 30 pp 3071ndash3077 2007
[14] J G Lee C M Lee M Park and Y G Shul ldquoDirect methanefuel cell with La
2Sn2O7ndashNindashGd
01Ce09O195
anode and electro-spun La
06Sr04Co02Fe08O3minus120575
ndashGd01Ce09O195
cathoderdquo RoyalSociety of Chemistry Advances vol 3 no 29 pp 11816ndash118222013
[15] D Ding Z Liu L Li andC Xia ldquoAn octane-fueled low temper-ature solid oxide fuel cell with Ru-free anodesrdquo ElectrochemistryCommunications vol 10 no 9 pp 1295ndash1298 2008
[16] H Kishimoto K Yamaji T Horita et al ldquoFeasibility of liquidhydrocarbon fuels for SOFC with Ni-ScSZ anoderdquo Journal ofPower Sources vol 172 no 1 pp 67ndash71 2007
[17] Z F Zhou C Gallo M B Pague H Schobert and S N LvovldquoDirect oxidation of jet fuels and Pennsylvania crude oil in asolid oxide fuel cellrdquo Journal of Power Sources vol 133 no 2 pp181ndash187 2004
[18] G Psofogiannakis Y Bourgault B E Conway and M TernanldquoMathematical model for a direct propane phosphoric acid fuelcellrdquo Journal of Applied Electrochemistry vol 36 no 1 pp 115ndash130 2006
[19] H Khakdaman Y Bourgault and M Ternan ldquoComputationalmodeling of a direct propane fuel cellrdquo Journal of Power Sourcesvol 196 no 6 pp 3186ndash3194 2011
[20] H R Khakdaman Y Bourgault and M Ternan ldquoDirectpropane fuel cell anode with interdigitated flow fields two-dimensional modelrdquo Industrial amp Engineering ChemistryResearch vol 49 no 3 pp 1079ndash1085 2010
[21] G Psofogiannakis A St-Amant andM Ternan ldquoAb-initioDFTstudy of methane electro-oxidation mechanism on platinumrdquoJournal of Physical Chemistry B vol 110 pp 24593ndash24605 2006
[22] S Vafaeyan A St-Amant andM Ternan ldquoNickel alloy catalystsfor the anode of a high temperature PEM direct propane fuelcellrdquo Journal of Chemistry vol 2014 Article ID 151638 8 pages2014
[23] S Vafaeyan A St-Amant and M Ternan ldquoPropane fuel cellsselectivity for partial or complete reactionrdquo Journal of Fuels vol2014 Article ID 485045 9 pages 2014
[24] A Al-Othman A Y Tremblay W Pell et al ldquoA modified silicicacid (Si) and sulphuric acid (S)-ZrPPTFEglycerol compositemembrane for high temperature direct hydrocarbon fuel cellsrdquoJournal of Power Sources vol 224 pp 158ndash167 2013
[25] A Al-Othman A Y Tremblay W Pell Y Liu B A Peppleyand M Ternan ldquoThe effect of glycerol on the conductivity ofNafion-free ZrPPTFE composite membrane electrolytes fordirect hydrocarbon fuel cellsrdquo Journal of Power Sources vol 199pp 14ndash21 2012
[26] A Al-Othman A Y Tremblay W Pell et al ldquoZirconium phos-phate as the proton conducting material in direct hydrocarbonpolymer electrolyte membrane fuel cells operating above theboiling point of waterrdquo Journal of Power Sources vol 195 no9 pp 2520ndash2525 2010
[27] C G Farrell C L Gardner and M Ternan ldquoExperimental andmodelling studies of CO poisoning in PEM fuel cellsrdquo Journalof Power Sources vol 171 no 2 pp 282ndash293 2007
[28] R Fonocho C L Gardner and M Ternan ldquoA study of theelectrochemical hydrogenation of o-xylene in a PEM hydro-genation reactorrdquo Electrochimica Acta vol 75 pp 171ndash178 2012
Journal of Fuels 9
[29] N Sammes R Bove and K Stahl ldquoPhosphoric acid fuel cellsfundamentals and applicationsrdquo Current Opinion in Solid Stateand Materials Science vol 8 no 5 pp 372ndash378 2004
[30] J M King and H R Kunz ldquoPhosphoric acid electrolyte fuelcellsrdquo in Handbook of Fuel Cells W Vielstich A Lamm HA Gasteiger and H Yokokawa Eds vol 1 pp 287ndash300 JohnWiley amp Sons New York NY USA 2010
[31] S R Choudhury ldquoPhosphoric acid fuel cell technologyrdquo inRecent Trends in Fuel Cell Science and Technology S Basu Edpp 188ndash216 Springer New York NY USA 2007
[32] W Grubb and C J Michalske ldquoA high performance propanefuel cell operating in the temperature range of 150∘ndash200∘CrdquoJournal of The Electrochemical Society vol 111 no 9 p 10151964
[33] H A Liebhafsky andW T Grubb ldquoNormal alkanes at platinumanodesrdquo Fuel Preprints vol 11 no 2 p 134 1967
[34] V S Bagotzky Y B Vassiliev and O A Khazova ldquoGeneralizedscheme of chemisorption electrooxidation and electroreduc-tion of simple organic compounds on platinum group metalsrdquoJournal of Electroanalytical Chemistry and Interfacial Electro-chemistry vol 81 no 2 pp 229ndash238 1977
[35] T F Fuller F J Luczak and D J Wheeler ldquoElectrocatalystutilization in phosphoric acid fuel cellsrdquo Journal of the Electro-chemical Society vol 142 no 6 pp 1752ndash1757 1995
[36] E H Okrent and C E Heath ldquoA liquid hydrocarbon fuel cellbatteryrdquo in Fuel Cell Systems B Baker Ed Advances in Chem-istry pp 328ndash340 American Chemical Society WashingtonDC USA 1969
[37] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 485ndash510 John Wiley amp Sons New York NY USA 1968
[38] H Kim S Park J M Vohs and R J Gorte ldquoDirect oxidationof liquid fuels in a solid oxide fuel cellrdquo Journal of the Electro-chemical Society vol 148 no 7 pp A693ndashA695 2001
[39] S Islam and J M Hill ldquoBarium oxide promoted NiYSZ solid-oxide fuel cells for direct utilization of methanerdquo Journal ofMaterials Chemistry A vol 2 no 6 pp 1922ndash1929 2014
[40] C Yang J Li Y Lin J Liu F Chen and M Liu ldquoIn-situfabrication of CoFe allot nanoparticles structure (Pr
04Sr06)3
(Fe085
Nb015
)O7ceramic anode for direct hydrocarbon solid
oxde fuel cellsrdquo Nano Energy vol 11 pp 704ndash711 2015[41] S McIntosh and R J Gorte ldquoDirect hydrocarbon solid oxide
fuel cellsrdquo Chemical Reviews vol 104 no 10 pp 4845ndash48652004
[42] Y Zhao C Xia L Jia et al ldquoRecent progress on solid oxide fuelcell lowering temperature and utilizing non-hydrogen fuelsrdquoInternational Journal of Hydrogen Energy vol 38 no 36 pp16498ndash16517 2013
[43] S Srinivasan Fuel Cells From Fundamentals to ApplicationsSpringer New York NY USA 2006
[44] M RWalluk J LinMGWaller D F Smith andTA TraboldldquoDiesel auto-thermal reforming for solid oxide fuel cell systemsanode off-gas recycle simulationrdquo Applied Energy vol 130 pp94ndash102 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
4 Journal of Fuels
0010203040506070809
1
0 05 1 15 2 25 3 35 4 45
Pote
ntia
l diff
eren
ce (V
)
New MEA
Reference
Current density (mAcm2)
Figure 3 Polarization curve for a hydrogen fueled PAFC poten-tial difference between the electrodes (Volts) and current density(mAcm2) Open diamonds are data obtained on a newMEA Opensquares are data obtained on an MEA that had been conditionedin previous experiments with low molecular weight hydrocarbons(ethylene propane) Anode hydrogen flow rate = 96mLh Cath-ode air flow rate = 245mLmin Temperature = 160∘C Pressure =1 atm
3 Results and Discussion
Two hydrogenair polarization curves obtained with a PAFCare shown in Figure 3 The upper curve was the firstexperiment performed with a new MEA The lower curvewas measured after some conditioning experiments hadbeen performed with low molecular weight hydrocarbons(ethylene propane) It is an indication of the condition ofthe MEA at the beginning of this investigation and will bereferred to as the Reference polarization curve The opencircuit potential in Figure 3 is about 093V It is comparableto the 09V value reported by Fuller et al [35] with an aircathode half-cell having a hydrogen Reference electrode
The results of two time-on-stream experiments at 160∘Care shown in Figure 4 Both curves show deactivationindicated by a decrease in potential difference with timeThe data show that deactivation continued for at least 20hours The two sets of data were obtained at different currentdensities and different H
2On-C
16H34
molar ratios Thedeactivation reported here with n-hexadecane is consistentwith deactivation reported earlier by Okrent and Heath [36]during direct hydrocarbon fuel cell experiments with decane
Two hypotheses can be suggested to explain deactivationCarbon monoxide a reaction intermediate formed duringthe overall reaction to produce the CO
2 shown in Figure 1
could poison the platinum catalyst at the anode Carbonmonoxide is a well-known poison on fuel cell platinumcatalysts [27] The other possibility is the formation ofcarbonaceous deposits Liebhafsky and Cairns [37] indicatedthe formation of dehydrogenated residues or carbonaceousmaterials during the operation of fuel cells with hydrocarbonfuels
The current densities in Figure 4 were integrated withrespect to time to obtain the cumulative amount of chargetransferred The potential difference in Figure 4 was plotted
Figure 4 Potential difference between the electrodes (V) andtime-on-stream (h) for an n-hexadecane fueled PAFC Anoden-hexadecane flow rate = 02mLh Cathode air flow rate =245mLmin Temperature= 160∘C Pressure = 1 atm Open trianglesare data obtained with current density 119895 = 004mAcm2 water flowrate = 51mLh and H
2On-C
16H34= 129 lowast SR Open squares are
data obtained with current density 119895 = 02mAcm2 water flowrate = 1mLh and H
2On-C
16H34= 25 lowast SR
0
01
02
03
04
05
06
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Pote
ntia
l diff
eren
ce (V
)
Cumulative charge transfer (Ccm2)
H2On-C16H34 = 129 lowast SR
H2On-C16H34 = 25 lowast SR
Figure 5 Potential difference between the electrodes (V) andcumulative charge transfer (Ccm2) for an n-hexadecane PAFCAnode n-hexadecane flow rate = 02mLh Cathode air flow rate =245mLmin Pressure = 1 atm Temperature = 160∘C Open trianglesare data obtained with water flow rate = 51mLh current density =004mAcm2 and H
2On-C
16H34
= 129 lowast SR Open squares aredata obtained with water flow rate = 1mLh current density =02mAcm2 and H
2On-C
16H34= 25 lowast SR
as a function of cumulative charge transferred in Figure 5The data indicate that at potential differences less than04V the slopes of the two lines are the same In otherwords deactivation is a linear function of charge transferredThat observation suggests that deactivation as representedby a decrease in potential difference is related to somephenomenon that correlates with the amount of chargetransferred regardless of the H
2On-C
16H34molar ratio
A hydrogenair polarization curve was measuredusing the PAFC after the first TOS experiment at 160∘C
Journal of Fuels 5
0010203040506070809
1
0 05 1 15 2 25 3 35 4 45
Reference
After 1st TOS experiment
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 6 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Open squaresare the Reference polarization curve Open triangles are the polar-ization curve obtained after the first time-on-stream experiment
(25 lowast SR H2On-C
16H34
= 81) In Figure 6 it is comparedto the ldquoReferencerdquo hydrogenair polarization curve fromFigure 3 The change between the Reference polarizationcurve and the one after the first time-on-stream experimentindicates that there had been a definite deterioration in thefuel cell performance The data in Figure 6 are consistentwith the deactivation observed during the TOS experimentsin Figure 4 If the two polarization curves are compared ata constant value of potential difference the current densityis much smaller after the TOS measurements than beforeEither the turnover frequency on a reaction site is muchsmaller or there are fewer reaction sites at which the reactionoccursThe only explanation is that something has preventedsmall hydrogen molecules from reacting to form electrons
Since deactivation during the TOS experiments wasobserved using both sets of operating conditions at 160∘Cfurther experiments were performed at a temperature of190∘C The MEA was treated by operating sequentially withhydrogen (6 h) water (6 h) and hydrogen (6 h) Then apolarization curve was measured The technique for mea-suring the polarization curve is indicated in Figure 7The current density was set to a constant value Thenthe potential difference was recorded until a steady-statevalue for the potential was obtained For one datum pointcorresponding to 04mAcm2 the steady-state value ofthe potential difference was extrapolated from the datain Figure 7 Generally at least one hour was requiredto obtain a steady-state value for the potential differenceFinally the steady-state values of the potential differencesobtained in Figure 7 were used in Figure 8 to constructa polarization curve for the n-hexadecanewater-air fuelcell
Some of the characteristics of the 190∘C n-hexadecaneairpolarization curve in Figure 8 are noteworthy The opencircuit potential of 05 V is much smaller than that of 093Vobtained for the hydrogenair fuel cell in Figure 3 It suggests
Figure 7 Potential difference between electrodes (V) as a functionof time (h) obtained with a PAFC Anode water flow rate =51mLh n-hexadecane flow rate = 02mLh Cathode air flowrate = 245mLmin Temperature = 190∘C pressure = 1 atm with anH2OC16H34ratio = 129 lowast SR The numbers on the top of each line
