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The chemical thermodynamics of SOFCs

The reactant properties and fuel cell condition determines the electrical potential difference between the anode and the cathode electrode. The following analysis assumes quasi-static equilibrium and a steady flow of gas and ions.

At the cathode-electrolyte interface, the following half reaction occurs:

(1)      ½O₂ + 2e^– ↔ O^2–

In equilibrium the sum of the chemical potentials is zero:

(2)     

Rearranging equation (2) gives:

(3)     

At the anode-electrolyte interface, the following half reaction occurs:

(4)     H₂ + O^2– ↔ H₂O + 2e^–

In equilibrium the sum of the chemical potentials is zero:

(5)     

Rearranging equation (5) gives:

(6)     

Hence we can calculate the electric potential difference between the anode and the cathode:

(7)     

Assuming that the gases behave like ideal gases, we can write for the chemical potential:

(8)     

x_i is the mole fraction of component i, m^o(T) is the chemical potential per mole of an ideal gas at p_o = 1 bar.

Substituting (8) in (7), we can write:

(9)     

 

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