- #1
clementlee87
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Hi, I'm working on a commercially available PEM fuel cell and I'm trying to calculate the theoretical voltage of the cell:
The only electrochemical reaction considered is H2 + 0.5O2 --> H2O
And I understand that I need to use the Nernst equation:
E = EO - (RT / 2F) ln (PH2O / (PH2 * SQRT(PO2))
The anode side in is pure hydrogen from a gas canister at 300 ml/min at 5 psi
The cathode side in is air from ambient at 1 atm
The operating temperature is 50 C, or 323 K.
How can I determine the partial pressure of water produced? If I assume that the water produced is at the vapor pressure of water at my room conditions, it should be at approximately 1584.9 Pa (50% RH at 28 C).
And if I used these pressures,
P H2O = 1584.9 Pa
P H2 = 34483 Pa
P O2 = 21287 Pa
I would get ln (PH2O / (PH2 * SQRT(PO2) = -8.063. This in turn gives me 0.112 V. For this 12 fuel cell stack, that would be equal to 1.344 V. However, the produced voltage when measured with a handheld ammeter reads about 7.2 V.
So wouldn't that mean my efficiency is more than 100%?
Thanks for your help! I need it as soon as I can.
The only electrochemical reaction considered is H2 + 0.5O2 --> H2O
And I understand that I need to use the Nernst equation:
E = EO - (RT / 2F) ln (PH2O / (PH2 * SQRT(PO2))
The anode side in is pure hydrogen from a gas canister at 300 ml/min at 5 psi
The cathode side in is air from ambient at 1 atm
The operating temperature is 50 C, or 323 K.
How can I determine the partial pressure of water produced? If I assume that the water produced is at the vapor pressure of water at my room conditions, it should be at approximately 1584.9 Pa (50% RH at 28 C).
And if I used these pressures,
P H2O = 1584.9 Pa
P H2 = 34483 Pa
P O2 = 21287 Pa
I would get ln (PH2O / (PH2 * SQRT(PO2) = -8.063. This in turn gives me 0.112 V. For this 12 fuel cell stack, that would be equal to 1.344 V. However, the produced voltage when measured with a handheld ammeter reads about 7.2 V.
So wouldn't that mean my efficiency is more than 100%?
Thanks for your help! I need it as soon as I can.