represent different current densities
0
01
02
03
04
05
06
0 005 01 015 02 025 03 035 04
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 8 Polarization curve for an n-hexadecane fueled PAFCpotential difference between the electrodes (V) and current density(mAcm2) Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
that the results in Figure 8 might represent the partialoxidation of carbon
C + 12
O2= CO 119864
0
298= 0711V (4)
as the rate limiting step in the overall reaction rather than theoxidation of n-hexadecane in (2) Equation (4) is composedof two half-cell reactions
C +H2O = CO + 2H+ + 2eminus anode (5)
2H+ + 2eminus + 12
O2= H2O cathode (6)
The difference between 0711 V and 05V might becaused by a combination of factors a temperature of 190∘Crather than 25∘C a cathode oxygen mole fraction of 021
6 Journal of Fuels
and an anode water vapour mole fraction representingequilibrium water vapour over phosphoric acid The opencircuit potential 05 V in Figure 8 is more consistent with thestandard electrochemical potential of the partial oxidationof carbon to carbon monoxide reaction 0711 V than withthe standard electrochemical potential of the oxidation ofcarbon monoxide to carbon dioxide (CO + (12)O
2=
CO2 1198640298= 133V) Initially two possible hypotheses were
suggested to explain deactivation either carbon monoxidepoisoning or deposition of carbonaceous material Equation(4) is consistent with the carbonaceous material hypothesisand not consistentwith carbonmonoxide hypothesis On thatbasis the hypothesis of deposition of carbonaceous materialseems to be the most likely explanation for the deactivationobserved during the time-on-stream experiments
Time-on-streammeasurements were also made at 190∘CThe TOS results at 190∘C are compared with those at 160∘Cin Figure 9 A steady-state operation was achieved for thelast six hours of the experiment at 190∘C A steady-stateoperation is a highly desirable result that is not alwaysachieved with a comparatively large hydrocarbon moleculesuch as hexadecane For example Okrent and Heath [36]reported unsteady cycling during which both the potentialand the current oscillated over time periods of approximately15 minutes when octane was the hydrocarbon fuel Althoughwe also observed cycling in some of our experiments thatphenomenon was not the object of our investigationThe factthat a steady-state has been demonstrated here for one set ofoperating conditions means that in principle fuel cells canoperate continuously using n-hexadecane (and presumablyother diesel type fuels)
Cleaning the MEA with water was mentioned in thediscussion pertaining to Figure 7 An example of water beingthe only reactant entering the fuel cell is shown in Figure 10The data in Figure 10 were obtained from an MEA that hadbeen used previously for 10 weeks in TOS experimentsWhenthe current density was maintained constant at a value of02mAcm2 the potential difference decreased continuouslyfor a period of 6 hours That indicated that a progressivelylarger overpotential was necessary (a larger driving force wasnecessary) tomaintain the current density at a constant valueWhen the current density was decreased to 01mAcm2 therewas an initial increase in the potential difference (smalleroverpotential) The potential difference gradually decreasedover the next 7 hours and then remained constant at 035Vfor the last 6 hours
The existence of a current densitywhenonlywaterwas fedto the fuel cell would require that some reaction must havebeen occurring Since no fuel (eg no n-hexadecane) wasfed to the fuel cell it is plausible that the reaction may haveoccurred between water and the carbonaceous material thathad been previously deposited on the MEA The existence ofa current density would also require proton migration acrossthe electrolyte The occurrence of the anode reaction shownin (5) would be consistent with both of these requirementsThe measurement of current density when only water wasfed to the fuel cell is consistent with the hypothesis thatcarbonaceous material was formed during deactivation andwas available for reaction during the water-only experiment
Figure 9 Potential differences between the electrodes (V) and time-on-stream (h) for an n-hexadecane PAFC Current density 119895 =004mAcm2 Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Pressure =1 atm
0
01
02
03
04
05
06
07
0 2 4 6 8 10 12 14 16 18 20Time-on-stream (h)
Pote
ntia
l diff
eren
ce (V
)
j = 02mAcm2j = 01mAcm2
Figure 10 Potential differences between the electrodes (V) as afunction of time-on-stream (h) when H
2O was the only feed stock
for the anode of a PAFC with a fouled MEA Anode water flowrate = 51mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
After the water-only experiments in Figure 10 werecompleted a hydrogen polarization curve was measured Itis compared with the Reference hydrogen polarization curvein Figure 11 A comparison of the results in Figure 11 (after thewater-only experiment) with the results in Figure 6 (after thefirst TOS experiment) indicates that a substantial improve-ment was caused by the water-only treatment That suggeststhe water-only experiment cleaned the MEA Cleaning of theMEA would be consistent with removal of a carbonaceousdeposit from the catalyst surface
The results reported here can be comparedwith other fuelcell systems Two of the important criteria are capital costand energy efficiency The capital cost is strongly influencedby the size of the fuel cell stack that in turn is a function ofcurrent density The theoretical energy efficiency is relatedto the thermodynamic efficiency of the reactions that occur
Journal of Fuels 7
0010203040506070809
1
0 05 1 15 2 25 3 35 4
After water-onlyexperiments
Reference
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 11 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Solid circles aredata obtained after a one-week experiment with water-only (on anMEA that had been used in TOS experiments for ten weeks) Opensquares are data for the Reference polarization curve
The reaction networks that occur vary with the particulartype of fuel cell systemThe operating cost of a fuel cell systemis strongly influenced by the energy efficiency
Small current densities were obtained for the low-temperature (190∘C) direct hydrocarbon (n-hexadecane)PAFC results without a reforming unit reported here Thereare extensive reviews describing results obtained by PAFCsoperating on hydrocarbons without a reforming unit [2ndash4]In general the current densities are quite small Thereforelarge reactors having a large capital cost would be requiredIn contrast Kim et al [38] reported much larger currentdensities using a higher temperature (700∘C) solid oxide fuelcell SOFC without a reforming unit when it was operatingon synthetic diesel fuel Interest in these systems specificallythe development of anodes continues to be an active area ofresearch [39 40] There have been several reviews of directhydrocarbon SOFCs without reforming units [13 41 42]Although no reforming unit was used they indicate thatinternal reforming occurs [13] Unfortunately the reformingreaction (internal or external) has a negative effect onenergy efficiency Approximately 25 of the hydrocarbonfuel must be used to provide the endothermic heat ofreaction for the reforming reaction At the low temperaturesused in this study the reforming reaction is thermodynam-ically unfavourable and does not occur Therefore the high-temperature SOFC systems will have a capital cost advantageover the lower temperature PAFC systemused here Howeverthe lower temperature PAFC system used here will havea theoretical energy efficiency advantage over the SOFCsystem
The use of an external reformer in combination with aPAFC system is a well-established technology that convertsthe hydrocarbon to hydrogen in a fuel processing system andthen uses the hydrogen as the fuel in a fuel cell system Bythe year 2006 more than 200 commercial plants had beensold [43] Nevertheless research on improving the reforming
process continues [44]The reforming reaction in an externalreformer has the same negative effect on energy efficiencythat was mentioned above for internal reforming The fuelprocessing system includes four processes steam reforminghigh-temperature water shift low-temperature shift andhydrogen purification Equipment for those four processeshas a substantial capital cost In contrast there is no capitalcost for a reformerfuel processor with the low-temperaturedirect hydrocarbon PAFC system described here
4 Conclusions
This study reported the first polarization curve evermeasuredforwhich n-hexadecanewas the fuel at the anode of a fuel cellThe current densities were found to be very small
Deactivation was observed in time-on-stream experi-ments Deactivation as measured by the change in potentialdifference was found to be a linear function of the cumulativecharge transferred across the electrolyte of the fuel cellDeactivation during fuel cell experiments with n-hexadecanewas confirmed by comparing hydrogen polarization curvesbefore and after the time-on-stream measurements For agiven potential difference the current densities were muchsmaller for the hydrogen polarization curves measured afterthe time-on-stream experiments
Experiments were performed in whichwater was the onlyreactant entering the fuel cell that had been used previouslyfor 10 weeks in time-on-stream experiments Current den-sities were measured during those experiments indicatingthat the water must have reacted with some type of speciesthat remained on the fuel cell catalyst at the end of thetime-on-stream experiments When a hydrogen polarizationcurvewasmeasured at the end of thewater-only experimentsit was close to that measured before the time-on-streamexperiments That indicates that the deactivating species onthe surface of the platinum particles had been removed andthat it was possible to regenerate deactivated MEAs
A hypothesis that carbonaceous material was depositedon the platinum anode catalyst particles was suggested toexplain the deactivation Four types of observations wereconsistent with that hypothesis (a) the change in potentialdifference during time-on-stream measurements (b) whenhydrogen polarization curves measured before and after thetime-on-stream experiments were compared the currentdensities measured after TOS were much smaller than thosemeasured before TOS (c) current densities were measuredwhen water was the only reactant entering the fuel cell Inorder to produce a current density water must have reactedwith some type of species that had been deposited on thesurface of the platinum particles and (d) the open circuitpotential of a n-hexadecane fuel cell 05 V was much closerto the standard electrochemical potential for the carbon-water reaction 0711 V than to that for the carbonmonoxide-water reaction 133 V Observation (d) makes a hypothesisof deactivation by carbonaceous materials more likely thandeactivation by carbon monoxide poisoning
Steady-state operation of the n-hexadecane fuel cellwithout additional deactivation was observed at one set of
8 Journal of Fuels
fuel cell operating conditionsThat observation demonstratesthat stable fuel cell operation is technically feasible whenn-hexadecane is the fuel at the anode of a fuel cell Itsuggests there ismerit in investigating fuel cell operationwithcommercial fuels such as petroleum diesel or biodiesel
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this research anddevelopment project was supported by a grant from Trans-port Canadarsquos Clean Rail Academic Grant Program and bya Discovery Grant from the Canadian Governmentrsquos NaturalSciences and Engineering Research Council
References
[1] J A A Ketelaar ldquoHistoryrdquo in Fuel Cell Systems L JM J Blomenand M N Mugerwa Eds p 20 Plenum Press New York NYUSA 1993
[2] E J Cairns ldquoAnodic oxidation of hydrocarbons and thehydrocarbon fuel cellrdquoAdvances in Electrochemistry Science andElectrochemical Engineering vol 8 pp 337ndash392 1971
[3] J O M Bockris and S Srinivasan ldquoElectrochemical combus-tion of organic substancesrdquo in Fuel CellsTheir Electrochemistrypp 357ndash411 McGraw-Hill New York NY USA 1969
[4] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 458ndash523 John Wiley amp Sons New York NY USA 1968
[5] S Bertholet Oxydation Electrocatalytique du Methane [PhDDissertation] Universite de Poitiers Poitiers France 1998
