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Impact of pore size of ordered mesoporous carbonFDU-15-supported
platinum catalysts on oxygenreduction reaction
Gang Zhao, T.S. Zhao*, Jianbo Xu, Zeng Lin, Xiaohui Yan
Department of Mechanical and Aerospace Engineering, The Hong
Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong SAR, China
a r t i c l e i n f o
Article history:
Received 8 August 2016
Received in revised form
25 October 2016
Accepted 11 November 2016
Available online 1 December 2016
Keywords:
Ordered mesoporous carbons
FDU-15
Pore size
Platinum
Oxygen reduction reaction
* Corresponding author.E-mail address: [email protected] (T.S.
Zh
http://dx.doi.org/10.1016/j.ijhydene.2016.11.00360-3199/© 2016
Hydrogen Energy Publicati
a b s t r a c t
To investigate the impact of pore size of ordered mesoporous
carbon (OMC) FDU-15-
supported Platinum (Pt) catalysts on oxygen reduction reaction
(ORR), OMC FDU-15 with
various pore sizes ranging from 4.0 nm to 8.1 nm are synthesized
through a soft-template
method, and then FDU-15-supported Pt catalysts are prepared by
chemical impregnation
method. Characterizations show that increase in pore size
enlarges the specific surface
area and the pore volume of FDU-15, but decreases the electrical
conductivity. Particle size
of FDU-15-supported Pt catalyst is also influenced in a
decreasing trend with the increase
of pore size. Electrochemical measurement demonstrates that
FDU-15-supported Pt cata-
lyst with a pore size of 6.5 nm yields the highest
electrocatalytic activity for ORR, which is
further confirmed by single cell test on DMFC, as the catalyst
for cathode.
© 2016 Hydrogen Energy Publications LLC. Published by Elsevier
Ltd. All rights reserved.
Introduction
Platinum (Pt) is generally used as catalyst for oxygen
reduction
reaction (ORR) in proton exchange membrane fuel cell
(PEMFC) and direct methanol fuel cell (DMFC) for its
superior
activity and stability in acidic environment. However, due
to
the expensive price and the scarcity of Pt metal, cost-
ineffective of the system is unavoidable. To address this
issue, supported Pt catalyst rather than pure Pt catalyst is
used
for the improved utilization, which makes it possible to
decrease the total Pt amount needed. In this sense, an ideal
support with high specific surface area, high electrical
con-
ductivity and high resistance to corrosion is needed.
ao).89ons LLC. Published by Els
Generally, Activated carbons are widely used as support
materials for their low cost and extensive sources. Other
than
activated carbons, novel carbon materials such as carbon
nanotube [1e6], carbon nanofiber [7e13], and ordered meso-
porous carbon [14e28] have been reported to have potentials
to be used as support materials for their unique
morphologies
and high specific surface areas. Among the above-mentioned
carbonmaterials, ordered mesoporous carbon (OMC) is one of
the most promising support materials for their unique or-
dered and tailored nanostructure and narrow pore size dis-
tributions in mesopore range [29e39].
Ryoo et al. [40] first prepared OMC with MCM-48 silica as
hard template and sucrose as carbon source, through a nano-
casting method, also known as hard-template method. After
evier Ltd. All rights reserved.
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that, a family of OMCs, named CMK materials, was reported
by his group, including CMK-1 to CMK-5 by using different
templates. Joo et al. [41] first reported that Pt catalyst
sup-
ported on CMK-5 showed much higher activity for the ORR
than supported on carbon black. After that, extensive
efforts
have been made to improve the activity of OMC-supported Pt
catalyst by controlling the morphology and the pore size of
OMC. Joo et al. [42] synthesized OMCwith various pore size
by
using ordered mesoporous silicas with various pore size as
hard templates to investigated the effect of pore size of
OMC-
supported Pt catalyst's activity for ORR in DMFCs, and
foundlarger pore size is good for ORR. Lu et al. [43] prepared
OMC
with controllable pore sizes in the range of 4e10 nm bymeans
of a template procedure using 2D hexagonal MSU-H and 3D
cubic KIT-6 as the hard templates and boric acid as the pore
expanding agent; the analysis of two kinds of pore symme-
tries of OMC showed that the 3D cubic OMC demonstrated
superior capacitive performance than the 2D hexagonal OMC.
