KMU 401 CHEMICAL ENGINEERING BASIC
MEASUREMENTS LABORATORY
EXPERIMENT 9:FUEL CELLS
Instructor: Bilginur Maraş
Group P5: Buket İBİDAN 20824096
Damla TAŞFİLİZ 20824283
Özgün UÇAK 20824341
Date of experiment : 19.11.2012
Date of submission : 26.11.2012
26.11.2012
Dear Prof.Dr. Zümriye Aksu
The experiment ‘‘Fuel Cells’’ had been done in 19 November,2012. In this experiment five
different experiments were made. For these experiments electrolyser, solar module, hydrogen
fuel cell, load measurement box and lamp were used.Essential aim of the experiment was
getting information about significative features of; solar cell, electrolysers and fuel cells;
learning types and importance of semiconductors in designing solar cells, improvement
methods of semiconductors and p-n juctions, working principles of different types of
electrolysers and fuel cells, different reactions which occur in anode and cathode of
electrolysers and fuel cells, energy supply, current, and power change with resistance in cell
circuits.
Research Assistant Bilginur Maraş was contributed to our work during the experiment. The
experiment had been taken about four hours. This experiment has some errors in first and
second part of experiment such as in first of it Faraday Efficiency is lower than actuall value .
If the system works successfully and all the conditions are perfect, Faraday Efficiency would
possibly be 100%. But as extra voltage shows that there is a loss of efficiency. To eliminate
this problem, the surface area should increased or it should be less thick.This experiment was
done well disciplined and carefully. Also in second experiment, the difference between the
theoretical actual value of this voltage depends on several parameters, e.g. The type and
composition of the electrode material, the electrolyte and the temperature.
Against all of the errors this experiment was made disciplined and carefully.
Buket İBİDAN Damla TAŞFİLİZ Özgün UÇAK
TABLE of CONTENTS
Cover Page.......................................................................................................................iii
Presentation Letter...........................................................................................................i
Table Of Contents............................................................................................................
Summary...........................................................................................................................ii
1 Theory............................................................................................................................1
1.1 Solar Cell...................................................................................................................1
1.1.1Semiconductor.......................................................................................................1
1.1.2 P-N Junctions........................................................................................................2
1.2 Electrolyser ...............................................................................................................5
1.2.1 Alkaline water electrolyser...................................................................................5
1.2.2 Proton exchange membrane water elecrolyser......................................................5
1.3 Fuel Cells...................................................................................................................6
2. Experimental Method...................................................................................................8
2.1.1 The Aim Of The Experiment...................................................................................8
2.1.2. Description Of Apparatus.....................................................................................8
2.1.3. Experimental Procedure.........................................................................................8
3. Result And Discussion................................................................................................10
4. Conclusion...................................................................................................................24
5. Nomenclature...............................................................................................................26
6. References......................................................................................................................27
7. Appendices.....................................................................................................................28
7.1Data sheet……………………………………………………………………………..32
SUMMARY
Electrolysers and fuel cells are very important devices whose working principle is reversible
in basic. In Fuel Cell experiment an electrolyser and a fuel cell were studied. A lamp was used
as an energy source.
In the first part of experiment change of current and voltage were recorded for different
distances of energy source to the solar panel. A graph according to current versus voltage was
plotted. Current increased with increasing voltage. It was observed that electrolysis started at
1.453V.
In the second part of the experiment fuel cell was studied. For a circuit either open loop or
closed loop with different resistances, voltage and current values were measured. By these
data power consumption was calculated. Measured voltage values were shown in a graph
versus current. Even the current increased, voltage decreased because of decreasing
resistance. A graph for calculated power values versus current was plotted. Power decreased
with increasing current because of decreasing resistance.
In the third step of experiment efficiency of fuel cell was studied. For open loop, 2 ml H2 was
leaked in 5 min. For closed loop with 3 ohm resistance, 3 ml H2 was leaked in 3 min. By
using these data 1,8 ml lost H2 was calculated. Farraday efficiency was calculated as 0.22 to
see how much H2 was consumed in water production and lost from leaks.
In the fourth part of the experiment two types of connection were studied as fuel cells
connected in series or parallel. In the first step, fuel cell was connected in series. For either
open loop or closed loop with different resistances, voltage and current values were measured.
