The efficiency of a fuel cell is given by

Question

Professor PC Thomas Classes · Answer

The thermal efficiency, $\eta$ of a fuel conversion device is the amount of useful energy produced relative to the change in enthalpy, $\Delta H$ between the product and feed streams.

$$
\eta=\frac{	ext { useful energy }}{\Delta H}
$$

In an ideal case of an electrochemical converter, such as a fuel cell, the change in Gibb's free energy, $\Delta G$ of the reaction is available as useful electric energy at that temperature of the conversion.
Hence, $\eta_{	ext {ideal }}=\frac{\Delta G}{\Delta H}$