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UNIVERSITY OF MINNESOTA DULUTHDEPARTMENT OF CHEMICAL ENGINEERING

ChE 3211-4211

CHARACTERISTICS OF A FUEL CELL

OBJECTIVE

The purpose of this experiment is to explore the characteristics of a polymer electrolytemembrane (PEM) fuel cell. The relationship of voltage to current or current density is called thecharacteristic curve. The effect of gas quality entering the fuel cell will also be explored to findthe effects on the characteristic curve along with the Faraday efficiency of the cell.

INTRODUCTION

The first fuel cell was built in 1839 by Sir William Grove, a Welsh judge and gentlemanscientist. It was thought that if water was separated into hydrogen and oxygen gas whenelectricity was passed through it, the reverse had to be possible. That was accomplished. Unfortunately the application of a fuel cell as a power source was not utilized until the 1960's foruse in the space program, making fuel cells a relatively young technology. Today fuel cells arebeing explored as a viable replacement to burning fossil fuels. Fuel cells can be used to powerautomobiles, heat and power homes and even replace watch batteries.

The basic concept of the fuel cell is that hydrogen fuel is fed into the “anode” of the fuelcell. Oxygen (or air) enters the fuel cell through the cathode. Encouraged by a catalyst, thehydrogen atom splits into a proton and an electron, which take different paths to the cathode. The proton passes through the electrolyte. The electrons create a current that can be utilized topower a motor before they return to the cathode to be reunited with the hydrogen and oxygen toproduce water.

Proton Exchange Membrane (PEM) cells operate at relatively low temperatures (about 175degrees F or 80 degrees C), have high power density, can vary their output quickly to meet shiftsin power demand, and are suited for applications, -- such as in automobiles -- where quickstartup is required. Figure 1. is a basic diagram of how a PEM fuel cell operates.

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EQUIPMENT

1. Solar Panel and test leads with banana plugs2. Electrolyzer ECO3. H2/O2 and H2/Air Fuel Cells4. Wire leads with banana plugs5. Stopwatch6. VOM meters7. Resistance box8. Ruler 6 or 12 inch9. Calipers

CHEMICALS/MATERIALS

1. Deionized water

Figure 1. Diagram of how a basic polymer electrolyte fuel cell works.

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EQUIPMENT SET UP

Electrolyzer Eco

The use of PEM electrolyzers is growing with the increased use of fuel cells. Electrolyzersare an environmental friendly means of producing from water, the hydrogen necessary to operatefuel cells. The electrical energy needed can be obtained from a number of renewable sources,such as solar cells, wind or hydroelectric power.

The electrical energy splits the water in the electrolyzer according to the equation . This process takes place in the membrane electrode assembly (MEA). 2 22 2 2H O H O→ +

The MEA consists of a cathode, an anode and a special polymer membrane (PEM), which allowsprotons to pass through but represents a barrier for electrons.

Figure 2. shows the Electrolyzer Eco (right side of figure) set up for operation. Theadditional Figures provide a visual supplement to the operating instructions.

Figure 2. Diagram of the Electrolyzer Eco (right Side).

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Electrolyzer Operating Instructions

1. Connect the gas lines (silicone tubing) to thestorage tank outlets.

2. Close the tubing clamp (A)

3. Fill the storage tanks up to the gas outlet tubingconnections with deionized water.

4. Squeeze the top silicone tubes of the electrolyzerrhythmically between thumb and forefinger toexpel the air from the lines (B). NOTE: Normallyit is not necessary to do this step.

5. Top off with deionized water to fill the storagetanks to the top.

6. Mount the compensation tanks (C) on the storagetanks. Some water may overflow - wipe up.

7. Connect the solar panel to the electrolyzer.Connect the positive (red) and negative (black)terminals of the solar panel to the positive (red)and negative (black) terminals of the electrolyzerusing red and black test leads with banana plugs.

8. The current splits the water into 1 part of oxygento 2 parts of hydrogen by volume, which arecollected in the gas storage tanks (D).

9. Generate 35 to 40 cm3 of hydrogen beforeconnecting to the Fuel Cell.

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Table 1. Electrolyzer Eco Technical Data

Description Technical Data

Item No. 1939

Height x width x depth 200 x 180 x 120 mm

Weight 500 gm

Electrode Area 16 cm2

Power 2 W

Permissible Voltage 0 - 2.0 VDC

Permissible current 0 - 3 ADC

Gas production (H2/O2) 8.6/4.3 cm3/min

Gas Storage Tank Volume 40 cm3 each

Hydro-GeniusTM School Fuel Cell

Hydrogen gas is oxidized within a fuel cell. In the process, the chemical energy stored inthe hydrogen gas is converted directly, i.e. without combustion, to electrical energy. This processtakes place in the heart of the fuel cell, the membrane electrode assembly (MEA)

Two electrodes (cathode: oxygen side and anode: hydrogen side) and the proton exchangemembrane (PEM) comprise the MEA. The PEM is a special plastic film which is permeable toprotons but presents a barrier to electrons.