After recording measured data, the same procedure was done when fuel cell was connected in
parallel. Power consumption was calculated for both steps of experiment. Voltage and power
change according to current was graphed for both steps. In the first step fuel cells are in series,
voltage decreased with increasing current because of decreasing resistance. change according
to current was observed in a graph. Power increased until a peak point of 664.2mW and after
that point decreased. In the second step with fuel cells in parallel, voltage decreases with
increasing current power increases. When a lamp and motor was connected to the circuit in
series and parallel, voltage values were measured and compared with each other. It was
observed that lamp was more bright for series.
1.THEORY
1.1.SOLAR CELLS
Solar cells are devices which convert solar energy directly into electricity. The most common
form of solar cells are based on the photovoltaic effect in which light falling on a two layer
semi-conductor device produces a photovoltage or potential difference between the layers.
This voltage is capable of driving a current through an external circuit and thereby producing
useful work. [1] The basic processes behind the photovoltaic effect are generation of the
charge carriers due to the absorption of photons in the materials that form a junction;
subsequent separation of the photo-generated charge carriers in the junction; and collection of
the photo-generated charge carriers at the terminals of the junction. [2]
1.1.1 SEMICONDUCTOR
Silicon, symbol Si, is the most commonly used basic building block of integrated
circuits. Silicon is intrinsic semiconductor, which means that its electrical behavior is
between that of a conductor and an insulator at room temperature. [3] The important
requirement for the semi-permeable membranes is that they selectively allow only one type of
charge carrier to pass through. [4] Intrinsic silicon must be modified by increasing the number
of free electrons or holes to increase its conductivity. This is done by adding immaturities to
the intrinsic materials. Two types of extrinsic semi conductive materials n-type and p-type
are the key building blocks for most types of electronic devices. To build these semi
conductros there is a method due to which we can get pure semiconductors , this process is
called doping. [5] To increase the number of conduction – band electrons in intrinsic silicon,
pentavalent impurity atoms are aded. These are atoms with five valence electrons such as
arsenic (As), Phosphorus (P) , Bismuth (B) , and Antimony (Sb). Each pentavalent atom
forms covalent bonds with four adjacent silicon atoms. Four of the Phosphorus atoms’s
valence electrons are used to form the covalent bonds with silicon atoms, leaving one extra
electron. This extra electron becomes a conduction electron because ti is not attached to any
atom. Because the pentavalent atom gives up an electron, it is often called a donor atom. The
number of conduction electrons can be carefully controlled by the number of impurity atoms
added to the silicon. A conduction electron created by this doping process does not leave a
hole in the valence band because it is in excess of the number required to fill the valence
band. For P – type semiconductors, the number of holes in intrinsic silicon is increased,
trivalent impurity atoms are added. These are those atoms with three valence electrons such
as Boron (B), indium (in), and gallium (Ga). Each trivalent atom forms covalent bonds with
four adjacent silicon atoms. All three of the boron atom’s valence electrons are used in the
covalent bonds; and, since four electrons are required, a hole results when each trivalent atom
is added. Because the trivalent atom can taken an electron, it is often referred to as an
acceptor tom. The number of holes can be carefully controlled by the number of trivalent
impurity atoms added to the silicon. A hole created by this doping process in not
accompanied by a conduction free electron.
Figure 1.1.1 P and N Type Semiconductors
1.1.2 P-N JUNCTIONS
Highly-doped n-type and p-type membranes, regions are formed with an internal electric
field. These regions are especially important for solar cells and are known as p-n junctions.
Figure 1.2.1 Highly-doped n-type and p-type membranes which are formed with an internal
electric field
When a p-type and an n-type semiconductor are brought together, a very large difference in
electron concentration between n- and p-type semiconductors causes a diffusion current of
electrons from the n-type material across the metallurgical junction into the p-type material.