[6] C K Cheng J L Luo K T Chuang and A R SangerldquoPropane fuel cells using phosphoric-acid-doped polybenzim-idazole membranesrdquo The Journal of Physical Chemistry B vol109 no 26 pp 13036ndash13042 2005
[7] O Savadogo and F J Rodriguez Varela ldquoLow-temperaturedirect propane polymer electrolyte membranes fuel cellrdquo Jour-nal of New Materials for Electrochemical Systems vol 4 no 2pp 93ndash97 2001
[8] F J Rodrıguez Varela and O Savadogo ldquoReal-time massspectrometric analysis of the anode exhaust gases of a directpropane fuel cellrdquo Journal of the Electrochemical Society vol 152no 9 pp A1755ndashA1762 2005
[9] P Heo K Ito A Tomita and T Hibino ldquoA proton-conductingfuel cell operating with hydrocarbon fuelsrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7841ndash78442008
[10] B C H Steele I Kelly H Middleton and R Rudkin ldquoOxida-tion of methane in solid state electrochemical reactorsrdquo SolidState Ionics vol 28ndash30 no 2 pp 1547ndash1552 1988
[11] E P Murray T Tsai and S A Barnett ldquoA direct-methane fuelcell with a ceria-based anoderdquo Nature vol 400 no 6745 pp649ndash651 1999
[12] W Zhu C Xia J Fan R Peng and G Meng ldquoCeria coated Nias anodes for direct utilization of methane in low-temperature
solid oxide fuel cellsrdquo Journal of Power Sources vol 160 no 2pp 897ndash902 2006
[13] M D Gross J M Vohs and R J Gorte ldquoRecent progress inSOFC anodes for direct utilization of hydrocarbonsrdquo Journal ofMaterials Chemistry vol 17 no 30 pp 3071ndash3077 2007
[14] J G Lee C M Lee M Park and Y G Shul ldquoDirect methanefuel cell with La
2Sn2O7ndashNindashGd
01Ce09O195
anode and electro-spun La
06Sr04Co02Fe08O3minus120575
ndashGd01Ce09O195
cathoderdquo RoyalSociety of Chemistry Advances vol 3 no 29 pp 11816ndash118222013
[15] D Ding Z Liu L Li andC Xia ldquoAn octane-fueled low temper-ature solid oxide fuel cell with Ru-free anodesrdquo ElectrochemistryCommunications vol 10 no 9 pp 1295ndash1298 2008
[16] H Kishimoto K Yamaji T Horita et al ldquoFeasibility of liquidhydrocarbon fuels for SOFC with Ni-ScSZ anoderdquo Journal ofPower Sources vol 172 no 1 pp 67ndash71 2007
[17] Z F Zhou C Gallo M B Pague H Schobert and S N LvovldquoDirect oxidation of jet fuels and Pennsylvania crude oil in asolid oxide fuel cellrdquo Journal of Power Sources vol 133 no 2 pp181ndash187 2004
[18] G Psofogiannakis Y Bourgault B E Conway and M TernanldquoMathematical model for a direct propane phosphoric acid fuelcellrdquo Journal of Applied Electrochemistry vol 36 no 1 pp 115ndash130 2006
[19] H Khakdaman Y Bourgault and M Ternan ldquoComputationalmodeling of a direct propane fuel cellrdquo Journal of Power Sourcesvol 196 no 6 pp 3186ndash3194 2011
[20] H R Khakdaman Y Bourgault and M Ternan ldquoDirectpropane fuel cell anode with interdigitated flow fields two-dimensional modelrdquo Industrial amp Engineering ChemistryResearch vol 49 no 3 pp 1079ndash1085 2010
[21] G Psofogiannakis A St-Amant andM Ternan ldquoAb-initioDFTstudy of methane electro-oxidation mechanism on platinumrdquoJournal of Physical Chemistry B vol 110 pp 24593ndash24605 2006
[22] S Vafaeyan A St-Amant andM Ternan ldquoNickel alloy catalystsfor the anode of a high temperature PEM direct propane fuelcellrdquo Journal of Chemistry vol 2014 Article ID 151638 8 pages2014
[23] S Vafaeyan A St-Amant and M Ternan ldquoPropane fuel cellsselectivity for partial or complete reactionrdquo Journal of Fuels vol2014 Article ID 485045 9 pages 2014
[24] A Al-Othman A Y Tremblay W Pell et al ldquoA modified silicicacid (Si) and sulphuric acid (S)-ZrPPTFEglycerol compositemembrane for high temperature direct hydrocarbon fuel cellsrdquoJournal of Power Sources vol 224 pp 158ndash167 2013
[25] A Al-Othman A Y Tremblay W Pell Y Liu B A Peppleyand M Ternan ldquoThe effect of glycerol on the conductivity ofNafion-free ZrPPTFE composite membrane electrolytes fordirect hydrocarbon fuel cellsrdquo Journal of Power Sources vol 199pp 14ndash21 2012
[26] A Al-Othman A Y Tremblay W Pell et al ldquoZirconium phos-phate as the proton conducting material in direct hydrocarbonpolymer electrolyte membrane fuel cells operating above theboiling point of waterrdquo Journal of Power Sources vol 195 no9 pp 2520ndash2525 2010
[27] C G Farrell C L Gardner and M Ternan ldquoExperimental andmodelling studies of CO poisoning in PEM fuel cellsrdquo Journalof Power Sources vol 171 no 2 pp 282ndash293 2007
[28] R Fonocho C L Gardner and M Ternan ldquoA study of theelectrochemical hydrogenation of o-xylene in a PEM hydro-genation reactorrdquo Electrochimica Acta vol 75 pp 171ndash178 2012
Journal of Fuels 9
[29] N Sammes R Bove and K Stahl ldquoPhosphoric acid fuel cellsfundamentals and applicationsrdquo Current Opinion in Solid Stateand Materials Science vol 8 no 5 pp 372ndash378 2004
[30] J M King and H R Kunz ldquoPhosphoric acid electrolyte fuelcellsrdquo in Handbook of Fuel Cells W Vielstich A Lamm HA Gasteiger and H Yokokawa Eds vol 1 pp 287ndash300 JohnWiley amp Sons New York NY USA 2010
[31] S R Choudhury ldquoPhosphoric acid fuel cell technologyrdquo inRecent Trends in Fuel Cell Science and Technology S Basu Edpp 188ndash216 Springer New York NY USA 2007
[32] W Grubb and C J Michalske ldquoA high performance propanefuel cell operating in the temperature range of 150∘ndash200∘CrdquoJournal of The Electrochemical Society vol 111 no 9 p 10151964
[33] H A Liebhafsky andW T Grubb ldquoNormal alkanes at platinumanodesrdquo Fuel Preprints vol 11 no 2 p 134 1967
[34] V S Bagotzky Y B Vassiliev and O A Khazova ldquoGeneralizedscheme of chemisorption electrooxidation and electroreduc-tion of simple organic compounds on platinum group metalsrdquoJournal of Electroanalytical Chemistry and Interfacial Electro-chemistry vol 81 no 2 pp 229ndash238 1977
[35] T F Fuller F J Luczak and D J Wheeler ldquoElectrocatalystutilization in phosphoric acid fuel cellsrdquo Journal of the Electro-chemical Society vol 142 no 6 pp 1752ndash1757 1995
[36] E H Okrent and C E Heath ldquoA liquid hydrocarbon fuel cellbatteryrdquo in Fuel Cell Systems B Baker Ed Advances in Chem-istry pp 328ndash340 American Chemical Society WashingtonDC USA 1969
[37] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 485ndash510 John Wiley amp Sons New York NY USA 1968
[38] H Kim S Park J M Vohs and R J Gorte ldquoDirect oxidationof liquid fuels in a solid oxide fuel cellrdquo Journal of the Electro-chemical Society vol 148 no 7 pp A693ndashA695 2001
[39] S Islam and J M Hill ldquoBarium oxide promoted NiYSZ solid-oxide fuel cells for direct utilization of methanerdquo Journal ofMaterials Chemistry A vol 2 no 6 pp 1922ndash1929 2014
[40] C Yang J Li Y Lin J Liu F Chen and M Liu ldquoIn-situfabrication of CoFe allot nanoparticles structure (Pr
04Sr06)3
(Fe085
Nb015
)O7ceramic anode for direct hydrocarbon solid
oxde fuel cellsrdquo Nano Energy vol 11 pp 704ndash711 2015[41] S McIntosh and R J Gorte ldquoDirect hydrocarbon solid oxide
fuel cellsrdquo Chemical Reviews vol 104 no 10 pp 4845ndash48652004
[42] Y Zhao C Xia L Jia et al ldquoRecent progress on solid oxide fuelcell lowering temperature and utilizing non-hydrogen fuelsrdquoInternational Journal of Hydrogen Energy vol 38 no 36 pp16498ndash16517 2013
[43] S Srinivasan Fuel Cells From Fundamentals to ApplicationsSpringer New York NY USA 2006
[44] M RWalluk J LinMGWaller D F Smith andTA TraboldldquoDiesel auto-thermal reforming for solid oxide fuel cell systemsanode off-gas recycle simulationrdquo Applied Energy vol 130 pp94ndash102 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of Fuels 5
0010203040506070809
1
0 05 1 15 2 25 3 35 4 45
Reference
After 1st TOS experiment
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 6 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Open squaresare the Reference polarization curve Open triangles are the polar-ization curve obtained after the first time-on-stream experiment
(25 lowast SR H2On-C
16H34
= 81) In Figure 6 it is comparedto the ldquoReferencerdquo hydrogenair polarization curve fromFigure 3 The change between the Reference polarizationcurve and the one after the first time-on-stream experimentindicates that there had been a definite deterioration in thefuel cell performance The data in Figure 6 are consistentwith the deactivation observed during the TOS experimentsin Figure 4 If the two polarization curves are compared ata constant value of potential difference the current densityis much smaller after the TOS measurements than beforeEither the turnover frequency on a reaction site is muchsmaller or there are fewer reaction sites at which the reactionoccursThe only explanation is that something has preventedsmall hydrogen molecules from reacting to form electrons
Since deactivation during the TOS experiments wasobserved using both sets of operating conditions at 160∘Cfurther experiments were performed at a temperature of190∘C The MEA was treated by operating sequentially withhydrogen (6 h) water (6 h) and hydrogen (6 h) Then apolarization curve was measured The technique for mea-suring the polarization curve is indicated in Figure 7The current density was set to a constant value Thenthe potential difference was recorded until a steady-statevalue for the potential was obtained For one datum pointcorresponding to 04mAcm2 the steady-state value ofthe potential difference was extrapolated from the datain Figure 7 Generally at least one hour was requiredto obtain a steady-state value for the potential differenceFinally the steady-state values of the potential differencesobtained in Figure 7 were used in Figure 8 to constructa polarization curve for the n-hexadecanewater-air fuelcell
Some of the characteristics of the 190∘C n-hexadecaneairpolarization curve in Figure 8 are noteworthy The opencircuit potential of 05 V is much smaller than that of 093Vobtained for the hydrogenair fuel cell in Figure 3 It suggests
Figure 7 Potential difference between electrodes (V) as a functionof time (h) obtained with a PAFC Anode water flow rate =51mLh n-hexadecane flow rate = 02mLh Cathode air flowrate = 245mLmin Temperature = 190∘C pressure = 1 atm with anH2OC16H34ratio = 129 lowast SR The numbers on the top of each line
represent different current densities
0
01
02
03
04
05
06
0 005 01 015 02 025 03 035 04
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 8 Polarization curve for an n-hexadecane fueled PAFCpotential difference between the electrodes (V) and current density(mAcm2) Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
that the results in Figure 8 might represent the partialoxidation of carbon
C + 12
O2= CO 119864
0
298= 0711V (4)
as the rate limiting step in the overall reaction rather than theoxidation of n-hexadecane in (2) Equation (4) is composedof two half-cell reactions
C +H2O = CO + 2H+ + 2eminus anode (5)
2H+ + 2eminus + 12
O2= H2O cathode (6)
The difference between 0711 V and 05V might becaused by a combination of factors a temperature of 190∘Crather than 25∘C a cathode oxygen mole fraction of 021
6 Journal of Fuels
and an anode water vapour mole fraction representingequilibrium water vapour over phosphoric acid The opencircuit potential 05 V in Figure 8 is more consistent with thestandard electrochemical potential of the partial oxidationof carbon to carbon monoxide reaction 0711 V than withthe standard electrochemical potential of the oxidation ofcarbon monoxide to carbon dioxide (CO + (12)O
2=
CO2 1198640298= 133V) Initially two possible hypotheses were
suggested to explain deactivation either carbon monoxidepoisoning or deposition of carbonaceous material Equation(4) is consistent with the carbonaceous material hypothesisand not consistentwith carbonmonoxide hypothesis On thatbasis the hypothesis of deposition of carbonaceous materialseems to be the most likely explanation for the deactivationobserved during the time-on-stream experiments
Time-on-streammeasurements were also made at 190∘CThe TOS results at 190∘C are compared with those at 160∘Cin Figure 9 A steady-state operation was achieved for thelast six hours of the experiment at 190∘C A steady-stateoperation is a highly desirable result that is not alwaysachieved with a comparatively large hydrocarbon moleculesuch as hexadecane For example Okrent and Heath [36]reported unsteady cycling during which both the potentialand the current oscillated over time periods of approximately15 minutes when octane was the hydrocarbon fuel Althoughwe also observed cycling in some of our experiments thatphenomenon was not the object of our investigationThe factthat a steady-state has been demonstrated here for one set ofoperating conditions means that in principle fuel cells canoperate continuously using n-hexadecane (and presumablyother diesel type fuels)
