Efficiency of ideal fuel cell and Carnot cycle from a fundamental perspective

Abstract

In this paper, we accept the fact that fuel cell and heat engine efficiencies are both constrained by the second law of thermodynamics and neither one is able to break this law. However, we have shown that this statement does not mean the two systems should have the same maximum thermal efficiency when being fed by the same amounts of chemical reactants. The intrinsic difference between fuel cells (electrochemical systems) and heat engines (combustion engines) efficiencies is a fundamental one with regard to the conversion of chemical energy of reactions into electrical work. The sole reason has been shown to be due to the combustion irreversibility of the latter. This has led to the statement that fuel cell efficiency is not limited by the Carnot cycle. Clarity is achieved by theoretical derivations and several numerical examples.