Figure 1.2.2 Diffusion of currents in p-n junction
The diffusion currents continue to flow until the forces acting on the charge carriers, namely
the concentration gradient and the internal electrical field, compensate each other. The driving
force for the charge transport does not exist any more and no net current flows through the p-n
junction. A depletion region forms instantaneously across a p-n junction. [4]
Figure 1.2.3 Depletion layer of p-n junction
1.2. ELECTROLYSER
The electrolysis of water is considered a well-known principle to produce oxygen and
hydrogen gas. The core of an electrolyser is an electrochemical cell, which is filled with pure
water and has two electrodes connected with an external power supply. At a certain voltage,
which is called critical voltage, between both electrodes, the electrodes start to produce
hydrogen gas at the negatively biased electrode and oxygen gas at the positively biased
electrode. The amount of gases produced per unit time is directly related to the current that
passes through the electrochemical cell. In water, there is always a certain percentage found
as ionic species; H+ and OH- represented by the equilibrium equation:
H2O (l)↔ H+ (aq) + OH- (aq)
Oxygen and hydrogen gas can be generated at noble metal electrodes by the electrolysis of
water:
+ electrode (anode): 4OH- ↔ 2H2O + O2 + 4e-
- electrode (cathode): 2H+ (aq) + 2e-↔ H2 (g)
1.2.1. Alkaline water electrolyser
The principle of alkaline water electrolysis is that Two molecules of water are reduced to one
molecule of hydrogen and two hydroxyl ions at the cathode. The hydrogen escapes from the
surface of the cathode recombined in a gaseous form and the hydroxyl ions migrate under the
influence of the electrical field between cathode and anode through the porous diaphragm to
the anode, where they are discharged to ½ molecule of oxygen and one molecule of water.
The oxygen recombines at the electrode surface and escapes as hydrogen does, as a gas.
1.2.2 Proton exchange membrane water electrolyser
The proton exchange membrane water electrolysis is based on the use of a polymeric proton
exchange membrane as the solid electrolyte (polymer electrolyte membrane). The following
advantages of polymer electrolyte technology over the alkaline one have been proposed: (i)
greater safety and reliability are expected since no caustic electrolyte is circulated in the cell
stack; (ii) previous tests made on bare membranes demonstrated that some materials could
sustain high differential pressure without damage and were efficient in preventing gas mixing;
and (iii) the possibility of operating cells up to several amps per square centimeter with
typical thickness of a few millimeters is theoretically afforded. Ultrapure water is fed to the
anode structure of the electrolysis cell which is made of porous titanium and activated by a
mixed noble metal oxide catalyst. The membrane conducts hydrated protons from the anode
to the cathode side. [6]
1.3 FUEL CELLS
A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has two
electrodes, one positive and one negative, called, respectively, the anode and cathode. The
reactions that produce electricity take place at the electrodes.
Every fuel cell also has an electrolyte, which carries electrically charged particles from one
electrode to the other, and a catalyst, which speeds the reactions at the electrodes.
Hydrogen is the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is
that they generate electricity with hydrogen and oxygen used in generating electricity
ultimately combine to form a harmless byproduct, namely water.
In general, the low temperature fuel cells are better suited to battery replacement in mobile
and portable applications, while the high temperature types are most appropriate for stationary
power and CHP applications where rapid start-up and load-following are less of an issue.
Importantly, the heat generated can be utilised in these applications.
In vehicle applications, PEM fuel cells are of interest because they have fast start capability;
they operate at low temperatures, and have appropriate specific energy densities.
With a limited operating life, the lifecycle costs are high. The operating temperature of below
100°C makes it difficult to extract heat energy for co-generation in CHP applications.
However, some PEMs are being trialled in micro-CHP in Europe and Japan.
On the other hand, zirconia-based SOFCs (CFCL’s technology) are far better positioned for
co-generation given their far longer operating life; furthermore the much higher operating
temperature makes co-generation highly efficient. A further crucial advantage of SOFCs is
that they can run directly on natural gas, propane or other readily available fuels without need
for reforming, while PEM fuel cells must reform and purify those fuels before they can be
used.
DMFCs are a type of PEM technology where methanol is fed directly to the fuel cell. While
less efficient than hydrogen-based PEM, they are compact and have applications for consumer
electronics (ranging from laptops to mobile phones), especially where users are unable to
recharge their batteries for some time. Methanol fuel cells were cleared for use on aircraft in
the autumn of 2007.