Song et al. [44] deposited Pt particles on CMK-3 with three
different pore sizes obtained by using boric acid as the
pore-
expanding agent, and investigated their effect on the
alcohol
electrooxidation activity, and found smaller pore size is
good
for alcohol electrooxidation activity, due to the enhanced
electric conductivity. Kim et al. [45] investigated the effect
of
different morphologies of OMC on ORR for supported Pt cat-
alystswith three types of OMC, including CMK-3, CMK-3G, and
CMK-5, and results indicated the Pt/CMK-3G exhibited the
highest kinetic current density and highest oxygen oxi-
dization reaction activity. D. Banham et al. [46e48] also
investigated the influence of morphology and pore size of
OMC on the supported Pt catalysts for their ORR activity by
using mesoporous silicas as templates, and indicated that
the
inner wall thickness of OMC is critical to the design of
support
materials. Apparently, pore size and morphology of OMC play
important roles on ORR performance, when OMC is used as
support materials for Pt catalysts.
It is noteworthy that above conclusions are based on the
CMK-type ordered mesoporous carbons, prepared from hard-
template route. The key drawback of this method lies in the
fact that extra steps are required to remove the hard
template,
making it expensive and time-consuming.
Different from the above mentioned hard-template
method, Meng et al. [49] proposed an evaporation-induced
self-assembly strategy to prepare OMC in 2006, known as
soft-template method. The resultant OMC is called FDU ma-
terials including FDU-15 (2-D hexagonal), FDU-14 (3-D
cubic),
FDU-16 (3-D bicontinuous). It is noted that FDU-15 is
completely the invert replicas of CMK-3, as shown in Fig. 1.
As
we know, research on CMK-3 used as support materials for Pt
catalyst has been thoroughly investigated; however that on
FDU-15 is seldom reported. Because of different morphologies
of FDU-15 and CMK-3 (Fig. 1), the previous conclusion on
CMK-
3 might not be right for FDU-15.
In this work, OMC FDU-15, acting as supports for Pt cata-
lysts, is prepared with resol and Pluronic F127 as carbon
pre-
cursor and soft template. Tetraethyl orthosilicate (TEOS)
and
decane are used as pore-expanding agents, so that FDU-15
with various pore sizes can be formed. Subsequently, FDU-
15-supported Pt catalysts are then prepared by chemical
impregnation method, with ethylene glycol (EG) as reducing
agent. Cyclic voltammetry (CV) and linear sweep voltammetry
(LSV) are conducted to evaluate the ORR performances of
supported Pt catalysts, and the impact of pore size is dis-
cussed. Finally, a single DMFC is fabricated by employing
the
as-prepared FDU-15 supported Pt catalysts as cathode cata-
lysts, and IeV performance and durability are tested.
Experimental
Preparation of OMC FDU-15 with different pore sizes
Preparation of OMC FDU-15 is according to the literature
[49].
Firstly, Resol isprepared toascarbonprecursor forOMCFDU-15.
Typically, 1.0 g of phenol, 0.21 g of NaOH (20 wt. %) and 1.7 g
of
formaldehydesolution (37wt.%)weremixedandheatedat75 �Cfor 1 h.
After cooled to room temperature, pH value of the
mixturewas controlled at 7.0with 1MofHCl solution.And then
water in themixturewas removed throughvacuumdistillation.
Ethanol was added to form the resol solution (20 wt. %).
When preparing FDU-15, 1.0 g of Pluronic F127 and 5.0 g of
resol were dissolved andmixed in 20.0 g of ethanol. After
that,
themixturewas transferred to a dish and evaporated for 8 h
at
room temperature, before heated at 100 �C for 24 h for
ther-mopolymerization. The resultant product was calcinated at
800 �C for 3 h in argon atmosphere at a rate of 1 �C min�1.
Theas-prepared sample was crashed to powders and denoted as
FDU-15-1.
To prepare FDU-15 with larger pore size, 1.0 g of TEOS [50]
was used as a pore-expanding agent and added into the
mixture before it was transferred to the dish. The following
steps were the same as those of FDU-15-1. The resultant
product was treated with 3 M KOH solution at 80 �C for 8 h
toremove silica. The final sample is denoted as FDU-15-2.
