Fuel Cell External Circuit

The cell generates a voltage and provides a current to the external circuit. The voltage that can be supplied depends upon the current drawn.

The voltage, E, of the "ideal" cell is related to the energy available in the reaction, dG, and the number of electrons released per molecule:
E = -dG/n_eF
where dG is the Gibbs function change in the reaction, n_e is the number of electrons, and F is the Faraday constant.

For the cell reaction: dG = - 56,690 cal/g mole of H₂, n_e = 2, and F = 96,500 C/g mole
Substituting these values gives an ideal cell voltage of: E = 1.229 volts