AFCs depend on pure oxygen and hydrogen for optimal performance and cannot function in
the presence of carbon dioxide. To date, despite the attractions of this technology – in
particular its high system efficiency – the carbon dioxide issue has limited its applications to
aerospace. However, second, and more recently third, generation AFCs have been produced
which are suitable for domestic and industrial applications.
MCFCs are a relatively low cost fuel cell able to use a broad range of fuel stocks including
coal gas, and have found use in large power generation applications. PAFCs are expensive
and operate at high temperatures: however, they are considered tried and tested, especially for
distributed energy generation.
Table 1.3.1 Different types of fuel cells
2. EXPERIMENTAL METHOD
2.1 The Aim Of The Experiment
The aim of this experiment is to observe the voltage and current changes in different cell
types, calculation of power consumption and efficiency for fuel cell.
1.Description of Apparatus
Solar module
Lamp as a light source
Electrolyser
Fuel Cell
Load Measurement box
Connecting leads
2 long tubes
2 short tubes
2 small test tubes
2 tubing stoppers
And distilled water was used as experimental component.
The listed equipment was used in the experiment. Flow pattern which was seen for every
impeller in the cylindrical mixing vessel was drawn. The experimental data was obtained for
every speed from dynamometer and was recorded in the data sheet for each part of the
experiment.
2)Experimental Procedure
The first part of the experiment was done with electrolysis unit by using lamp. Lamp was put
in 25cm and for every 5 cm closer point to the solar panel, voltage and current data were
taken. In the second part of the experiment lamp was put to the closest point to the system.
For different resistance adjustments voltage and current was recorded for fuel cell. Before
starting to the third part of the experiment purging was done. Hydrogen lost in the system was
observed. Than voltage and current values were measured in every 30 seconds. In the fourth
part of the experiment fuel cells were connected in series and for different resistance
adjustments voltage and current was measused. The fuel cells were connected in paralled and
the same procedure with series connection was done. For lamp and motor in the circuit,
voltage data were taken for series and parallel connections.
3.RESULTS & DISCUSSION
3.1 ELECTROLYSER
The experiment was conducted in three parts. The first part of the experiment's objective is
that by using solar module how the current and voltage change. For this reason, electrolyser
was connected to load measurement box and lamp was turned on. It was placed 25m away
from the system. The displacement was changed during the experiment while current and
voltage values were read. The values were taken at six different placement.
Table 3.1.Characteristics of The Electrolyzer
V(Volt) I(mA) Distance of Light(cm)
1.453 47 25
1.458 58 20
1.465 75 15
1.472 98 10
1.481 134 5
1.492 187 0
Table 3.1 contains the characteristic data of elecrolyser. Distance is a manipulated variable
and it was changed to measure voltage and current values. By this way it would be analyzed
as shown in Figure 3.1. The most striking feature of the Table 3.1 is that when voltage
increases, current increases too if light is made closer.
Figure 3.1.Characteristic Curve of the Electrolyzer
Figure 3.1 shows a relationship about how current is changing while voltage too. Data were
taken at six different point. And it was seen that there is a gradual increase. The lowest
voltage was obtained at 1.453V and it increased until 1.492V. If the light was getting closer to
solar module, it could be more effective on the system. The results show that the interval of
the rise is bigger compare to initial current value. The I / V characteristic curve does not cross
the origin. Electrolysis starts only at 1.453 V. The voltage increases with an increasing
current. Below a voltage of approximately 1.453 V there is no electrolysis taking place, since
the electric potential for the decomposition of water is not sufficient. Electrolysis starts only
when the voltage reaches the practical decomposition voltage of 1.453 V. This voltage is
composed of the individual redox potentials (1.23 V, theoretical decomposition voltage) and
the losses (excess voltage) in the cell. With an increasing current, the losses increase and
therefore the voltage also increases. Chemical (H2) energy is being created, a minimum
energy must be input to drive the process according to the laws of thermodyna- mics. In terms
of electrical energy, this corresponds to a voltage greater than 1.23V. In reality, the working
voltage necessary to sustain water electrolysis is always greater than this. The extra voltage,
generally known as the over voltage, represents a waste of energy or loss of efficiency. It has
two main causes, one of which is the internal voltage drop loss due to the finite electrical
resistance of the electrolyte, or membrane in this case. The second is kinetic in origin, i.e., to
do with the overall speed of the process at the electrode surface.