Cleaning the MEA with water was mentioned in thediscussion pertaining to Figure 7 An example of water beingthe only reactant entering the fuel cell is shown in Figure 10The data in Figure 10 were obtained from an MEA that hadbeen used previously for 10 weeks in TOS experimentsWhenthe current density was maintained constant at a value of02mAcm2 the potential difference decreased continuouslyfor a period of 6 hours That indicated that a progressivelylarger overpotential was necessary (a larger driving force wasnecessary) tomaintain the current density at a constant valueWhen the current density was decreased to 01mAcm2 therewas an initial increase in the potential difference (smalleroverpotential) The potential difference gradually decreasedover the next 7 hours and then remained constant at 035Vfor the last 6 hours
The existence of a current densitywhenonlywaterwas fedto the fuel cell would require that some reaction must havebeen occurring Since no fuel (eg no n-hexadecane) wasfed to the fuel cell it is plausible that the reaction may haveoccurred between water and the carbonaceous material thathad been previously deposited on the MEA The existence ofa current density would also require proton migration acrossthe electrolyte The occurrence of the anode reaction shownin (5) would be consistent with both of these requirementsThe measurement of current density when only water wasfed to the fuel cell is consistent with the hypothesis thatcarbonaceous material was formed during deactivation andwas available for reaction during the water-only experiment
Figure 9 Potential differences between the electrodes (V) and time-on-stream (h) for an n-hexadecane PAFC Current density 119895 =004mAcm2 Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Pressure =1 atm
0
01
02
03
04
05
06
07
0 2 4 6 8 10 12 14 16 18 20Time-on-stream (h)
Pote
ntia
l diff
eren
ce (V
)
j = 02mAcm2j = 01mAcm2
Figure 10 Potential differences between the electrodes (V) as afunction of time-on-stream (h) when H
2O was the only feed stock
for the anode of a PAFC with a fouled MEA Anode water flowrate = 51mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
After the water-only experiments in Figure 10 werecompleted a hydrogen polarization curve was measured Itis compared with the Reference hydrogen polarization curvein Figure 11 A comparison of the results in Figure 11 (after thewater-only experiment) with the results in Figure 6 (after thefirst TOS experiment) indicates that a substantial improve-ment was caused by the water-only treatment That suggeststhe water-only experiment cleaned the MEA Cleaning of theMEA would be consistent with removal of a carbonaceousdeposit from the catalyst surface
The results reported here can be comparedwith other fuelcell systems Two of the important criteria are capital costand energy efficiency The capital cost is strongly influencedby the size of the fuel cell stack that in turn is a function ofcurrent density The theoretical energy efficiency is relatedto the thermodynamic efficiency of the reactions that occur
Journal of Fuels 7
0010203040506070809
1
0 05 1 15 2 25 3 35 4
After water-onlyexperiments
Reference
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 11 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Solid circles aredata obtained after a one-week experiment with water-only (on anMEA that had been used in TOS experiments for ten weeks) Opensquares are data for the Reference polarization curve
The reaction networks that occur vary with the particulartype of fuel cell systemThe operating cost of a fuel cell systemis strongly influenced by the energy efficiency
Small current densities were obtained for the low-temperature (190∘C) direct hydrocarbon (n-hexadecane)PAFC results without a reforming unit reported here Thereare extensive reviews describing results obtained by PAFCsoperating on hydrocarbons without a reforming unit [2ndash4]In general the current densities are quite small Thereforelarge reactors having a large capital cost would be requiredIn contrast Kim et al [38] reported much larger currentdensities using a higher temperature (700∘C) solid oxide fuelcell SOFC without a reforming unit when it was operatingon synthetic diesel fuel Interest in these systems specificallythe development of anodes continues to be an active area ofresearch [39 40] There have been several reviews of directhydrocarbon SOFCs without reforming units [13 41 42]Although no reforming unit was used they indicate thatinternal reforming occurs [13] Unfortunately the reformingreaction (internal or external) has a negative effect onenergy efficiency Approximately 25 of the hydrocarbonfuel must be used to provide the endothermic heat ofreaction for the reforming reaction At the low temperaturesused in this study the reforming reaction is thermodynam-ically unfavourable and does not occur Therefore the high-temperature SOFC systems will have a capital cost advantageover the lower temperature PAFC systemused here Howeverthe lower temperature PAFC system used here will havea theoretical energy efficiency advantage over the SOFCsystem
The use of an external reformer in combination with aPAFC system is a well-established technology that convertsthe hydrocarbon to hydrogen in a fuel processing system andthen uses the hydrogen as the fuel in a fuel cell system Bythe year 2006 more than 200 commercial plants had beensold [43] Nevertheless research on improving the reforming
process continues [44]The reforming reaction in an externalreformer has the same negative effect on energy efficiencythat was mentioned above for internal reforming The fuelprocessing system includes four processes steam reforminghigh-temperature water shift low-temperature shift andhydrogen purification Equipment for those four processeshas a substantial capital cost In contrast there is no capitalcost for a reformerfuel processor with the low-temperaturedirect hydrocarbon PAFC system described here
4 Conclusions
This study reported the first polarization curve evermeasuredforwhich n-hexadecanewas the fuel at the anode of a fuel cellThe current densities were found to be very small
Deactivation was observed in time-on-stream experi-ments Deactivation as measured by the change in potentialdifference was found to be a linear function of the cumulativecharge transferred across the electrolyte of the fuel cellDeactivation during fuel cell experiments with n-hexadecanewas confirmed by comparing hydrogen polarization curvesbefore and after the time-on-stream measurements For agiven potential difference the current densities were muchsmaller for the hydrogen polarization curves measured afterthe time-on-stream experiments
Experiments were performed in whichwater was the onlyreactant entering the fuel cell that had been used previouslyfor 10 weeks in time-on-stream experiments Current den-sities were measured during those experiments indicatingthat the water must have reacted with some type of speciesthat remained on the fuel cell catalyst at the end of thetime-on-stream experiments When a hydrogen polarizationcurvewasmeasured at the end of thewater-only experimentsit was close to that measured before the time-on-streamexperiments That indicates that the deactivating species onthe surface of the platinum particles had been removed andthat it was possible to regenerate deactivated MEAs
A hypothesis that carbonaceous material was depositedon the platinum anode catalyst particles was suggested toexplain the deactivation Four types of observations wereconsistent with that hypothesis (a) the change in potentialdifference during time-on-stream measurements (b) whenhydrogen polarization curves measured before and after thetime-on-stream experiments were compared the currentdensities measured after TOS were much smaller than thosemeasured before TOS (c) current densities were measuredwhen water was the only reactant entering the fuel cell Inorder to produce a current density water must have reactedwith some type of species that had been deposited on thesurface of the platinum particles and (d) the open circuitpotential of a n-hexadecane fuel cell 05 V was much closerto the standard electrochemical potential for the carbon-water reaction 0711 V than to that for the carbonmonoxide-water reaction 133 V Observation (d) makes a hypothesisof deactivation by carbonaceous materials more likely thandeactivation by carbon monoxide poisoning
Steady-state operation of the n-hexadecane fuel cellwithout additional deactivation was observed at one set of
8 Journal of Fuels
fuel cell operating conditionsThat observation demonstratesthat stable fuel cell operation is technically feasible whenn-hexadecane is the fuel at the anode of a fuel cell Itsuggests there ismerit in investigating fuel cell operationwithcommercial fuels such as petroleum diesel or biodiesel
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this research anddevelopment project was supported by a grant from Trans-port Canadarsquos Clean Rail Academic Grant Program and bya Discovery Grant from the Canadian Governmentrsquos NaturalSciences and Engineering Research Council
References
[1] J A A Ketelaar ldquoHistoryrdquo in Fuel Cell Systems L JM J Blomenand M N Mugerwa Eds p 20 Plenum Press New York NYUSA 1993
[2] E J Cairns ldquoAnodic oxidation of hydrocarbons and thehydrocarbon fuel cellrdquoAdvances in Electrochemistry Science andElectrochemical Engineering vol 8 pp 337ndash392 1971
[3] J O M Bockris and S Srinivasan ldquoElectrochemical combus-tion of organic substancesrdquo in Fuel CellsTheir Electrochemistrypp 357ndash411 McGraw-Hill New York NY USA 1969
[4] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 458ndash523 John Wiley amp Sons New York NY USA 1968
[5] S Bertholet Oxydation Electrocatalytique du Methane [PhDDissertation] Universite de Poitiers Poitiers France 1998
[6] C K Cheng J L Luo K T Chuang and A R SangerldquoPropane fuel cells using phosphoric-acid-doped polybenzim-idazole membranesrdquo The Journal of Physical Chemistry B vol109 no 26 pp 13036ndash13042 2005
[7] O Savadogo and F J Rodriguez Varela ldquoLow-temperaturedirect propane polymer electrolyte membranes fuel cellrdquo Jour-nal of New Materials for Electrochemical Systems vol 4 no 2pp 93ndash97 2001
[8] F J Rodrıguez Varela and O Savadogo ldquoReal-time massspectrometric analysis of the anode exhaust gases of a directpropane fuel cellrdquo Journal of the Electrochemical Society vol 152no 9 pp A1755ndashA1762 2005
[9] P Heo K Ito A Tomita and T Hibino ldquoA proton-conductingfuel cell operating with hydrocarbon fuelsrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7841ndash78442008
[10] B C H Steele I Kelly H Middleton and R Rudkin ldquoOxida-tion of methane in solid state electrochemical reactorsrdquo SolidState Ionics vol 28ndash30 no 2 pp 1547ndash1552 1988
[11] E P Murray T Tsai and S A Barnett ldquoA direct-methane fuelcell with a ceria-based anoderdquo Nature vol 400 no 6745 pp649ndash651 1999
[12] W Zhu C Xia J Fan R Peng and G Meng ldquoCeria coated Nias anodes for direct utilization of methane in low-temperature
solid oxide fuel cellsrdquo Journal of Power Sources vol 160 no 2pp 897ndash902 2006
[13] M D Gross J M Vohs and R J Gorte ldquoRecent progress inSOFC anodes for direct utilization of hydrocarbonsrdquo Journal ofMaterials Chemistry vol 17 no 30 pp 3071ndash3077 2007
[14] J G Lee C M Lee M Park and Y G Shul ldquoDirect methanefuel cell with La
2Sn2O7ndashNindashGd
01Ce09O195
anode and electro-spun La
06Sr04Co02Fe08O3minus120575
ndashGd01Ce09O195
cathoderdquo RoyalSociety of Chemistry Advances vol 3 no 29 pp 11816ndash118222013
[15] D Ding Z Liu L Li andC Xia ldquoAn octane-fueled low temper-ature solid oxide fuel cell with Ru-free anodesrdquo ElectrochemistryCommunications vol 10 no 9 pp 1295ndash1298 2008
[16] H Kishimoto K Yamaji T Horita et al ldquoFeasibility of liquidhydrocarbon fuels for SOFC with Ni-ScSZ anoderdquo Journal ofPower Sources vol 172 no 1 pp 67ndash71 2007
[17] Z F Zhou C Gallo M B Pague H Schobert and S N LvovldquoDirect oxidation of jet fuels and Pennsylvania crude oil in asolid oxide fuel cellrdquo Journal of Power Sources vol 133 no 2 pp181ndash187 2004
[18] G Psofogiannakis Y Bourgault B E Conway and M TernanldquoMathematical model for a direct propane phosphoric acid fuelcellrdquo Journal of Applied Electrochemistry vol 36 no 1 pp 115ndash130 2006
[19] H Khakdaman Y Bourgault and M Ternan ldquoComputationalmodeling of a direct propane fuel cellrdquo Journal of Power Sourcesvol 196 no 6 pp 3186ndash3194 2011