Hydrogen gas is split by catalysis into electronsand protons in the fuel cell. Due to the chemicalimbalance, the protons (cations) diffuse throughthe PEM. The resulting potential difference can betapped on the electrodes in the form of a no-loadvoltage. As soon as an electric circuit is connectedto the fuel cell, the surplus electrons flow to thecathode, where they combine with the oxygen andthe protons to form water (H20). Figure 3. shows the Hydro-GeniusTM SchoolFuel Cell set up for operation. The additionalfigures provide a visual supplement to theoperating instructions.

Figure 3. Fuel Cell

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Fuel Cell Operating Instructions

1. Read the General Safety Instructions in theSafety Notes.

2. Open the clamp on the bottom connection(vent) on each side of the fuel cell.

3. Moisten the membrane of the fuel cell byintroducing a small amount of deionized water (one to two drops) through the topconnections on both sides of the cell.

4. Close the clamps on the lower hoseconnections.

5. Open the clamp on the hose from thehydrogen storage tank on the elctrolyzer topurge any water out of the hose. Close theclamp.

6. Open the clamp on the hose from theoxygen storage tank on the electrolyzer topurge any water out of the hose. Close theclamp.

7. Attach the hose from the hydrogen storagetank on the electrolyzer to the topconnection of the fuel cell on the hydrogen,negative (black) terminal side. Open theclamp on this hose.

8. Attach the hose from the oxygen storagetank on the electrolyzer to the topconnection of the fuel cell on the oxygen,positive (red) terminal side. Open theclamp on this hose.

9. Connect an electrical load (resistance box)to the positive (‘+’:red) terminal and thenegative (‘-’:black) terminal of the fuelcell.

10. Open the clamp on the lower hose connection on the hydrogen side and purge the air and

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any extra water out of the fuel cell. Normally use 30 to 35 cm3. If there is not enoughhydrogen in the storage tank, produce additional gas before purging the fuel cell. Closethe clamp.

11. Open the clamp on the lower hose connection on the oxygen side and purge the air andany extra water out of the fuel cell. Normally use 10 to 15 cm3. If there is not enoughoxygen in the storage tank, produce additional gas before purging the fuel cell. Close theclamp

12. Sufficient hydrogen and oxygen have to be purged to yield a maximum voltage readingon the resistance box. If the readings on the resistance box drift, it indicates all the airand water has not been purged from the lines and fuel cell. Additional oxygen andhydrogen will have to be purged through the system. Additional hydrogen and oxygenwill normally have to be generated before the second purging can be done. Additionalgas will have to be generated after the system is purged so you will have sufficient gas torun the experiment.

13. If the readings on the resistance box still drift quite a bit, clamp off the upper hoses at thestorage tanks. Remove the upper hoses at the connectors. Open the clamps on the lowerhoses. Use a squeeze bulb on the upper hose to force additional water out of the fuel cell.Reconnect the upper hoses, close the clamps on the lower hoses, open the clamps at thestorage tanks and purge the system with hydrogen and oxygen. This should helpdecrease the amount of drift. There will always be a small amount of drift.

Table 2. Hydro-geniustm School Fuel Cell Technical Data

Description Technical Data

Dimensions (length x width xheight)

160 mm x 130 mm x 90 mm

Voltage 0.4 - 1.0 V

Current maximum - 2000 mA

Hydrogen Consumption maximum - 15 mL/min at a current of 2000 mA

Electrode Area 16 cm2

Inside diameter of O2 and H2connectors on the fuel cell

3 mm

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Ancillary Equipment - Solar Panel and Resistance Box

Solar Panel - Solar2

The Solar2 is a bank of 3 solar modulesmounted at an angle to capture the energy fromsunlight or a spotlight (when operating indoors). The Solar2 is capable of providing the energynecessary to operate the electrolyzer. A picture isshown in Figure 4.

Operating Instructions

1. Connect the red test lead with the bananaplugs from the red terminal on the solarpanel to the red terminal on the electrolyzer.