1.450 1.455 1.460 1.465 1.470 1.475 1.480 1.485 1.490 1.495
0
20
40
60
80
100
120
140
160
180
200
VOLTAGE
CUR
REN
T
3.2.SINGLE FUEL CELL
First of all, the implementation was made as in the Figure 3.2. For this part the energy will be
obtained from Fuel Cell device.
Figure 3.2. Experimental Set-up for single fuel cell
A fuel cell will provide energy so long as hydrogen and oxygen are supplied to it.The current
and voltage output will depend up on the load applied to the fuel cell and can be seen from its
characteristic curve as shown in Figure 3.3. As the processes in a fuel cell are the reverse of
electrolysis it is useful to compare the characteristic curves of the fuel cell and electrolyser .
During the experiment resistance load was altered and for each resistance voltage and current
measurements were taken for 30 seconds for each one. Table 3.2 was obtained in result of
different resistance values. And measuring current and voltage gave the power.
Table 3.2. Measurements with Lamp
Resistance (R)
(Ω)
Voltage(V)
(V)
P(mW) Current(I)
mA
open-loop 0.803 - -
50 0.744 1280 160
10 0.672 372.5 193
3 0.564 160.1 231
1 0.364 68.12 261
0.3 0.123 58.08 440
The load resistances were changed quickly as the amount of gases ( H2 and O2 ) were
decrease very quickly.They were accumulated in the system with electrolyser and Fuel cell
causes this decreasement because it is working in reverse method by this way it consumes
hydrogen and oxygen in order to produce energy.
Table 3.3. Measurements with Lamp to Observe consumption of Hydrogen Gas
Time(s) Voltage(V)
(V)
P(mW) Current(I)
(mA)
30 0.85 1.875 25
60 0.68 1.2 20
90 0.60 0.972 18
120 0.54 0.768 16
150 0.50 0.675 15
180 0.48 0.588 14
Table 3.3 illustrates that measurements were taken in 3ohm for each 30 seconds during the 3
minutes. The initial hydrogen gas was 8ml but at the end it dropped to 5mL. By helping these
two tables Figure 3.3 and Figure 3.4 were drawn as a result of data.
Figure 3.3. Relationship between voltage and current for lamp
In Figure 3.3, while current values are increasing, voltage values are decreasing because
resistance are decreasing too. The highest voltage to success reaction is 0.8V. In the beginning
of the reaction voltage value was 0.8V but it was getting to begin to decrease very sharply,
and then it goes down gradually by 0.1V. However the maximum theoretical value is 1.23V
but unfortunately it could not reached. A single fuel cell can produce at about 0.7-0.8 volts
maximum. Because , intermediate molecules bond too tightly or too loosely to the cathode
surface, slowing the reaction and causing a drop in voltage. The result is the fuel cell produces
about 0.8 volts instead of the potential maximum of 1.23 volts. To eliminate loss , fuel cells
should be stacked together in series to increase the voltage by the number of cells or a catalyst
should have bonding strengths tailored so that all reactions taking place during oxygen
reduction occur at or as near to 1.23 volts as possible.
0 50 100 150 200 250 300 350 400 450 500
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0.900
Lamp
current
volt
age
Figure3.4.Power consumption of Fuel Cell
According to Figure 3.4, power consumption is decreasing while current is increasing over the
experiment. Because resistance is decreasing.Power consumption is decreased to 50mW from
1300mW. Only when a readily measurable current flows, has the water started to split into
hydrogen and oxygen. In our example it occurs at 0.744V. The theoretical decomposition
voltage is 1.23V. Below this no splitting takes place. In practice, however this voltage is
lower. The difference between the theoretical actual value of this voltage depends on several
parameters, e.g. The type and composition of the electrode material, the electrolyte and the
temperature.
3.3. THE EFFICIENCY OF A FUEL CELL
For single fuel cell, 2ml H2 was leaked in 5 minutes. When resistance was stabilized at 3ohm
volume loss of H2 from storage was 3ml in 3 minutes. By using this loss volume amount of
hydrogen which was used for the reaction was calculated as 1.8mL.