Decanewasusedasasecondpore-expandingagenttofurther
increase the pore size of FDU-15-2. 1.0 g and 2.0 g of
decanewere
added into the mixture after the adding of TEOS, and the
followingprocesswas the sameas inFDU-15-2. Theas-prepared
FDU-15 samples are denoted as FDU-15-3 and FDU-15-4.
Preparation of FDU-15-supported Pt catalysts
FDU-15-supported Pt catalysts were prepared by impregna-
tion method with EG as reducing agent [51e53]. Specifically,
3.38 mL of chloroplatinic acid EG solution (7.4 mgPt mL�1)
and
100 mg of FDU-15 carbon were dissolved and mixed in a
certain amount of EG, in which ratio of Pt is designed at
20 wt.%. 1 M of NaOH solution was subsequently added to
adjust the pH value of mixture to 12. After that, the
mixture
was heated to 140 �C for 3 h for the completely reduction of
Ptcatalyst. The final catalyst was obtained after filtering,
washing, and drying at 80 �C for 6e8 h in a vacuum oven.The
as-prepared Pt catalysts are denoted as Pt/FDU-15-1,
Pt/FDU-15-2, Pt/FDU-15-3, and Pt/FDU-15-4, according to the
supporting materials.
Physical characterizations
Nitrogen sorption isotherms were conducted on a Beckman
Coulter SA3100 surface area analyzer. BJH model was used to
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Fig. 1 e Schematic illustrations of FDU-15 (a) and CMK-3
(b).
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deduce the parameters of pore structure, in which the value
for the pore volume (Vt) was calculated by the adsorption
branches at a relative pressure of 0.9814 and pore size
distri-
bution was from the adsorption branches of the isotherms. X-
ray diffraction (XRD) measurement was recorded on an X'pertPro
(PANalytical) with Ni-filtered Cu Ka radiation. Thermog-
ravimetric (TG) test was measured on a TGAQ5000 from room
temperature to 800 �C under air flow with a ramp rate of5 �C
min�1. Transmission electron microscopy (TEM) imageswere obtained
from a TEM 2010F (JEOL), and the samples for
TEM test were prepared as follows: the samplewas suspended
in ethanol through ultrasonic oscillation and dropped onto a
holey carbon film supported on a Cu grid.
Measurements on electrical conductivity of the as-
prepared FDU-15 samples were according to the literature
[54,55]. Briefly, a certain amount of sample was pressed to
a
pellet under a fixed pressure, and then the pellet was
placed
between two gold plates, connected with an Autolab instru-
ment. Electrical conductivity of the sample was achieved by
impedance spectroscopy.
Electrochemical measurements
An Autolab instrument was employed for the electrochemical
measurements by using a Pt mesh as counter electrode and a
saturated calomel electrode (SCE) as reference electrode.
Working electrode was made by dispersing 2.0 mg of the as-
prepared catalyst and 15 mL of Nafion solution (5 wt.%) into
2.0 mL of ethanol under ultrasonication; and then 20 mL of
the
resultant ink was dropped onto a polished glassy carbon
electrode for several times and dried at ambient conditions.
CV measurements were obtained under nitrogen saturated
0.5 M H2SO4 solution. LSV measurements were conducted in
oxygen-saturated 0.5 M H2SO4 solution with a rotating speed
of 1600 rpm and a scan rate of 10 mV s�1 to examine the ox-ygen
reduction reaction (ORR).
Evaluation of single cell on DMFC
Preparation of membrane electrode assembly (MEA) for a
singleDMFCProcess of preparation of MEA for a single DMFC is
similar to
the previous work [56].
Typically, a certain amount of Vulcan XC-72 carbon and
20% PTFE were mixed in ethanol and ultrasonicated to get a
homogeneous ink; the resultant ink was brushed onto a PTFE-
treated Toray carbon paper until the loading of Vulcan XC-72
carbon reached 2mg cm�2, which served as diffusion layer forboth
anode and cathode. Catalyst layer was fabricated in a
similar way by mixing a certain amount of catalyst and 15%
Nafion in ethanol, the resultant catalyst ink was brushed
onto
the above as-prepared diffusion layer. For anode, commercial
60% PtRu/C (ratio of Pt:Ru is 1:1) from Johnson Matthey was
used as catalyst with a loading of 4 mg cm�2; for cathode,
theas-prepared FDU-15 supported Pt catalysts were used as cat-
alysts with an amount of 2 mg cm�2.
