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