Table 3.4.Measurement Data which was during 3 minutes
Time(s) Voltage(V)
(V)
P(mW) Current(I)
(mA)
Energy
Efficiency
30 0.85 1.875 25 0.0297
60 0.68 1.2 20 0.048
90 0.60 0.972 18 0.0625
0 50 100 150 200 250 300 350 400 450 500
0
200
400
600
800
1000
1200
1400
lamp
current
po
we
r co
nsu
mp
tio
n
120 0.54 0.768 16 0.074
150 0.50 0.675 15 0.083
180 0.48 0.588 14 0.0918
Table 3.4 illustrates that measurements were taken in 3ohm for each 30 seconds during the 3
minutes. The initial hydrogen gas volume was 8ml but at the end it dropped to 5mL.Power
consumption and energy efficiency coulumns were obtained by calculating as in the
calculation part. The highest volatge is 0.85V that measured and there is one striking feature
of the table that energy efficiency is rising from 1.17% to 5.5% . On the other hand, Faraday
efficiency was found as 22.2% . One form of efficiency, the Faraday Efficiency, is a
percentage that indicates how much of the hydrogen gas is being used for intended electrical
energy production and how much is lost to other factors, like heat. If the fuel cell was perfect
and all conditions were ideal, the Faraday Efficiency would be equal to “1” or 100%. But, this
conditions were not perfect as 22.2% efficiency was obtained from the experiment. To
improve efficiency membrane would be change, surface area would be extended to contact
efficiently.By using Table 3.4 power and efficiency values were graphed into Figure 3.5 in the
below.
Figure 3.5. Power – Efficiency curve of hydrogen fuel cell
0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000
0.000
1.000
2.000
3.000
4.000
5.000
6.000
7.000
8.000
9.000
10.000
power
en
erg
y e
ffic
ien
cy %
When taking into consideration the Figure 3.5, with the hydrogen fuel cell , high efficiency
can be obtained by using low voltage values and low current. For this reason it cause low
energy consumption. By this way with the hydrogen fuel cell as consuming less energy much
efficiency can be achieved. n. Fuel cell systems must be cost compe- titive with, and perform
as well or better than, traditional power technologies over the life of the system.Hydrogen fuel
cells, which use electric motors, are much more energy efficient and use 40-60% of the fuel’s
energy — corresponding to more than a 50% reduction in fuel consumption.
3.4.1.FUEL CELL IN SERIES
Figure 3.6. Schematic Diagram for Fuel Cells Connected in Series
This time , the aim of the experiment is to investigate the behavior of fuel cells connected in
series and parallel. In the third part of the experiment, hydrogen fuel cells were connected in
series as shown in the Figure3.6. Energy was produced from series -connected fuel cells.
Again resistances were changed to acquire voltage and current values. After measuring these
values, power consumption was calculated and Table 3.5 was made up.
Table 3.5 Characteristics of Fuel Cells In Series
Fuel cells in series Single fuel cell theoretical Single fuel cell
experimental
R(ohm) V(volt) I(mA) P(mW) V(volt) I(mA) P(mW) V(volt) I(mA) P(mW)
open 1.729 - - 0.864 - - 0.803 - -
50 1.561 33 54.45 0.781 33 25.77 0.744 160 1280
10 1.430 137 187.69 0.715 137 97.96 0.672 193 372.5
3 1.320 359 386.6 0.660 359 236.9 0.564 231 160.1
1 0.940 815 664.2 0.470 815 383.1 0.364 261 68.12
0.3 0.633 930 259.47 0.317 930 294.8 0.123 440 58.08
Table 3.5 consists of three section.The first section is about measurement with ser-connected
fuel cells. The second one is single fuel cell theoretical values were found according to fuel
sell in series. The voltage values are half of it because resistances are the same and current
equals to total one so, from ohms law of equation voltages must be dropped to half values.
When looking at single fuel cell experimental values they were obtained from the data which
were taken at the beginning of the experiment. By using Table 3.5 values, Figure 3.7 and 3.8
were drawn.