MEA was obtained by hot-pressing the anode and the
cathode on each side of a pretreated Nafion 115 membrane,
which included boiling for 1 h in 5 vol. % H2O2 at 80 �C
andanother 1 h in 0.5 M H2SO4 at 80 �C before washing it in
DIwater.
Test on single DMFCSingle DMFC was fabricated by fixing the MEA
between two
stainless steel plates with a single serpentine flow field
[56].
1 M of methanol solution and air from a cylinder were sup-
plied to the anode and the cathode of the DMFC with a flow
rate of 1 mL min�1 and 150 mL min�1, respectively. Temper-ature
of the DMFCwas kept at 75 �Cwith help of auxiliary heatsystem, and
an Arbin instrument was used as the electric
load.
Results and discussion
Physical characterization of the as-prepared OMC
FDU-15samples
The information of specific surface areas and pore size dis-
tributions of the FDU-15 samples were obtained from nitrogen
sorption isotherms. As shown in Fig. 2a, there is a
condensa-
tion at the middle range PS/P0 for all the samples, implying
a
pattern of type IV, confirming a typical mesoporous
structure
is formed with a narrow pore size distribution. The pore
size
distributions in Fig. 2b reveal an increasing trend of pore
size
from 4.0 nm to 5.5 nm, 6.5 nm, and 8.1 nm with the adding of
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Fig. 2 e Nitrogen sorption isotherms (a) and pore size
distribution (b) curves of the as-prepared OMC FDU-15 samples.
Fig. 3 e Small-angle XRD patterns of as-prepared OMC
FDU-15 samples.
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TEOS and decane. Table 1 provides the physical properties of
the as-prepared FDU-15 samples. The specific surface areas
(SBET) of OMC FDU-15 samples increase from 581 m2 g�1 to
921 m2 g�1, following the same trend of pore volume (Vt)
from0.443 mL g�1 to 1.329 mL g�1, suggesting that the increases
inthe specific surface areas and pore volumes are responses to
enlargement of the pore sizes from 4.0 nm to 8.1 nm. It is
noted that the function of TEOS is to mitigate the shrinkage
of
carbon framework during the process of carbonization, so
that
larger pore sizes can be retained [41]. However, further
addi-
tion of TEOS cannot further enlarge the pore size, but break
down the pore structure of FDU-15. So we have to resort to
another strategy. Decane was chosen as another swelling
agent because it can enlarge micelles in the solution which
ultimately settles as pores, so that pore size is enlarged
without any destruction on the pore structure.
Small-angle XRD patterns of the FDU-15 samples are
shown in Fig. 3. All samples demonstrate the main
diffraction
peaks [100] at 2q z 0.8�, indicating the presence of an
orderedmesoporous structure with a two-dimensional (2-D)
hexago-
nal symmetry. Furthermore, TEM images (Fig. 4aed) provide
an evidence of this unique textural structure of the as-
prepared samples in large domain with good regularities,
confirming the morphology of FDU-15. It is noteworthy that
pore sizes in Fig. 4aed illustrate an increasing trend, which
is
consistent with the results from the pore size distributions
in
nitrogen sorption isotherms.
Electrical conductivities for the as-prepared FDU-15 sam-
ples were measured to investigate the effect of pore size on
electrical conductivity, as shown in Table 1. It is found that
the
electrical conductivities of the FDU-15 samples decrease
from
4.46 to 2.21 S cm�1 with the increase of pore sizes from 4.0
to8.1 nm. The reason could be ascribed to that the increased
pore size undoubtedly leads to the growth of the pore volume
Table 1 e Physical properties of as-prepared OMC
FDU-15samples.
SBET (m2 g�1) Vt (mL g
�1) d (nm) s (S cm�1)
FDU-15-1 581 0.443 4.0 4.46
FDU-15-2 755 0.953 5.5 3.89
FDU-15-3 865 1.008 6.5 3.05
FDU-15-4 921 1.329 8.1 2.21
(Vt) and the porosity of FDU-15 samples, which inevitably
decreases the electrical conductivity.
