1. CHEM 3310
Fuel Cell

2. DG = - nFE DGo = - nFEo Change in Gibbs Free Energy, G
G is the free energy that is available to do useful work such as electrochemical work.
DG = - nFE DGo = - nFEo
An electrochemical cell is able do work if its cell potential, E, is positive.
DG < 0
where n is the number of moles of electrons that flow in the cell, F is Faraday’s constant, coulombs / mole of electrons,
Eo is the standard voltage measured of the electrochemical cell.
CHEM 3310

3. DGo = - nFEo Change in Gibbs Free Energy, G
G is the free energy that is available to do useful work such as electrochemical work.
An electrochemical cell is able do work if its cell potential, Eo, is positive.
DGo < 0
DGo = - nFEo
where n is the number of moles of electrons that flow in the cell, F is Faraday’s constant, coulombs / mole of electrons,
Eo is the standard voltage measured of the electrochemical cell.
CHEM 3310

4. Example: Hydrogen fuel cell
Use solar energy
to break apart water
to generate H2 and O2 as fuel for the fuel cell.
Solar panel
Electrolyzer
Hydrogen Fuel cell
Load box
CHEM 3310

5. Example: Hydrogen fuel cell
Electrolyzer
Hydrogen Fuel cell
Solar panel
Load box
Eo=1.23 V
Anode: H2 (g)  4H+ (g) + 4 e-
Cathode: O2 (g) + 4 H+ (g) + 4 e-  2 H2O (l)
2 H2 (g) + O2 (g)  2 H2O (l) Eo = 1.23 V
CHEM 3310

6. Theoretical decomposition voltage of water
Part A: The Electrolyzer
2 H2O (l)  O2 (g) + 2 H2 (g) E° = V
O2 (g)
H2 (g)
In practice, the external voltage applied to split water always exceeds 1.23 V.
The difference between the theoretical decomposition voltage and the actual
decomposition voltage is called overpotential or overvoltage.
CHEM 3310

7. Part A: The Electrolyzer
2 H2O (l)  O2 (g) + 2 H2 (g) E° = V
Adjust the power supply to obtain, roughly, the following current readings:
0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45 A
CHEM 3310

8. Part A: The Electrolyzer
2 H2O (l)  O2 (g) + 2 H2 (g) E = V
NOTE:
Do NOT let the current
Exceed
0.5 Amp!
Will damage
the electrolyzer
Overpotential = V – 1.23
CHEM 3310

9. Measure the Volume of H2 (experimental) produced in
Part B: The Faraday Efficiency of the Electrolyzer
Measure the Volume of H2 (experimental) produced in
approximately 180 s.
CHEM 3310

10. Part B: The Faraday Efficiency, ŋ, of the Electrolyzer
2 moles of electrons per mole of H2O
Cathode: 4H+ (g) + 4 e-  2H2 (g)
Anode: 2 H2O (l)  O2 (g) + 4 H+ (g) + 4 e-
2 H2O (l)  O2 (g) + 2 H2 (g) E = V .
One mole of electrons has a charge equal to coulombs.
At 20oC, the molar volume of H2 (g) is mL.
Determine ŋ for the each of the two currents.
In commercial electrolyzers, the Faraday efficiency must be close to 1 (i.e. 100%).
CHEM 3310

11. Part C - The Characteristic Curve of the Hydrogen Fuel Cell
2H2 (g)  4H+ (g) + 4 e-
O2 (g) + 4 H+ (g) + 4 e-  2 H2O (l)
NafionTM PEM
Two platinum coated carbon electrodes
bonded to a Proton Exchange Membrane (PEM)
CHEM 3310

12. Part C - The Characteristic Curve of the Hydrogen Fuel Cell
2H2 (g)  4H+ (g) + 4 e-
O2 (g) + 4 H+ (g) + 4 e-  2 H2O (l)
CHEM 3310

13. Part C - The Characteristic Curve of the Hydrogen Fuel Cell
Record the voltage and current of the cell when the cell is subjected to following loads:
200 , 100 , 50 , 10 , 5 , 3 , and 1 ; Lamp; Motor
CHEM 3310

14. Part C - The Characteristic Curve of the Hydrogen Fuel Cell
Record the voltage and current of the cell when the cell is subjected to following loads:
200 , 100 , 50 , 10 , 5 , 3 , and 1 ; Lamp; Motor
CHEM 3310

15. Part C - The Characteristic Curve of the Hydrogen Fuel Cell
Power = Voltage  Current
CHEM 3310

16. Other fuel cell: Methanol fuel cell
Anode:
CH3OH(l) + H2O(l)  CO2(g) + 6 H+ (g) + 6 e-
Cathode:
O2(g) + 4 H+(g) + 4 e-  2 H2O(l)
Overall cell reaction:
CH3OH(l) O2(g)  CO2(g) + 2 H2O(l)
E° = 1.21 V
At the anode methanol is supplied.
At the cathode, oxygen from air is fed in.
CHEM 3310

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CHEM 3310

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CHEM 3310

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CHEM 3310