[20] H R Khakdaman Y Bourgault and M Ternan ldquoDirectpropane fuel cell anode with interdigitated flow fields two-dimensional modelrdquo Industrial amp Engineering ChemistryResearch vol 49 no 3 pp 1079ndash1085 2010
[21] G Psofogiannakis A St-Amant andM Ternan ldquoAb-initioDFTstudy of methane electro-oxidation mechanism on platinumrdquoJournal of Physical Chemistry B vol 110 pp 24593ndash24605 2006
[22] S Vafaeyan A St-Amant andM Ternan ldquoNickel alloy catalystsfor the anode of a high temperature PEM direct propane fuelcellrdquo Journal of Chemistry vol 2014 Article ID 151638 8 pages2014
[23] S Vafaeyan A St-Amant and M Ternan ldquoPropane fuel cellsselectivity for partial or complete reactionrdquo Journal of Fuels vol2014 Article ID 485045 9 pages 2014
[24] A Al-Othman A Y Tremblay W Pell et al ldquoA modified silicicacid (Si) and sulphuric acid (S)-ZrPPTFEglycerol compositemembrane for high temperature direct hydrocarbon fuel cellsrdquoJournal of Power Sources vol 224 pp 158ndash167 2013
[25] A Al-Othman A Y Tremblay W Pell Y Liu B A Peppleyand M Ternan ldquoThe effect of glycerol on the conductivity ofNafion-free ZrPPTFE composite membrane electrolytes fordirect hydrocarbon fuel cellsrdquo Journal of Power Sources vol 199pp 14ndash21 2012
[26] A Al-Othman A Y Tremblay W Pell et al ldquoZirconium phos-phate as the proton conducting material in direct hydrocarbonpolymer electrolyte membrane fuel cells operating above theboiling point of waterrdquo Journal of Power Sources vol 195 no9 pp 2520ndash2525 2010
[27] C G Farrell C L Gardner and M Ternan ldquoExperimental andmodelling studies of CO poisoning in PEM fuel cellsrdquo Journalof Power Sources vol 171 no 2 pp 282ndash293 2007
[28] R Fonocho C L Gardner and M Ternan ldquoA study of theelectrochemical hydrogenation of o-xylene in a PEM hydro-genation reactorrdquo Electrochimica Acta vol 75 pp 171ndash178 2012
Journal of Fuels 9
[29] N Sammes R Bove and K Stahl ldquoPhosphoric acid fuel cellsfundamentals and applicationsrdquo Current Opinion in Solid Stateand Materials Science vol 8 no 5 pp 372ndash378 2004
[30] J M King and H R Kunz ldquoPhosphoric acid electrolyte fuelcellsrdquo in Handbook of Fuel Cells W Vielstich A Lamm HA Gasteiger and H Yokokawa Eds vol 1 pp 287ndash300 JohnWiley amp Sons New York NY USA 2010
[31] S R Choudhury ldquoPhosphoric acid fuel cell technologyrdquo inRecent Trends in Fuel Cell Science and Technology S Basu Edpp 188ndash216 Springer New York NY USA 2007
[32] W Grubb and C J Michalske ldquoA high performance propanefuel cell operating in the temperature range of 150∘ndash200∘CrdquoJournal of The Electrochemical Society vol 111 no 9 p 10151964
[33] H A Liebhafsky andW T Grubb ldquoNormal alkanes at platinumanodesrdquo Fuel Preprints vol 11 no 2 p 134 1967
[34] V S Bagotzky Y B Vassiliev and O A Khazova ldquoGeneralizedscheme of chemisorption electrooxidation and electroreduc-tion of simple organic compounds on platinum group metalsrdquoJournal of Electroanalytical Chemistry and Interfacial Electro-chemistry vol 81 no 2 pp 229ndash238 1977
[35] T F Fuller F J Luczak and D J Wheeler ldquoElectrocatalystutilization in phosphoric acid fuel cellsrdquo Journal of the Electro-chemical Society vol 142 no 6 pp 1752ndash1757 1995
[36] E H Okrent and C E Heath ldquoA liquid hydrocarbon fuel cellbatteryrdquo in Fuel Cell Systems B Baker Ed Advances in Chem-istry pp 328ndash340 American Chemical Society WashingtonDC USA 1969
[37] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 485ndash510 John Wiley amp Sons New York NY USA 1968
[38] H Kim S Park J M Vohs and R J Gorte ldquoDirect oxidationof liquid fuels in a solid oxide fuel cellrdquo Journal of the Electro-chemical Society vol 148 no 7 pp A693ndashA695 2001
[39] S Islam and J M Hill ldquoBarium oxide promoted NiYSZ solid-oxide fuel cells for direct utilization of methanerdquo Journal ofMaterials Chemistry A vol 2 no 6 pp 1922ndash1929 2014
[40] C Yang J Li Y Lin J Liu F Chen and M Liu ldquoIn-situfabrication of CoFe allot nanoparticles structure (Pr
04Sr06)3
(Fe085
Nb015
)O7ceramic anode for direct hydrocarbon solid
oxde fuel cellsrdquo Nano Energy vol 11 pp 704ndash711 2015[41] S McIntosh and R J Gorte ldquoDirect hydrocarbon solid oxide
fuel cellsrdquo Chemical Reviews vol 104 no 10 pp 4845ndash48652004
[42] Y Zhao C Xia L Jia et al ldquoRecent progress on solid oxide fuelcell lowering temperature and utilizing non-hydrogen fuelsrdquoInternational Journal of Hydrogen Energy vol 38 no 36 pp16498ndash16517 2013
[43] S Srinivasan Fuel Cells From Fundamentals to ApplicationsSpringer New York NY USA 2006
[44] M RWalluk J LinMGWaller D F Smith andTA TraboldldquoDiesel auto-thermal reforming for solid oxide fuel cell systemsanode off-gas recycle simulationrdquo Applied Energy vol 130 pp94ndash102 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
6 Journal of Fuels
and an anode water vapour mole fraction representingequilibrium water vapour over phosphoric acid The opencircuit potential 05 V in Figure 8 is more consistent with thestandard electrochemical potential of the partial oxidationof carbon to carbon monoxide reaction 0711 V than withthe standard electrochemical potential of the oxidation ofcarbon monoxide to carbon dioxide (CO + (12)O
2=
CO2 1198640298= 133V) Initially two possible hypotheses were
suggested to explain deactivation either carbon monoxidepoisoning or deposition of carbonaceous material Equation(4) is consistent with the carbonaceous material hypothesisand not consistentwith carbonmonoxide hypothesis On thatbasis the hypothesis of deposition of carbonaceous materialseems to be the most likely explanation for the deactivationobserved during the time-on-stream experiments
Time-on-streammeasurements were also made at 190∘CThe TOS results at 190∘C are compared with those at 160∘Cin Figure 9 A steady-state operation was achieved for thelast six hours of the experiment at 190∘C A steady-stateoperation is a highly desirable result that is not alwaysachieved with a comparatively large hydrocarbon moleculesuch as hexadecane For example Okrent and Heath [36]reported unsteady cycling during which both the potentialand the current oscillated over time periods of approximately15 minutes when octane was the hydrocarbon fuel Althoughwe also observed cycling in some of our experiments thatphenomenon was not the object of our investigationThe factthat a steady-state has been demonstrated here for one set ofoperating conditions means that in principle fuel cells canoperate continuously using n-hexadecane (and presumablyother diesel type fuels)
Cleaning the MEA with water was mentioned in thediscussion pertaining to Figure 7 An example of water beingthe only reactant entering the fuel cell is shown in Figure 10The data in Figure 10 were obtained from an MEA that hadbeen used previously for 10 weeks in TOS experimentsWhenthe current density was maintained constant at a value of02mAcm2 the potential difference decreased continuouslyfor a period of 6 hours That indicated that a progressivelylarger overpotential was necessary (a larger driving force wasnecessary) tomaintain the current density at a constant valueWhen the current density was decreased to 01mAcm2 therewas an initial increase in the potential difference (smalleroverpotential) The potential difference gradually decreasedover the next 7 hours and then remained constant at 035Vfor the last 6 hours
The existence of a current densitywhenonlywaterwas fedto the fuel cell would require that some reaction must havebeen occurring Since no fuel (eg no n-hexadecane) wasfed to the fuel cell it is plausible that the reaction may haveoccurred between water and the carbonaceous material thathad been previously deposited on the MEA The existence ofa current density would also require proton migration acrossthe electrolyte The occurrence of the anode reaction shownin (5) would be consistent with both of these requirementsThe measurement of current density when only water wasfed to the fuel cell is consistent with the hypothesis thatcarbonaceous material was formed during deactivation andwas available for reaction during the water-only experiment
Figure 9 Potential differences between the electrodes (V) and time-on-stream (h) for an n-hexadecane PAFC Current density 119895 =004mAcm2 Anode water flow rate = 51mLh n-hexadecane flowrate = 02mLh Cathode air flow rate = 245mLmin Pressure =1 atm
0
01
02
03
04
05
06
07
0 2 4 6 8 10 12 14 16 18 20Time-on-stream (h)
Pote
ntia
l diff
eren
ce (V
)
j = 02mAcm2j = 01mAcm2
Figure 10 Potential differences between the electrodes (V) as afunction of time-on-stream (h) when H
2O was the only feed stock
for the anode of a PAFC with a fouled MEA Anode water flowrate = 51mLh Cathode air flow rate = 245mLmin Temperature =190∘C Pressure = 1 atm
After the water-only experiments in Figure 10 werecompleted a hydrogen polarization curve was measured Itis compared with the Reference hydrogen polarization curvein Figure 11 A comparison of the results in Figure 11 (after thewater-only experiment) with the results in Figure 6 (after thefirst TOS experiment) indicates that a substantial improve-ment was caused by the water-only treatment That suggeststhe water-only experiment cleaned the MEA Cleaning of theMEA would be consistent with removal of a carbonaceousdeposit from the catalyst surface
The results reported here can be comparedwith other fuelcell systems Two of the important criteria are capital costand energy efficiency The capital cost is strongly influencedby the size of the fuel cell stack that in turn is a function ofcurrent density The theoretical energy efficiency is relatedto the thermodynamic efficiency of the reactions that occur
Journal of Fuels 7
0010203040506070809
1
0 05 1 15 2 25 3 35 4
After water-onlyexperiments
Reference
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 11 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Solid circles aredata obtained after a one-week experiment with water-only (on anMEA that had been used in TOS experiments for ten weeks) Opensquares are data for the Reference polarization curve
The reaction networks that occur vary with the particulartype of fuel cell systemThe operating cost of a fuel cell systemis strongly influenced by the energy efficiency
Small current densities were obtained for the low-temperature (190∘C) direct hydrocarbon (n-hexadecane)PAFC results without a reforming unit reported here Thereare extensive reviews describing results obtained by PAFCsoperating on hydrocarbons without a reforming unit [2ndash4]In general the current densities are quite small Thereforelarge reactors having a large capital cost would be requiredIn contrast Kim et al [38] reported much larger currentdensities using a higher temperature (700∘C) solid oxide fuelcell SOFC without a reforming unit when it was operatingon synthetic diesel fuel Interest in these systems specificallythe development of anodes continues to be an active area ofresearch [39 40] There have been several reviews of directhydrocarbon SOFCs without reforming units [13 41 42]Although no reforming unit was used they indicate thatinternal reforming occurs [13] Unfortunately the reformingreaction (internal or external) has a negative effect onenergy efficiency Approximately 25 of the hydrocarbonfuel must be used to provide the endothermic heat ofreaction for the reforming reaction At the low temperaturesused in this study the reforming reaction is thermodynam-ically unfavourable and does not occur Therefore the high-temperature SOFC systems will have a capital cost advantageover the lower temperature PAFC systemused here Howeverthe lower temperature PAFC system used here will havea theoretical energy efficiency advantage over the SOFCsystem
The use of an external reformer in combination with aPAFC system is a well-established technology that convertsthe hydrocarbon to hydrogen in a fuel processing system andthen uses the hydrogen as the fuel in a fuel cell system Bythe year 2006 more than 200 commercial plants had beensold [43] Nevertheless research on improving the reforming
process continues [44]The reforming reaction in an externalreformer has the same negative effect on energy efficiencythat was mentioned above for internal reforming The fuelprocessing system includes four processes steam reforminghigh-temperature water shift low-temperature shift andhydrogen purification Equipment for those four processeshas a substantial capital cost In contrast there is no capitalcost for a reformerfuel processor with the low-temperaturedirect hydrocarbon PAFC system described here
4 Conclusions