Characterization of FDU-15-supported Pt catalysts
XRD patterns of FDU-15-supported Pt catalysts are
illustrated
in Fig. 5. All catalysts show individual [111], [200], [220],
and
[311] diffraction peaks at 2q z 39.9�, 46.1�, 67.8�, and
81.4�
respectively, in line with the reflections of a typical Pt
nano-
crystal exhibiting a face-centered cubic phase. Generally,
Sherrer equation is used to calculate the average particle
size
of Pt particles from the peak of [220] at 2q z 67.8� or [111] at
2q z 39.9�. However, [220] peaks of Pt crystals for the as-prepared
supported Pt catalysts are so small that it is diffi-
cult for Sherrer equation to calculate the average particle
size
of Pt catalysts, implying very small average Pt particle sizes
for
all the samples. On the other hand, the [111] peaks of Pt
cat-
alysts are suffered from the disturbance of the [200] peaks of
Pt
catalysts at 2q z 46.1� and the [100] reflection of pure
FDU-15at 2q z 43.80�, according to our previous work [57], making
itimpractical to calculate the particle size from XRD patterns.
TG analyseswere conducted to determine the amount of Pt
in the as-prepared Pt catalysts. According to Fig. 6, all the
Pt
catalysts showed a same behavior of losing weight dramati-
cally in the temperature range from 400 �C to 500 �C, due to
the
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Fig. 4 e TEM images of as-prepared FDU-15-1 (a), FDU-15-2 (b),
FDU-15-3 (c), and FDU-15-4 (d).
Fig. 5 e XRD patterns of FDU-15-supported Pt catalysts. Fig. 6 e
TG analyses of Pt catalysts.
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carbon oxidization. It can be concluded that the Pt amounts
in
the Pt catalysts are quite similar from 18.85% to 20.65%,
which
is consistent with the experimental design (20%), indicating
the loss of Pt in the process of experimental can be
neglected.
TEM images of FDU-15-supported Pt catalysts are shown in
Fig. 7aed. The sharp contrasts in TEM images clearly show
the
morphologies of FDU-15 and Pt particles. Domains of 2-D or-
dered hexagonal arrays can be observed in all the
as-prepared
catalysts, suggesting that the unique pore structure of
FDU-15
is preserved during Pt catalyst preparation. For all the
supported Pt catalysts, Pt particles are well dispersed on
the
surface of the FDU-15 without severe agglomeration. Based on
the measurements of 200 particles in random regions, the
average Pt particle sizes in Pt/FDU-15-1, Pt/FDU-15-2,
Pt/FDU-
15-3, and Pt/FDU-15-4 are estimated to be 2.9 nm, 2.3 nm,
2.0 nm, and 2.0 nm respectively (Fig. 7eef). The
corresponding
histograms reveal that the Pt particle size distributions
are
rather narrow and illustrate the typical features of a
Gaussian
distribution. Interestingly, the declining trend of the
average
Pt particle size is the opposite to that of the pore size and
the
specific surface areas. In addition, the dominant Pt
particle
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Fig. 7 e TEM images of Pt particles in Pt/FDU-15-1 (a),
Pt/FDU-15-2 (b), Pt/FDU-15-3 (c), and Pt/FDU-15-4 (d), and particle
size
distributions of the four samples (eef).
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sizes for Pt/FDU-15-3 and Pt/FDU-15-4 are similar. A likely
explanation is that the specific area of FDU-15 enlarges in
response to an increase in the pore size, ensuring a better
dispersion of Pt particles on the larger surface area of the
FDU-
15 samples. However, when the pore size of FDU-15 reaches a
value greater than 6.5 nm, the particle size of the FDU-15-
supported Pt catalysts become independent to the specific
surface area of the FDU-15 samples, while related to the
preparation method and the amount of Pt's loading. Thus,
thedominant Pt particle sizes remain similar (2.0 nm) for the
last
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Table 2 e Electrochemical properties of as-prepared
FDU-15-supported Pt catalysts.
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two samples, despite that the pore size increases from 6.5
nm
(FDU-15-3) to 8.1 nm (FDU-15-4).
