Abstract
Efficiency of hydrogen fuel cells is analyzed using a non-equilibrium theory of mixtures based on classical irreversible thermodynamics. The efficiency is expressed in terms of processes taking place inside the fuel cells revealing which processes are responsible for efficiency losses.
This provides a new method of optimization. It is shown that efficiency losses are not only given by entropy production rate but also by some additional terms, which become important if steep gradients of temperature are present.
Consequently, we compare the new theory with the standard entropy production minimization approach. Finally, we discuss effects of the additional terms in polymer electrolyte membrane fuel cells and in solid oxide fuel cells showing that the new theory gives the same results as the standard theory in the former case while it becomes important in the latter case.