This study reported the first polarization curve evermeasuredforwhich n-hexadecanewas the fuel at the anode of a fuel cellThe current densities were found to be very small
Deactivation was observed in time-on-stream experi-ments Deactivation as measured by the change in potentialdifference was found to be a linear function of the cumulativecharge transferred across the electrolyte of the fuel cellDeactivation during fuel cell experiments with n-hexadecanewas confirmed by comparing hydrogen polarization curvesbefore and after the time-on-stream measurements For agiven potential difference the current densities were muchsmaller for the hydrogen polarization curves measured afterthe time-on-stream experiments
Experiments were performed in whichwater was the onlyreactant entering the fuel cell that had been used previouslyfor 10 weeks in time-on-stream experiments Current den-sities were measured during those experiments indicatingthat the water must have reacted with some type of speciesthat remained on the fuel cell catalyst at the end of thetime-on-stream experiments When a hydrogen polarizationcurvewasmeasured at the end of thewater-only experimentsit was close to that measured before the time-on-streamexperiments That indicates that the deactivating species onthe surface of the platinum particles had been removed andthat it was possible to regenerate deactivated MEAs
A hypothesis that carbonaceous material was depositedon the platinum anode catalyst particles was suggested toexplain the deactivation Four types of observations wereconsistent with that hypothesis (a) the change in potentialdifference during time-on-stream measurements (b) whenhydrogen polarization curves measured before and after thetime-on-stream experiments were compared the currentdensities measured after TOS were much smaller than thosemeasured before TOS (c) current densities were measuredwhen water was the only reactant entering the fuel cell Inorder to produce a current density water must have reactedwith some type of species that had been deposited on thesurface of the platinum particles and (d) the open circuitpotential of a n-hexadecane fuel cell 05 V was much closerto the standard electrochemical potential for the carbon-water reaction 0711 V than to that for the carbonmonoxide-water reaction 133 V Observation (d) makes a hypothesisof deactivation by carbonaceous materials more likely thandeactivation by carbon monoxide poisoning
Steady-state operation of the n-hexadecane fuel cellwithout additional deactivation was observed at one set of
8 Journal of Fuels
fuel cell operating conditionsThat observation demonstratesthat stable fuel cell operation is technically feasible whenn-hexadecane is the fuel at the anode of a fuel cell Itsuggests there ismerit in investigating fuel cell operationwithcommercial fuels such as petroleum diesel or biodiesel
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this research anddevelopment project was supported by a grant from Trans-port Canadarsquos Clean Rail Academic Grant Program and bya Discovery Grant from the Canadian Governmentrsquos NaturalSciences and Engineering Research Council
References
[1] J A A Ketelaar ldquoHistoryrdquo in Fuel Cell Systems L JM J Blomenand M N Mugerwa Eds p 20 Plenum Press New York NYUSA 1993
[2] E J Cairns ldquoAnodic oxidation of hydrocarbons and thehydrocarbon fuel cellrdquoAdvances in Electrochemistry Science andElectrochemical Engineering vol 8 pp 337ndash392 1971
[3] J O M Bockris and S Srinivasan ldquoElectrochemical combus-tion of organic substancesrdquo in Fuel CellsTheir Electrochemistrypp 357ndash411 McGraw-Hill New York NY USA 1969
[4] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 458ndash523 John Wiley amp Sons New York NY USA 1968
[5] S Bertholet Oxydation Electrocatalytique du Methane [PhDDissertation] Universite de Poitiers Poitiers France 1998
[6] C K Cheng J L Luo K T Chuang and A R SangerldquoPropane fuel cells using phosphoric-acid-doped polybenzim-idazole membranesrdquo The Journal of Physical Chemistry B vol109 no 26 pp 13036ndash13042 2005
[7] O Savadogo and F J Rodriguez Varela ldquoLow-temperaturedirect propane polymer electrolyte membranes fuel cellrdquo Jour-nal of New Materials for Electrochemical Systems vol 4 no 2pp 93ndash97 2001
[8] F J Rodrıguez Varela and O Savadogo ldquoReal-time massspectrometric analysis of the anode exhaust gases of a directpropane fuel cellrdquo Journal of the Electrochemical Society vol 152no 9 pp A1755ndashA1762 2005
[9] P Heo K Ito A Tomita and T Hibino ldquoA proton-conductingfuel cell operating with hydrocarbon fuelsrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7841ndash78442008
[10] B C H Steele I Kelly H Middleton and R Rudkin ldquoOxida-tion of methane in solid state electrochemical reactorsrdquo SolidState Ionics vol 28ndash30 no 2 pp 1547ndash1552 1988
[11] E P Murray T Tsai and S A Barnett ldquoA direct-methane fuelcell with a ceria-based anoderdquo Nature vol 400 no 6745 pp649ndash651 1999
[12] W Zhu C Xia J Fan R Peng and G Meng ldquoCeria coated Nias anodes for direct utilization of methane in low-temperature
solid oxide fuel cellsrdquo Journal of Power Sources vol 160 no 2pp 897ndash902 2006
[13] M D Gross J M Vohs and R J Gorte ldquoRecent progress inSOFC anodes for direct utilization of hydrocarbonsrdquo Journal ofMaterials Chemistry vol 17 no 30 pp 3071ndash3077 2007
[14] J G Lee C M Lee M Park and Y G Shul ldquoDirect methanefuel cell with La
2Sn2O7ndashNindashGd
01Ce09O195
anode and electro-spun La
06Sr04Co02Fe08O3minus120575
ndashGd01Ce09O195
cathoderdquo RoyalSociety of Chemistry Advances vol 3 no 29 pp 11816ndash118222013
[15] D Ding Z Liu L Li andC Xia ldquoAn octane-fueled low temper-ature solid oxide fuel cell with Ru-free anodesrdquo ElectrochemistryCommunications vol 10 no 9 pp 1295ndash1298 2008
[16] H Kishimoto K Yamaji T Horita et al ldquoFeasibility of liquidhydrocarbon fuels for SOFC with Ni-ScSZ anoderdquo Journal ofPower Sources vol 172 no 1 pp 67ndash71 2007
[17] Z F Zhou C Gallo M B Pague H Schobert and S N LvovldquoDirect oxidation of jet fuels and Pennsylvania crude oil in asolid oxide fuel cellrdquo Journal of Power Sources vol 133 no 2 pp181ndash187 2004
[18] G Psofogiannakis Y Bourgault B E Conway and M TernanldquoMathematical model for a direct propane phosphoric acid fuelcellrdquo Journal of Applied Electrochemistry vol 36 no 1 pp 115ndash130 2006
[19] H Khakdaman Y Bourgault and M Ternan ldquoComputationalmodeling of a direct propane fuel cellrdquo Journal of Power Sourcesvol 196 no 6 pp 3186ndash3194 2011
[20] H R Khakdaman Y Bourgault and M Ternan ldquoDirectpropane fuel cell anode with interdigitated flow fields two-dimensional modelrdquo Industrial amp Engineering ChemistryResearch vol 49 no 3 pp 1079ndash1085 2010
[21] G Psofogiannakis A St-Amant andM Ternan ldquoAb-initioDFTstudy of methane electro-oxidation mechanism on platinumrdquoJournal of Physical Chemistry B vol 110 pp 24593ndash24605 2006
[22] S Vafaeyan A St-Amant andM Ternan ldquoNickel alloy catalystsfor the anode of a high temperature PEM direct propane fuelcellrdquo Journal of Chemistry vol 2014 Article ID 151638 8 pages2014
[23] S Vafaeyan A St-Amant and M Ternan ldquoPropane fuel cellsselectivity for partial or complete reactionrdquo Journal of Fuels vol2014 Article ID 485045 9 pages 2014
[24] A Al-Othman A Y Tremblay W Pell et al ldquoA modified silicicacid (Si) and sulphuric acid (S)-ZrPPTFEglycerol compositemembrane for high temperature direct hydrocarbon fuel cellsrdquoJournal of Power Sources vol 224 pp 158ndash167 2013
[25] A Al-Othman A Y Tremblay W Pell Y Liu B A Peppleyand M Ternan ldquoThe effect of glycerol on the conductivity ofNafion-free ZrPPTFE composite membrane electrolytes fordirect hydrocarbon fuel cellsrdquo Journal of Power Sources vol 199pp 14ndash21 2012
[26] A Al-Othman A Y Tremblay W Pell et al ldquoZirconium phos-phate as the proton conducting material in direct hydrocarbonpolymer electrolyte membrane fuel cells operating above theboiling point of waterrdquo Journal of Power Sources vol 195 no9 pp 2520ndash2525 2010
[27] C G Farrell C L Gardner and M Ternan ldquoExperimental andmodelling studies of CO poisoning in PEM fuel cellsrdquo Journalof Power Sources vol 171 no 2 pp 282ndash293 2007
[28] R Fonocho C L Gardner and M Ternan ldquoA study of theelectrochemical hydrogenation of o-xylene in a PEM hydro-genation reactorrdquo Electrochimica Acta vol 75 pp 171ndash178 2012
Journal of Fuels 9
[29] N Sammes R Bove and K Stahl ldquoPhosphoric acid fuel cellsfundamentals and applicationsrdquo Current Opinion in Solid Stateand Materials Science vol 8 no 5 pp 372ndash378 2004
[30] J M King and H R Kunz ldquoPhosphoric acid electrolyte fuelcellsrdquo in Handbook of Fuel Cells W Vielstich A Lamm HA Gasteiger and H Yokokawa Eds vol 1 pp 287ndash300 JohnWiley amp Sons New York NY USA 2010
[31] S R Choudhury ldquoPhosphoric acid fuel cell technologyrdquo inRecent Trends in Fuel Cell Science and Technology S Basu Edpp 188ndash216 Springer New York NY USA 2007
[32] W Grubb and C J Michalske ldquoA high performance propanefuel cell operating in the temperature range of 150∘ndash200∘CrdquoJournal of The Electrochemical Society vol 111 no 9 p 10151964
[33] H A Liebhafsky andW T Grubb ldquoNormal alkanes at platinumanodesrdquo Fuel Preprints vol 11 no 2 p 134 1967
[34] V S Bagotzky Y B Vassiliev and O A Khazova ldquoGeneralizedscheme of chemisorption electrooxidation and electroreduc-tion of simple organic compounds on platinum group metalsrdquoJournal of Electroanalytical Chemistry and Interfacial Electro-chemistry vol 81 no 2 pp 229ndash238 1977
[35] T F Fuller F J Luczak and D J Wheeler ldquoElectrocatalystutilization in phosphoric acid fuel cellsrdquo Journal of the Electro-chemical Society vol 142 no 6 pp 1752ndash1757 1995
[36] E H Okrent and C E Heath ldquoA liquid hydrocarbon fuel cellbatteryrdquo in Fuel Cell Systems B Baker Ed Advances in Chem-istry pp 328ndash340 American Chemical Society WashingtonDC USA 1969
[37] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 485ndash510 John Wiley amp Sons New York NY USA 1968
[38] H Kim S Park J M Vohs and R J Gorte ldquoDirect oxidationof liquid fuels in a solid oxide fuel cellrdquo Journal of the Electro-chemical Society vol 148 no 7 pp A693ndashA695 2001
[39] S Islam and J M Hill ldquoBarium oxide promoted NiYSZ solid-oxide fuel cells for direct utilization of methanerdquo Journal ofMaterials Chemistry A vol 2 no 6 pp 1922ndash1929 2014
[40] C Yang J Li Y Lin J Liu F Chen and M Liu ldquoIn-situfabrication of CoFe allot nanoparticles structure (Pr
04Sr06)3
(Fe085
Nb015
)O7ceramic anode for direct hydrocarbon solid
oxde fuel cellsrdquo Nano Energy vol 11 pp 704ndash711 2015[41] S McIntosh and R J Gorte ldquoDirect hydrocarbon solid oxide
fuel cellsrdquo Chemical Reviews vol 104 no 10 pp 4845ndash48652004
[42] Y Zhao C Xia L Jia et al ldquoRecent progress on solid oxide fuelcell lowering temperature and utilizing non-hydrogen fuelsrdquoInternational Journal of Hydrogen Energy vol 38 no 36 pp16498ndash16517 2013
[43] S Srinivasan Fuel Cells From Fundamentals to ApplicationsSpringer New York NY USA 2006
[44] M RWalluk J LinMGWaller D F Smith andTA TraboldldquoDiesel auto-thermal reforming for solid oxide fuel cell systemsanode off-gas recycle simulationrdquo Applied Energy vol 130 pp94ndash102 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of Fuels 7
0010203040506070809
1
0 05 1 15 2 25 3 35 4
After water-onlyexperiments
Reference
Pote
ntia
l diff
eren
ce (V
)
Current density (mAcm2)
Figure 11 Polarization curve for a hydrogen fueled PAFC potentialdifference between the electrodes and current density (mAcm2)Anode hydrogen flow rate = 96mLmin Cathode air flow rate =245mLmin Temperature = 160∘C Pressure = 1 atm Solid circles aredata obtained after a one-week experiment with water-only (on anMEA that had been used in TOS experiments for ten weeks) Opensquares are data for the Reference polarization curve
The reaction networks that occur vary with the particulartype of fuel cell systemThe operating cost of a fuel cell systemis strongly influenced by the energy efficiency