Sample Pt particle size(nm)
SECSA(m2 g�1)
Eonset(V)
ikin(mA mg�1)
Pt/FDU-15-1 2.9 47.1 0.98 138
Pt/FDU-15-2 2.3 54.1 1.0 189
Pt/FDU-15-3 2.0 70.2 1.02 276
Pt/FDU-15-4 2.0 63.4 1.02 235
Electrochemical measurements of the supported Pt catalysts
CV measurements were performed for the as-prepared Pt
catalysts in nitrogen-saturated 0.5 M H2SO4 solution. It is
clear
that hydrogen underpotential deposition area could be seen
for all the samples, indicating a typical behavior of Pt
catalyst
in acid environment, as illustrated in Fig. 8a. We can
calculate
the value of electrochemical surface area (SECSA) by
integrating
the charge (Q) in hydrogen underpotential deposition with
the
following Eq. (1):
SECSA ¼ Qm� C (1)
where SECSA is the electrochemical surface area for Pt
catalyst,
Q is the integrated charges in hydrogen underpotential depo-
sition area, inwhich the double capacity charge is
deducted,m
is the Ptmass, andC is thehydrogenunderpotential deposition
constant on the smooth Pt surface (0.21 mC cm�2).Accordingly,
the values of SECSA for the FDU-15-supported
Pt catalysts are 47.1 m2 g�1Pt (Pt/FDU-15-1), 54.1 m2 g�1Pt
(Pt/
FDU-15-2), 70.2 m2 g�1Pt (Pt/FDU-15-3) and 63.4 m2 g�1Pt
(Pt/
FDU-15-4) respectively. With the increase in pore size, the
value of SECSA also enlarges, caused by the decreasing trend
of
Pt particle size. The peak value of the SECSA is as high as
70.2m2 g�1Pt, with the Pt catalyst supported on FDU-15with
anaverage pore size of 6.5 nm. However, the value of SECSA de-
clines to 63.4 m2 g�1Pt with a pore size of 8.1 nm. As
discussedin 3.2, when the pore size is under 6.5 nm, the increase
of pore
size results in the smaller Pt particle size of the
as-prepared
FDU-15-supported Pt catalysts yielding a larger value of
SECSA. However, the particle size of Pt catalyst remains
con-
stant when the pore size becomes larger than 6.5 nm. In
addition, an increase in pore size of FDU-15 tends to
decrease
the electrical conductivity, in response to increased
porosity,
as shown in Table 1. Therefore, combined the above
mentioned effects, the peak value of the SECSA was reached
with the pore size of 6.5 nm.
LSV measurements are conducted to compare the effect of
pore size on the ORR performances (Fig. 8b). The onset po-
tential of FDU-15-supported Pt catalysts moves slightly
posi-
tively with an increase in the pore size of FDU-15 samples,
Fig. 8 e CV (a) and LSV (b) curves of FDU-15-sup
which is consistent with the trend of the average Pt
particle
sizes' decreasing (Table 2). The onset potentials for
Pt/FDU-15-3 and Pt/FDU-15-4 are almost the same (1.02 V), explained
by
the fact that they both have similar average Pt particle
sizes.
The ORR mass activities at 0.9 V of the as-prepared samples
can be calculated from following equation:
MAðmass activityÞ ¼ ikin ¼ ilim*iobvilim � iobv (2)
where ikin is the kinetic current density, ilim is the
limiting
diffusion current density, and iobv is the current density at
the
potential of 0.9 V. The highest mass activity (276 mA mg�1Pt)can
be attained when the pore size is 6.5 nm, consistent with
its largest value of SECSA (70.2 m2 g�1). Although the
dominant
Pt particles' size in Pt/FDU-15-4 is the similar as those in
Pt/FDU-15-3, the mass activity declines as a result of the
decreased value of SECSA (Table 2).
Therefore, the pore size of FDU-15 has a close impact on
the ORR mass activity for the as-prepared FDU-15-supported
Pt catalysts. First of all, the increase of pore size leads to
the
enlargement of the specific surface area and the pore
volume,
which provides more sites for Pt deposition, and brings
about
smaller Pt particle size. However, the electrical
conductivity
reduces with the increase of pore size, as a negative
respect.