2. Connect the black test lead with the bananaplugs from the black terminal on the solarpanel to the black terminal on theelectrolyzer

3. Position the spotlight so the light source is ata minimum of 50 cm from the solar panel.

4. Turn on the spotlight and start producing hydrogen and oxygen with the electrolyzer.

Table 3. Solar Panel Technical Data

Description Technical Data

Dimensions (length x width xheight)

285mm x 150 mm x 70 mm

Output 2.5 V

Current 900 mA

Resistance Box

To provide data that can be used to calculate and plot your characteristic curve using oxygenor air and determine the Faraday efficiency of the system a resistance box is used. Theresistance box contains a series of different size resistors that can be switched into the circuit.

Figure 4. Solar Panel

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Two VOM meters are connected to the resistance box. One to give you voltage (V) data and theother to give you current (Amp) data under different loads.

Operating Instructions

1. Connect a red test lead to the red terminalon the fuel cell and to the red terminal onthe left side of the resistance box. Connecta black test lead to the black terminal onthe fuel cell and to the black terminal onthe left side of the resistance box..

2. Connect a set of red and black test leads tothe red and black terminals on the right sideof the resistance box above the letter “V”. Connect the other end of the black lead intothe terminal labeled “COM” on one of theVOM meters. Connect the other end of the red lead into the terminal labeled “V/Ω” onthe same VOM meter. Set the range switch to 2 DCV.

3. Connect a set of red and black test leads to the red and black terminals on the right sideof the resistance box above the letter “A”. Connect the other end of the black lead intothe terminal labeled “COM” on the other VOM meter. Connect the other end of the redlead into the terminal labeled “A” on the same VOM meter. Set the range switch to 2DCA.

EXPERIMENTAL PROCEDURE

Characteristic Curve

1. After setting up the equipment as described above you are ready to record data.

2. Insure you have produced sufficient gas (hydrogen and oxygen) to run the experiment.

3. Move the resistor switch to place a resistor (100 ohm) in the system. Wait for the meterreadings to stop drifting. This may take a few minutes (there may still be a slow, slowdrift downward which should not hurt your readings). If the meters continue to driftexcessively or if they start to drift faster, it may indicate that you have not purged all theair or water out of the system. You will again have to open the clamps on the lowerhoses on both sides of the fuel cell to purge each side of the cell with its gas, eitherhydrogen or oxygen. After the readings have stabilized, record them.

Figure 5. Resistance box

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4. Move the switch to a lower resistance value, wait at least 30 seconds or until the readinghas stabilized and record the amp and voltage values. Continue until you have movedthrough all the resistance values, recording the data. Do not use a resistance of 3.3 amps. This could cause problems for the fuel cell.

5. Repeat steps 3 & 4 at least two more times so you can conduct an error analysis on thedata.

6. With the data collected, calculate and plot the characteristic curve

Effect of Gas Quality on the Characteristic Curve - Experiment 1.

1. If you do not have enough gas in the storage tanks, produce more gas before conductingthis experiment.

2. Close the clamp on the tubing from the oxygen storage tank. Disconnect the tubing fromthe upper connection on the oxygen side of the fuel cell.

3. Close the clamp on the tubing from the hydrogen storage tank. Disconnect the tubingfrom the upper connection on the hydrogen side of the fuel cell.

4. Using a caliper measure the inner diameter of the tubing connector on the oxygen side ofthe fuel cell (to calculate the area the air passes through).

5. Open the clamp on the lower connection tubing on the oxygen side of the fuel cell. Using a pipette bulb push some air through the upper connection on the oxygen side ofthe fuel cell. This purges the pure O2 out of the system. NOTE: Do not use a lot ofpressure when doing this or you can damage the fuel cell.

6. Close the clamp on the lower connection tubing on the oxygen side of the fuel cell.

7. The oxygen side of the fuel cell should now contain only air.

8. Connect the tubing from the hydrogen storage tank to the upper connection on thehydrogen side of the fuel cell. Open the tubing clamp.

9. Open the clamp on the bottom connector tubing on the hydrogen side and purge the airout of the hydrogen tubing and fuel cell. After purging, close the clamp.

10. Follow steps 3 through 6 found under the instructions for the Characteristic curve above.

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Effect of Gas Quality on the Characteristic Curve - Experiment 2.

1. If you do not have enough gas in the storage tanks, produce more gas before conductingthis experiment.

2. Close the clamps on the hydrogen andoxygen supply tubing coming from theelectroylzer storage tanks.

3. Disconnect both the hydrogen and oxygentubing from the H2/O2 fuel cell.

4. Find the Eco H2/Air fuel cell (has slottedopenings on the O2/Air side). See Figureon the right.

5. Use a calipers to measure the width andlength of the slots so you can calculate thearea the air passes through.

6. Connect the hydrogen tubing from the electrolyzer storage tank to the hydrogenconnector on the fuel cell.

7. Open the clamp on the hydrogen tubing.

8. Open the clamp on the tubing attached to the lower connector to purge air out of thetubing and the fuel cell. After purging, close the clamp.