Small current densities were obtained for the low-temperature (190∘C) direct hydrocarbon (n-hexadecane)PAFC results without a reforming unit reported here Thereare extensive reviews describing results obtained by PAFCsoperating on hydrocarbons without a reforming unit [2ndash4]In general the current densities are quite small Thereforelarge reactors having a large capital cost would be requiredIn contrast Kim et al [38] reported much larger currentdensities using a higher temperature (700∘C) solid oxide fuelcell SOFC without a reforming unit when it was operatingon synthetic diesel fuel Interest in these systems specificallythe development of anodes continues to be an active area ofresearch [39 40] There have been several reviews of directhydrocarbon SOFCs without reforming units [13 41 42]Although no reforming unit was used they indicate thatinternal reforming occurs [13] Unfortunately the reformingreaction (internal or external) has a negative effect onenergy efficiency Approximately 25 of the hydrocarbonfuel must be used to provide the endothermic heat ofreaction for the reforming reaction At the low temperaturesused in this study the reforming reaction is thermodynam-ically unfavourable and does not occur Therefore the high-temperature SOFC systems will have a capital cost advantageover the lower temperature PAFC systemused here Howeverthe lower temperature PAFC system used here will havea theoretical energy efficiency advantage over the SOFCsystem
The use of an external reformer in combination with aPAFC system is a well-established technology that convertsthe hydrocarbon to hydrogen in a fuel processing system andthen uses the hydrogen as the fuel in a fuel cell system Bythe year 2006 more than 200 commercial plants had beensold [43] Nevertheless research on improving the reforming
process continues [44]The reforming reaction in an externalreformer has the same negative effect on energy efficiencythat was mentioned above for internal reforming The fuelprocessing system includes four processes steam reforminghigh-temperature water shift low-temperature shift andhydrogen purification Equipment for those four processeshas a substantial capital cost In contrast there is no capitalcost for a reformerfuel processor with the low-temperaturedirect hydrocarbon PAFC system described here
4 Conclusions
This study reported the first polarization curve evermeasuredforwhich n-hexadecanewas the fuel at the anode of a fuel cellThe current densities were found to be very small
Deactivation was observed in time-on-stream experi-ments Deactivation as measured by the change in potentialdifference was found to be a linear function of the cumulativecharge transferred across the electrolyte of the fuel cellDeactivation during fuel cell experiments with n-hexadecanewas confirmed by comparing hydrogen polarization curvesbefore and after the time-on-stream measurements For agiven potential difference the current densities were muchsmaller for the hydrogen polarization curves measured afterthe time-on-stream experiments
Experiments were performed in whichwater was the onlyreactant entering the fuel cell that had been used previouslyfor 10 weeks in time-on-stream experiments Current den-sities were measured during those experiments indicatingthat the water must have reacted with some type of speciesthat remained on the fuel cell catalyst at the end of thetime-on-stream experiments When a hydrogen polarizationcurvewasmeasured at the end of thewater-only experimentsit was close to that measured before the time-on-streamexperiments That indicates that the deactivating species onthe surface of the platinum particles had been removed andthat it was possible to regenerate deactivated MEAs
A hypothesis that carbonaceous material was depositedon the platinum anode catalyst particles was suggested toexplain the deactivation Four types of observations wereconsistent with that hypothesis (a) the change in potentialdifference during time-on-stream measurements (b) whenhydrogen polarization curves measured before and after thetime-on-stream experiments were compared the currentdensities measured after TOS were much smaller than thosemeasured before TOS (c) current densities were measuredwhen water was the only reactant entering the fuel cell Inorder to produce a current density water must have reactedwith some type of species that had been deposited on thesurface of the platinum particles and (d) the open circuitpotential of a n-hexadecane fuel cell 05 V was much closerto the standard electrochemical potential for the carbon-water reaction 0711 V than to that for the carbonmonoxide-water reaction 133 V Observation (d) makes a hypothesisof deactivation by carbonaceous materials more likely thandeactivation by carbon monoxide poisoning
Steady-state operation of the n-hexadecane fuel cellwithout additional deactivation was observed at one set of
8 Journal of Fuels
fuel cell operating conditionsThat observation demonstratesthat stable fuel cell operation is technically feasible whenn-hexadecane is the fuel at the anode of a fuel cell Itsuggests there ismerit in investigating fuel cell operationwithcommercial fuels such as petroleum diesel or biodiesel
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this research anddevelopment project was supported by a grant from Trans-port Canadarsquos Clean Rail Academic Grant Program and bya Discovery Grant from the Canadian Governmentrsquos NaturalSciences and Engineering Research Council
References
[1] J A A Ketelaar ldquoHistoryrdquo in Fuel Cell Systems L JM J Blomenand M N Mugerwa Eds p 20 Plenum Press New York NYUSA 1993
[2] E J Cairns ldquoAnodic oxidation of hydrocarbons and thehydrocarbon fuel cellrdquoAdvances in Electrochemistry Science andElectrochemical Engineering vol 8 pp 337ndash392 1971
[3] J O M Bockris and S Srinivasan ldquoElectrochemical combus-tion of organic substancesrdquo in Fuel CellsTheir Electrochemistrypp 357ndash411 McGraw-Hill New York NY USA 1969
[4] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 458ndash523 John Wiley amp Sons New York NY USA 1968
[5] S Bertholet Oxydation Electrocatalytique du Methane [PhDDissertation] Universite de Poitiers Poitiers France 1998
[6] C K Cheng J L Luo K T Chuang and A R SangerldquoPropane fuel cells using phosphoric-acid-doped polybenzim-idazole membranesrdquo The Journal of Physical Chemistry B vol109 no 26 pp 13036ndash13042 2005
[7] O Savadogo and F J Rodriguez Varela ldquoLow-temperaturedirect propane polymer electrolyte membranes fuel cellrdquo Jour-nal of New Materials for Electrochemical Systems vol 4 no 2pp 93ndash97 2001
[8] F J Rodrıguez Varela and O Savadogo ldquoReal-time massspectrometric analysis of the anode exhaust gases of a directpropane fuel cellrdquo Journal of the Electrochemical Society vol 152no 9 pp A1755ndashA1762 2005
[9] P Heo K Ito A Tomita and T Hibino ldquoA proton-conductingfuel cell operating with hydrocarbon fuelsrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7841ndash78442008
[10] B C H Steele I Kelly H Middleton and R Rudkin ldquoOxida-tion of methane in solid state electrochemical reactorsrdquo SolidState Ionics vol 28ndash30 no 2 pp 1547ndash1552 1988
[11] E P Murray T Tsai and S A Barnett ldquoA direct-methane fuelcell with a ceria-based anoderdquo Nature vol 400 no 6745 pp649ndash651 1999
[12] W Zhu C Xia J Fan R Peng and G Meng ldquoCeria coated Nias anodes for direct utilization of methane in low-temperature
solid oxide fuel cellsrdquo Journal of Power Sources vol 160 no 2pp 897ndash902 2006
[13] M D Gross J M Vohs and R J Gorte ldquoRecent progress inSOFC anodes for direct utilization of hydrocarbonsrdquo Journal ofMaterials Chemistry vol 17 no 30 pp 3071ndash3077 2007
[14] J G Lee C M Lee M Park and Y G Shul ldquoDirect methanefuel cell with La
2Sn2O7ndashNindashGd
01Ce09O195
anode and electro-spun La
06Sr04Co02Fe08O3minus120575
ndashGd01Ce09O195
cathoderdquo RoyalSociety of Chemistry Advances vol 3 no 29 pp 11816ndash118222013
[15] D Ding Z Liu L Li andC Xia ldquoAn octane-fueled low temper-ature solid oxide fuel cell with Ru-free anodesrdquo ElectrochemistryCommunications vol 10 no 9 pp 1295ndash1298 2008
[16] H Kishimoto K Yamaji T Horita et al ldquoFeasibility of liquidhydrocarbon fuels for SOFC with Ni-ScSZ anoderdquo Journal ofPower Sources vol 172 no 1 pp 67ndash71 2007
[17] Z F Zhou C Gallo M B Pague H Schobert and S N LvovldquoDirect oxidation of jet fuels and Pennsylvania crude oil in asolid oxide fuel cellrdquo Journal of Power Sources vol 133 no 2 pp181ndash187 2004
[18] G Psofogiannakis Y Bourgault B E Conway and M TernanldquoMathematical model for a direct propane phosphoric acid fuelcellrdquo Journal of Applied Electrochemistry vol 36 no 1 pp 115ndash130 2006
[19] H Khakdaman Y Bourgault and M Ternan ldquoComputationalmodeling of a direct propane fuel cellrdquo Journal of Power Sourcesvol 196 no 6 pp 3186ndash3194 2011
[20] H R Khakdaman Y Bourgault and M Ternan ldquoDirectpropane fuel cell anode with interdigitated flow fields two-dimensional modelrdquo Industrial amp Engineering ChemistryResearch vol 49 no 3 pp 1079ndash1085 2010
[21] G Psofogiannakis A St-Amant andM Ternan ldquoAb-initioDFTstudy of methane electro-oxidation mechanism on platinumrdquoJournal of Physical Chemistry B vol 110 pp 24593ndash24605 2006
[22] S Vafaeyan A St-Amant andM Ternan ldquoNickel alloy catalystsfor the anode of a high temperature PEM direct propane fuelcellrdquo Journal of Chemistry vol 2014 Article ID 151638 8 pages2014
[23] S Vafaeyan A St-Amant and M Ternan ldquoPropane fuel cellsselectivity for partial or complete reactionrdquo Journal of Fuels vol2014 Article ID 485045 9 pages 2014
[24] A Al-Othman A Y Tremblay W Pell et al ldquoA modified silicicacid (Si) and sulphuric acid (S)-ZrPPTFEglycerol compositemembrane for high temperature direct hydrocarbon fuel cellsrdquoJournal of Power Sources vol 224 pp 158ndash167 2013
[25] A Al-Othman A Y Tremblay W Pell Y Liu B A Peppleyand M Ternan ldquoThe effect of glycerol on the conductivity ofNafion-free ZrPPTFE composite membrane electrolytes fordirect hydrocarbon fuel cellsrdquo Journal of Power Sources vol 199pp 14ndash21 2012
[26] A Al-Othman A Y Tremblay W Pell et al ldquoZirconium phos-phate as the proton conducting material in direct hydrocarbonpolymer electrolyte membrane fuel cells operating above theboiling point of waterrdquo Journal of Power Sources vol 195 no9 pp 2520ndash2525 2010
[27] C G Farrell C L Gardner and M Ternan ldquoExperimental andmodelling studies of CO poisoning in PEM fuel cellsrdquo Journalof Power Sources vol 171 no 2 pp 282ndash293 2007
[28] R Fonocho C L Gardner and M Ternan ldquoA study of theelectrochemical hydrogenation of o-xylene in a PEM hydro-genation reactorrdquo Electrochimica Acta vol 75 pp 171ndash178 2012
Journal of Fuels 9
[29] N Sammes R Bove and K Stahl ldquoPhosphoric acid fuel cellsfundamentals and applicationsrdquo Current Opinion in Solid Stateand Materials Science vol 8 no 5 pp 372ndash378 2004
[30] J M King and H R Kunz ldquoPhosphoric acid electrolyte fuelcellsrdquo in Handbook of Fuel Cells W Vielstich A Lamm HA Gasteiger and H Yokokawa Eds vol 1 pp 287ndash300 JohnWiley amp Sons New York NY USA 2010
[31] S R Choudhury ldquoPhosphoric acid fuel cell technologyrdquo inRecent Trends in Fuel Cell Science and Technology S Basu Edpp 188ndash216 Springer New York NY USA 2007
[32] W Grubb and C J Michalske ldquoA high performance propanefuel cell operating in the temperature range of 150∘ndash200∘CrdquoJournal of The Electrochemical Society vol 111 no 9 p 10151964
[33] H A Liebhafsky andW T Grubb ldquoNormal alkanes at platinumanodesrdquo Fuel Preprints vol 11 no 2 p 134 1967
[34] V S Bagotzky Y B Vassiliev and O A Khazova ldquoGeneralizedscheme of chemisorption electrooxidation and electroreduc-tion of simple organic compounds on platinum group metalsrdquoJournal of Electroanalytical Chemistry and Interfacial Electro-chemistry vol 81 no 2 pp 229ndash238 1977
[35] T F Fuller F J Luczak and D J Wheeler ldquoElectrocatalystutilization in phosphoric acid fuel cellsrdquo Journal of the Electro-chemical Society vol 142 no 6 pp 1752ndash1757 1995
[36] E H Okrent and C E Heath ldquoA liquid hydrocarbon fuel cellbatteryrdquo in Fuel Cell Systems B Baker Ed Advances in Chem-istry pp 328ndash340 American Chemical Society WashingtonDC USA 1969
[37] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 485ndash510 John Wiley amp Sons New York NY USA 1968
[38] H Kim S Park J M Vohs and R J Gorte ldquoDirect oxidationof liquid fuels in a solid oxide fuel cellrdquo Journal of the Electro-chemical Society vol 148 no 7 pp A693ndashA695 2001
[39] S Islam and J M Hill ldquoBarium oxide promoted NiYSZ solid-oxide fuel cells for direct utilization of methanerdquo Journal ofMaterials Chemistry A vol 2 no 6 pp 1922ndash1929 2014
[40] C Yang J Li Y Lin J Liu F Chen and M Liu ldquoIn-situfabrication of CoFe allot nanoparticles structure (Pr
04Sr06)3
(Fe085
Nb015
)O7ceramic anode for direct hydrocarbon solid