Figure 3.7. Relationship between current and voltage for fuel cells which is connected in
series
Figure 3.7 shows a relationship between current and voltages.While current increases, the
voltage decreases. The reason of this is finding the change of voltage values according to
current values cause energy is produces in fuel cells In series, the lamp and motor voltage was
measured as 1.444 V and 1.501V respectively. From Ohm’s Law it can be seen that internal
resistance of the motor is bigger than the lamp. Only when a readily measurable current flows,
has the water started to split into hydrogen and oxygen. In our example it occurs at 1.561V.
The theoretical decomposition voltage is 1.23V. Below this no splitting takes place. In
practice, however this voltage is higher because of overvoltage. The difference between the
theoretical actual value of this voltage depends on several parameters, e.g. The type and
composition of the electrode material, the electrolyte and the temperature. Adding more cells
in series to increase stack voltage is relatively straightforward, but the reliability of each cell-
to-cell connection becomes more critical since the overall reliability of a stack of N cells is a
function of the reliability of each connection raised to the Nth power. Also, the resistive losses
at the cell-to-cell junctures increase with each connection, and the proportion of system
volume required for manifolding of the inlet and return gases increases.
0 100 200 300 400 500 600 700 800 900 1000
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
1.600
1.800
2.000
fuel cell in series
lamp
motor
current
volt
age
Figure 3.8. Relationship between current and power for fuel cells which is connected in series
Figure 3.8 is the characteristic curve of fuel cell connected in series. Unlike Figure 3.4 ,
power consumption is increasing with current up to a peak point of 664.2mW, and from this
point there is a dramatic drop by approximately 270mW. It consumes power so much at
higher current values.
The power output decreases with increasing load resistance, but fuel efficiency increases.
Power delivered by the fuel cell is maximized when the external load matches the internal
resistan- ce of the fuel cell system.
3.4.2.FUEL CELL IN PARALLEL
In this part of the experiment, the fuel cells were connected in parallel way as shown in the
Figure3.9 in below. This time energy was produced by parallel -connected fuel cell. Current
and voltage values were measured by changing resistance values. Resistance was changed in
order to see relationship between current and voltage.
0 100 200 300 400 500 600 700 800 900 1000
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
fuel cells in series
current
po
we
r
Figure 3.9 Schematic Diagram for Fuel Cells Connected in Parallel
Table 3.6 consists of ten columns that related with measured and calculated values of parallel
fuel cell, single fuel cell theoretical and single fuel cell experimental.
Table 3.6 Characteristics of Fuel Cells In Parallel
Fuel cells in parallel Single fuel cell theoretical Single fuel cell
experimental
R(ohm) V(volt) I(mA) P(mW) V(volt) I(mA) P(mW) V(volt) I(mA) P(mW)
open 0.862 - - 0.862 - - 0.803 - -
50 0.834 18 15.01 0.834 9 7.506 0.744 160 1280
10 0.779 76 59.2 0.779 38 29.60 0.672 193 372.5
3 0.754 211 159.1 0.754 105.5 79.55 0.564 231 160.1
1 0.652 570 371.6 0.652 285 185.8 0.364 261 68.12
0.3 0.536 1154 618.5 0.536 577 309.3 0.123 440 58.08
The first two columns were measured during the experiment. Single fuel cell theoretical
values were calculated accordance with ohm law of equation. According to that law, for
parallel connected fuel cell, specific current value must be half of the total current and voltage
values must be equal to one fuel cell. By using Table 3.6 data, Figure 3.9 and Figure 3.10
were drawn.
Figure 3.10. Relationship between current and voltage for fuel cells which is connected in
parallel
As shown in the Figure 3.10 voltage value for the motor was 0,802 V and for the lamb was
0,769V Ohm’s Law infers that resistance of lamp is bigger than the motor. This leads to
motor consumes more energy. When comparing with Figure 3.7 and Figure 3.3, it is evidently
shown that voltage decreases while current value was obtained in parallel connected fuel cell
current increases but there is a difference between them , in the same resistances the highest
because resistance is dropped half value.(Ohm law).
0 200 400 600 800 1000 1200 1400
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0.900
1.000
lamp
motor
parallel-connected fuel cell
current
volt
age
Figure 3.11. Relationship between current and power for fuel cells which is connected in
parallel
In Figure 3.11 there is a gradual increase of power accordance with current. While current
increases, power consumption increases too.
