The leakage current, (A), models the overall effect of species cross-over from one electrode to another across the electrolyte. In addition to the source terms expressed by Equation 20–72 through Equation 20–80, the following extra volumetric source terms are added to the corresponding equations:

For PEMFC and SOFC:

(20–99)

(20–100)

(20–101)

For SOEC:

(20–102)

(20–103)

(20–104)

Here, and are the he volumes of the catalytic layers on the anode and cathode sides, and 2 and 4 are  the numbers of electrons per mole of reactants and products.