9. Follow steps 3 through 6 found under the instructions for the Characteristic curve above.

Table 4. Eco H2/Air Fuel Cell Technical Data

Description Technical Data

Dimensions (length x width xheight)

150 mm x 130 mm x 105 mm

Generated Voltage 0.4 - 0.96 V

Power 300 mV

Electrode Area 16 cm2

Area of each slot 144.6 mm2

Number of slots 5

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Faraday Efficiency

1. Record the temperature and barometric pressure in the lab.

2. Produce 20 to 30 cm3 of hydrogen.

3. Connect the hydrogen and oxygen tubes from the electrolyzer storage tanks to the upperconnectors on the hydrogen and oxygen sides of the Hydro-GeniusTM School Fuel Cell. Open the clamps on these tubes.

4. One at a time, open the clamps on the tubing on the lower connectors to purge thehydrogen and oxygen tubing and the fuel cell of water and air.

5. Start the electrolyzer, if not already running, to produce 40 cm3 of hydrogen.

6. Turn off the light to the solar panel so no gas is produced. The test leads can also bedisconnected from the electrolyzer.

7. Set the load switch on the resistance box to a resistance of 10 or 15 ohms. Enough powerat this resistance will be drawn so a measurable amount of gas will be consumed in arelatively short amount of time.

8. Record the volume of hydrogen and the voltage and amp data at two minute intervals.Record this data for the time it takes for the fuel cell to consume 20 cm3 of hydrogen. You will have to estimate the volume used between marks on the tank or use the plasticruler supplied You can also arbitrarily set another volume that will be consumed ratherthan 20 cm3.

9. Repeat this procedure at the same resistance for another one to two times.

10. Also repeat this procedure at one or two different resistances (between 30 and 60 ohm) inorder to compare the Faraday Efficiency at different loads.

If time permits:

Close the clamps on the hydrogen and oxygen tubing from the electrolyzer storage tanks,remove the tubing from the H2/O2 fuel cell, connect the hydogen tubing to the H2/Air fuel celland follow the procedure above to collect data so you can calculate the Faraday Efficiency usingair as the supply of oxygen.

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SAFETY NOTES

1. The hydrogen (H2) and oxygen (O2) produced represent a source of danger if handledimproperly. In order to avoid any risks you must follow the following General safetyPrecautions when working with the electrolyzer and fuel cell.

a. Read the operating instructions above before setting up the electrolyzer - seeabove.

b. Wear safety glasses with side shields or goggles.c. Do not short-circuit or reverse the polarity of the terminals.d. Remove flammable gases, vapors and liquids from the vicinity of fuel cells and

electrolyzers. The catalysts contained in the system can trigger spontaneouscombustion.

e. Hydrogen and oxygen may escape from the system. To prevent the gasescollecting and forming explosive mixtures only use the system in well-ventilatedrooms.

f. Remove from the vicinity of the system any ignition sources (open flame, anymaterials that can be charged with static electricity or substances with a catalyticaction)

g. Hoses, plugs and tanks are used for pressure compensation. Do not fix or securewith clamps, adhesives, etc.

h. Use only the gas storage tanks supplied with the system to store the gas.i. Operate the system at room temperature and ambient pressure.j. Do not position any solar modules and lights in use closer than the permitted

distance (50 cm between the spotlight and the solar modules, one (1) meterbetween the spotlight and the fuel cell).

k. The surface of the spotlight and the solar modules can get very hot during the operation of the experiment.

2. Use safety glasses with side shields while running this experiment.3. Review the MSDSs for hydrogen and oxygen. Hydrogen is an explosive gas. Oxygen

is an oxidizing agent and vigorously accelerates combustion. Contact of oxygen withflammable materials may result in fire or an explosion.

WASTE DISPOSAL PROCEDURES

1. Only water is used in this experiment. There is no hazardous waste to dispose of.

12/09

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Department of Chemical EngineeringStockroom Checkout slip

Fuel Cell Experiment ChE 4211

Name: Date: (print name)

Lab No.: Lab 1 Tuesday 12:00 - 4:50 PM Lab 2: Thursday 12:00 - 4:50 PM

Lab No.: Lab 3 Tuesday and Thursday morning (9:30 - 11:50 AM) (circle one)

Equipment Out In Equipment Out In

Stop Watch 2 - Test leads (Red - Bananaplug on both ends)

2 - Test leads (black - Bananaplug on each end) Caliper

6 in plastic level

Name: (Signature)