oxde fuel cellsrdquo Nano Energy vol 11 pp 704ndash711 2015[41] S McIntosh and R J Gorte ldquoDirect hydrocarbon solid oxide
fuel cellsrdquo Chemical Reviews vol 104 no 10 pp 4845ndash48652004
[42] Y Zhao C Xia L Jia et al ldquoRecent progress on solid oxide fuelcell lowering temperature and utilizing non-hydrogen fuelsrdquoInternational Journal of Hydrogen Energy vol 38 no 36 pp16498ndash16517 2013
[43] S Srinivasan Fuel Cells From Fundamentals to ApplicationsSpringer New York NY USA 2006
[44] M RWalluk J LinMGWaller D F Smith andTA TraboldldquoDiesel auto-thermal reforming for solid oxide fuel cell systemsanode off-gas recycle simulationrdquo Applied Energy vol 130 pp94ndash102 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
8 Journal of Fuels
fuel cell operating conditionsThat observation demonstratesthat stable fuel cell operation is technically feasible whenn-hexadecane is the fuel at the anode of a fuel cell Itsuggests there ismerit in investigating fuel cell operationwithcommercial fuels such as petroleum diesel or biodiesel
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
The authors gratefully acknowledge that this research anddevelopment project was supported by a grant from Trans-port Canadarsquos Clean Rail Academic Grant Program and bya Discovery Grant from the Canadian Governmentrsquos NaturalSciences and Engineering Research Council
References
[1] J A A Ketelaar ldquoHistoryrdquo in Fuel Cell Systems L JM J Blomenand M N Mugerwa Eds p 20 Plenum Press New York NYUSA 1993
[2] E J Cairns ldquoAnodic oxidation of hydrocarbons and thehydrocarbon fuel cellrdquoAdvances in Electrochemistry Science andElectrochemical Engineering vol 8 pp 337ndash392 1971
[3] J O M Bockris and S Srinivasan ldquoElectrochemical combus-tion of organic substancesrdquo in Fuel CellsTheir Electrochemistrypp 357ndash411 McGraw-Hill New York NY USA 1969
[4] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 458ndash523 John Wiley amp Sons New York NY USA 1968
[5] S Bertholet Oxydation Electrocatalytique du Methane [PhDDissertation] Universite de Poitiers Poitiers France 1998
[6] C K Cheng J L Luo K T Chuang and A R SangerldquoPropane fuel cells using phosphoric-acid-doped polybenzim-idazole membranesrdquo The Journal of Physical Chemistry B vol109 no 26 pp 13036ndash13042 2005
[7] O Savadogo and F J Rodriguez Varela ldquoLow-temperaturedirect propane polymer electrolyte membranes fuel cellrdquo Jour-nal of New Materials for Electrochemical Systems vol 4 no 2pp 93ndash97 2001
[8] F J Rodrıguez Varela and O Savadogo ldquoReal-time massspectrometric analysis of the anode exhaust gases of a directpropane fuel cellrdquo Journal of the Electrochemical Society vol 152no 9 pp A1755ndashA1762 2005
[9] P Heo K Ito A Tomita and T Hibino ldquoA proton-conductingfuel cell operating with hydrocarbon fuelsrdquo AngewandteChemiemdashInternational Edition vol 47 no 41 pp 7841ndash78442008
[10] B C H Steele I Kelly H Middleton and R Rudkin ldquoOxida-tion of methane in solid state electrochemical reactorsrdquo SolidState Ionics vol 28ndash30 no 2 pp 1547ndash1552 1988
[11] E P Murray T Tsai and S A Barnett ldquoA direct-methane fuelcell with a ceria-based anoderdquo Nature vol 400 no 6745 pp649ndash651 1999
[12] W Zhu C Xia J Fan R Peng and G Meng ldquoCeria coated Nias anodes for direct utilization of methane in low-temperature
solid oxide fuel cellsrdquo Journal of Power Sources vol 160 no 2pp 897ndash902 2006
[13] M D Gross J M Vohs and R J Gorte ldquoRecent progress inSOFC anodes for direct utilization of hydrocarbonsrdquo Journal ofMaterials Chemistry vol 17 no 30 pp 3071ndash3077 2007
[14] J G Lee C M Lee M Park and Y G Shul ldquoDirect methanefuel cell with La
2Sn2O7ndashNindashGd
01Ce09O195
anode and electro-spun La
06Sr04Co02Fe08O3minus120575
ndashGd01Ce09O195
cathoderdquo RoyalSociety of Chemistry Advances vol 3 no 29 pp 11816ndash118222013
[15] D Ding Z Liu L Li andC Xia ldquoAn octane-fueled low temper-ature solid oxide fuel cell with Ru-free anodesrdquo ElectrochemistryCommunications vol 10 no 9 pp 1295ndash1298 2008
[16] H Kishimoto K Yamaji T Horita et al ldquoFeasibility of liquidhydrocarbon fuels for SOFC with Ni-ScSZ anoderdquo Journal ofPower Sources vol 172 no 1 pp 67ndash71 2007
[17] Z F Zhou C Gallo M B Pague H Schobert and S N LvovldquoDirect oxidation of jet fuels and Pennsylvania crude oil in asolid oxide fuel cellrdquo Journal of Power Sources vol 133 no 2 pp181ndash187 2004
[18] G Psofogiannakis Y Bourgault B E Conway and M TernanldquoMathematical model for a direct propane phosphoric acid fuelcellrdquo Journal of Applied Electrochemistry vol 36 no 1 pp 115ndash130 2006
[19] H Khakdaman Y Bourgault and M Ternan ldquoComputationalmodeling of a direct propane fuel cellrdquo Journal of Power Sourcesvol 196 no 6 pp 3186ndash3194 2011
[20] H R Khakdaman Y Bourgault and M Ternan ldquoDirectpropane fuel cell anode with interdigitated flow fields two-dimensional modelrdquo Industrial amp Engineering ChemistryResearch vol 49 no 3 pp 1079ndash1085 2010
[21] G Psofogiannakis A St-Amant andM Ternan ldquoAb-initioDFTstudy of methane electro-oxidation mechanism on platinumrdquoJournal of Physical Chemistry B vol 110 pp 24593ndash24605 2006
[22] S Vafaeyan A St-Amant andM Ternan ldquoNickel alloy catalystsfor the anode of a high temperature PEM direct propane fuelcellrdquo Journal of Chemistry vol 2014 Article ID 151638 8 pages2014
[23] S Vafaeyan A St-Amant and M Ternan ldquoPropane fuel cellsselectivity for partial or complete reactionrdquo Journal of Fuels vol2014 Article ID 485045 9 pages 2014
[24] A Al-Othman A Y Tremblay W Pell et al ldquoA modified silicicacid (Si) and sulphuric acid (S)-ZrPPTFEglycerol compositemembrane for high temperature direct hydrocarbon fuel cellsrdquoJournal of Power Sources vol 224 pp 158ndash167 2013
[25] A Al-Othman A Y Tremblay W Pell Y Liu B A Peppleyand M Ternan ldquoThe effect of glycerol on the conductivity ofNafion-free ZrPPTFE composite membrane electrolytes fordirect hydrocarbon fuel cellsrdquo Journal of Power Sources vol 199pp 14ndash21 2012
[26] A Al-Othman A Y Tremblay W Pell et al ldquoZirconium phos-phate as the proton conducting material in direct hydrocarbonpolymer electrolyte membrane fuel cells operating above theboiling point of waterrdquo Journal of Power Sources vol 195 no9 pp 2520ndash2525 2010
[27] C G Farrell C L Gardner and M Ternan ldquoExperimental andmodelling studies of CO poisoning in PEM fuel cellsrdquo Journalof Power Sources vol 171 no 2 pp 282ndash293 2007
[28] R Fonocho C L Gardner and M Ternan ldquoA study of theelectrochemical hydrogenation of o-xylene in a PEM hydro-genation reactorrdquo Electrochimica Acta vol 75 pp 171ndash178 2012
Journal of Fuels 9
[29] N Sammes R Bove and K Stahl ldquoPhosphoric acid fuel cellsfundamentals and applicationsrdquo Current Opinion in Solid Stateand Materials Science vol 8 no 5 pp 372ndash378 2004
[30] J M King and H R Kunz ldquoPhosphoric acid electrolyte fuelcellsrdquo in Handbook of Fuel Cells W Vielstich A Lamm HA Gasteiger and H Yokokawa Eds vol 1 pp 287ndash300 JohnWiley amp Sons New York NY USA 2010
[31] S R Choudhury ldquoPhosphoric acid fuel cell technologyrdquo inRecent Trends in Fuel Cell Science and Technology S Basu Edpp 188ndash216 Springer New York NY USA 2007
[32] W Grubb and C J Michalske ldquoA high performance propanefuel cell operating in the temperature range of 150∘ndash200∘CrdquoJournal of The Electrochemical Society vol 111 no 9 p 10151964
[33] H A Liebhafsky andW T Grubb ldquoNormal alkanes at platinumanodesrdquo Fuel Preprints vol 11 no 2 p 134 1967
[34] V S Bagotzky Y B Vassiliev and O A Khazova ldquoGeneralizedscheme of chemisorption electrooxidation and electroreduc-tion of simple organic compounds on platinum group metalsrdquoJournal of Electroanalytical Chemistry and Interfacial Electro-chemistry vol 81 no 2 pp 229ndash238 1977
[35] T F Fuller F J Luczak and D J Wheeler ldquoElectrocatalystutilization in phosphoric acid fuel cellsrdquo Journal of the Electro-chemical Society vol 142 no 6 pp 1752ndash1757 1995
[36] E H Okrent and C E Heath ldquoA liquid hydrocarbon fuel cellbatteryrdquo in Fuel Cell Systems B Baker Ed Advances in Chem-istry pp 328ndash340 American Chemical Society WashingtonDC USA 1969
[37] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 485ndash510 John Wiley amp Sons New York NY USA 1968
[38] H Kim S Park J M Vohs and R J Gorte ldquoDirect oxidationof liquid fuels in a solid oxide fuel cellrdquo Journal of the Electro-chemical Society vol 148 no 7 pp A693ndashA695 2001
[39] S Islam and J M Hill ldquoBarium oxide promoted NiYSZ solid-oxide fuel cells for direct utilization of methanerdquo Journal ofMaterials Chemistry A vol 2 no 6 pp 1922ndash1929 2014
[40] C Yang J Li Y Lin J Liu F Chen and M Liu ldquoIn-situfabrication of CoFe allot nanoparticles structure (Pr
04Sr06)3
(Fe085
Nb015
)O7ceramic anode for direct hydrocarbon solid
oxde fuel cellsrdquo Nano Energy vol 11 pp 704ndash711 2015[41] S McIntosh and R J Gorte ldquoDirect hydrocarbon solid oxide
fuel cellsrdquo Chemical Reviews vol 104 no 10 pp 4845ndash48652004
[42] Y Zhao C Xia L Jia et al ldquoRecent progress on solid oxide fuelcell lowering temperature and utilizing non-hydrogen fuelsrdquoInternational Journal of Hydrogen Energy vol 38 no 36 pp16498ndash16517 2013
[43] S Srinivasan Fuel Cells From Fundamentals to ApplicationsSpringer New York NY USA 2006
[44] M RWalluk J LinMGWaller D F Smith andTA TraboldldquoDiesel auto-thermal reforming for solid oxide fuel cell systemsanode off-gas recycle simulationrdquo Applied Energy vol 130 pp94ndash102 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Journal of Fuels 9
[29] N Sammes R Bove and K Stahl ldquoPhosphoric acid fuel cellsfundamentals and applicationsrdquo Current Opinion in Solid Stateand Materials Science vol 8 no 5 pp 372ndash378 2004
[30] J M King and H R Kunz ldquoPhosphoric acid electrolyte fuelcellsrdquo in Handbook of Fuel Cells W Vielstich A Lamm HA Gasteiger and H Yokokawa Eds vol 1 pp 287ndash300 JohnWiley amp Sons New York NY USA 2010
[31] S R Choudhury ldquoPhosphoric acid fuel cell technologyrdquo inRecent Trends in Fuel Cell Science and Technology S Basu Edpp 188ndash216 Springer New York NY USA 2007
[32] W Grubb and C J Michalske ldquoA high performance propanefuel cell operating in the temperature range of 150∘ndash200∘CrdquoJournal of The Electrochemical Society vol 111 no 9 p 10151964
[33] H A Liebhafsky andW T Grubb ldquoNormal alkanes at platinumanodesrdquo Fuel Preprints vol 11 no 2 p 134 1967
[34] V S Bagotzky Y B Vassiliev and O A Khazova ldquoGeneralizedscheme of chemisorption electrooxidation and electroreduc-tion of simple organic compounds on platinum group metalsrdquoJournal of Electroanalytical Chemistry and Interfacial Electro-chemistry vol 81 no 2 pp 229ndash238 1977
[35] T F Fuller F J Luczak and D J Wheeler ldquoElectrocatalystutilization in phosphoric acid fuel cellsrdquo Journal of the Electro-chemical Society vol 142 no 6 pp 1752ndash1757 1995
[36] E H Okrent and C E Heath ldquoA liquid hydrocarbon fuel cellbatteryrdquo in Fuel Cell Systems B Baker Ed Advances in Chem-istry pp 328ndash340 American Chemical Society WashingtonDC USA 1969
[37] H A Liebhafsky and E J Cairns ldquoThe direct hydrocarbon fuelcell with aqueous electrolytesrdquo in Fuel Cells and Fuel Batteriespp 485ndash510 John Wiley amp Sons New York NY USA 1968
[38] H Kim S Park J M Vohs and R J Gorte ldquoDirect oxidationof liquid fuels in a solid oxide fuel cellrdquo Journal of the Electro-chemical Society vol 148 no 7 pp A693ndashA695 2001
[39] S Islam and J M Hill ldquoBarium oxide promoted NiYSZ solid-oxide fuel cells for direct utilization of methanerdquo Journal ofMaterials Chemistry A vol 2 no 6 pp 1922ndash1929 2014
[40] C Yang J Li Y Lin J Liu F Chen and M Liu ldquoIn-situfabrication of CoFe allot nanoparticles structure (Pr
04Sr06)3
(Fe085
Nb015
)O7ceramic anode for direct hydrocarbon solid
oxde fuel cellsrdquo Nano Energy vol 11 pp 704ndash711 2015[41] S McIntosh and R J Gorte ldquoDirect hydrocarbon solid oxide
fuel cellsrdquo Chemical Reviews vol 104 no 10 pp 4845ndash48652004
[42] Y Zhao C Xia L Jia et al ldquoRecent progress on solid oxide fuelcell lowering temperature and utilizing non-hydrogen fuelsrdquoInternational Journal of Hydrogen Energy vol 38 no 36 pp16498ndash16517 2013
[43] S Srinivasan Fuel Cells From Fundamentals to ApplicationsSpringer New York NY USA 2006
[44] M RWalluk J LinMGWaller D F Smith andTA TraboldldquoDiesel auto-thermal reforming for solid oxide fuel cell systemsanode off-gas recycle simulationrdquo Applied Energy vol 130 pp94ndash102 2014