Combined with the advantage and disadvantage, the highest
mass activity of FDU-15-supported Pt catalyst was achieved
with the pore size of 6.5 nm.
Single cell test
ORR is generally the cathode reaction for PEMFCs and DMFCs.
Therefore, single cell test onDMFCwas used to further
evaluate
the impact of pore size on the performance of DMFC, in which
theas-preparedFDU-15-supportedPt catalystswereusedas the
ported Pt catalysts in 0.5 M H2SO4 solution.
http://dx.doi.org/10.1016/j.ijhydene.2016.11.089http://dx.doi.org/10.1016/j.ijhydene.2016.11.089
-
Fig. 9 e IeV curves (a) and power density (b) of a single DMFC
cell with as-prepared FDU-15-supported Pt catalysts as
cathode catalysts, and stability test of Pt/FDU-15-3 in single
cell at a constant current density of 0.1 A cm¡2 (ced).
i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e
r g y 4 2 ( 2 0 1 7 ) 3 3 2 5e3 3 3 43332
catalysts for cathode of DMFC. According to Fig. 9aeb, the
best
performance was obtained from the sample of Pt/FDU-15-3,
with a highest peak power density of 0.141 W cm�2. The trendin
single cell test is highly consistent with that in the electro-
chemical measurement, implying the reason should be the
combination of particle size of Pt catalysts and electrical
con-
ductivity, which caused by pore size of FDU-15. In addition,
the
difference in the area of mass transportation of IeV curves
shouldbecausedby thevariety ofpore size, inwhich largerpore
size brings about larger limiting current density.
As the best catalyst in this study, stability test was also
conducted for the Pt/FDU-15-3 by operating the single cell
for
continuously 73 h at a current density of 0.1 A cm�2,
compared
with that of commercial 20% Pt/C from E-TEK. According to
Fig. 9ced, the voltage of the single cell changes from 0.534 V
to
0.471 V in the continuously 73 h's operation, decreased by12.9%,
which is very similar to that of the commercial Pt
catalyst, implying a similar degradation rate. The cell
voltage
of Pt/FDU-15-3 is a little higher than that of the commercial
Pt
catalyst, possibly due to the optimized pore size.
Therefore,
this result shows thegreatpotential of theas-preparedPt/FDU-
15-3 as the catalyst for cathode in DMFC, compared with the
commercial Pt catalyst. It is noted that the measured degra-
dation rate is a little different from that of the literature
[58,59],
which may be caused by the difference test condition used.
Conclusion
In this paper, impact of pore size of FDU-15-supported Pt
catalyst is investigated by adopting a soft-template method.
The FDU-15 samples with four different pore sizes, ranging
from 4.0 nm to 8.1 nm, are prepared by the addition of pore-
expanding agents. By using the above FDU-15 samples as
supports, Pt catalysts are synthesized by the impregnation
method, with EG as the reducing agent. The relationship be-
tween the pore size of FDU-15 and the ORR activity of
FDU-15-
supported Pt catalysts is studied. It is noted that the pore
size
of FDU-15 has an influence on the electrical conductivity
and
the particle size of Pt catalysts. CV and LSV measurements
illustrate that the FDU-15-supported Pt catalyst with a pore
size of 6.5 nm delivers the largest value of SECSA (70.2 m2
g�1)
and the highest ORR mass activity at 0.9 V (276 mA
mg�1Pt).Single cell test on DMFC further confirms the best
perfor-
mance is achieved from the single cell which Pt/FDU-15-3
(6.5 nm) is used as the cathode catalyst.
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Impact of pore size of ordered mesoporous carbon
FDU-15-supported platinum catalysts on oxygen reduction
reactionIntroductionExperimentalPreparation of OMC FDU-15 with
different pore sizesPreparation of FDU-15-supported Pt
catalystsPhysical characterizationsElectrochemical
measurementsEvaluation of single cell on DMFCPreparation of
membrane electrode assembly (MEA) for a single DMFCTest on single
DMFC
Results and discussionPhysical characterization of the
as-prepared OMC FDU-15 samplesCharacterization of FDU-15-supported
Pt catalystsElectrochemical measurements of the supported Pt
catalystsSingle cell test
ConclusionReferences