0 200 400 600 800 1000 1200 1400
0
100
200
300
400
500
600
700
lamp
current
po
we
r
4.CONCLUSION
In the “ Fuel Cell” experiment five different experiments were made. For these experiments
electrolyser, solar module, hydrogen fuel cell, load measurement box and lamp were used.
The first part of the experiment has an objective that learning working principle of
electrolyserand solar module. By using desk lamp and hydrogen and oxygen generated
photovoltaically it wasinvestigated how the current also voltage changes with the difference
between solar module and lamp. The measurements were taken for six different distance. The
minimum voltage was found as 1.453V to begin electrolyse process. However, the theoretical
value is 1.23V and it could not possible to reach this value. The working voltage necessary to
sustain water electrolysis is always greater than this. Generally speaking, extra voltage shows
the waste of energy or loss of efficiency.The reasons could be shown as the internal voltage
drop loss due to the finite electrical resistance of the electrolyte, or membrane in this case and
kinetic in origin.In addition, Faraday Efficiency was calculated as 22.2% . If the system works
successfully and all the conditions are perfect, Faraday Efficiency would possibly be 100%.
But as extra voltage shows that there is a loss of efficiency. To eliminate this problem, the
surface area should increased or itshould be less thick.
In the second part of the experiment fuel cell was used. The main objective was that by using
hydrogen and oxygen generated photovoltaically to investigate how the current produced by
the cell varies with the voltage. At six different resistance values, voltage and current
measured. Also there is an important point that these measurements were taken as soon as
possible otherwise the storaged hydrogen gas would be consumed without taking any data.
The necessary voltage value found as 0.744V to begin reaction. However, the maximum
theoretical voltage is 1.23 and the maximum experimental is 0.803V. The experimental value
is again less than theoretical one as waste of energy or loss of efficiency or internal resistance
of lamp or thickness of membrane that leads to obtain less efficient diffusion of ions. Also,
the difference between the theoretical actual value of this voltage depends on several
parameters, e.g. The type and composition of the electrode material, the electrolyte and the
temperature.
On the other hand, hydrogen gas volume was measured to access the entering volume to
reaction.For single fuel cell, 2ml H2 was leaked in 5 minutes. When resistance was stabilized
at 3ohm volume loss of H2 from storage was 3ml in 3 minutes. By using this loss volume
amount of hydrogen which was used for the reaction was calculated as 1.8mL. And from there
energy efficiency was calculated as 9.18%.
In the last part of the experiment, behavior of fuel cells connected in series and parallel were
investigated. The fuel cells connected in series and parallels to increase the voltage by the
number of cells . When fuel cells were connected in series the maximum voltage was obtained
as 1.729V for starting to reaction. The same pattern was observed in parallel connected fuel
cells which is obtained as 0.834V to begin reaction. Moreover , in the third part of the
experiment motor was used too. Their voltages were measured as 1.444V for lamp and
1.501V for motor in series. In parallel one these values are 0.769V and 0.802V respectively.
As a result , larger voltages were obtained by connecting two cells in series. Characteristics
curve of electrolyser and fuel cell were analyzed as characteristic efficiency curves for all part
of the experiment. Faraday and energy efficiency was calculated very low for this system . To
improve efficiency membrane would be changed with more powerful light source or surface
area would be extended to contact efficiently.
5.NOMENCLATURE
D: Distance (Centimeter ,cm)
I : Current (Ampere ,A)
R: Resistance (Ohm ,Ω)
V: Voltage (Volt, V)
6) REFERENCES
[1]http://www.esdalcollege.nl/eos/vakken/na/zonnecel.htm
[2] P. Würfel, Physics of Solar Cells: From Principles to New Concepts, Wiley-WCH,
Weinheim, 2005
[3] http://www.siliconfareast.com/semicon_matls.htm,
[4]http://ocw.tudelft.nl/fileadmin/ocw/courses/SolarCells/res00028/CH4_Solar_cell_operatio
nal_principles.pdf
[5] http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html
[6]http://www.cres.gr/kape/publications/papers/dimosieyseis/ydrogen/A%20REVIEW%20O
N%20WATER%20ELECTROLYSIS.pdf
[7]http://www.cleantechinvestor.com/portal/fuel-cells/6426-the-main-types-of-fuel-cell-
technology.html