Thermodynamics and energy engineering

In this chapter the underlying thermodynamic principles that affect solid oxide fuel cell (SOFC)-based systems are reviewed. From classical thermodynamics applied to heat engines, the differences between cyclic engines and fuel cell engines are illustrated. The inapplicability of the Carnot engine (for thermodynamic cycles) to fuel cells (not a cycle, but a steady-state process) is emphasized.

For fuel cells, the actual performance efficiency was, and to an extent continues to be, defined by the First Law, but there is an increasing awareness toward a more effective and meaningful representation of energy usable for work—hence the terms exergy and exergetic efficiency.

Based on a review of several SOFC-combined cycles, it is clear that the maximum exergy destruction occurs at the SOFC stack. Therefore the exergy approach is useful in directing research efforts toward enhancing cell performance, which can include electrode or electrolyte materials, electrode microstructure, and multifunctional electrocatalysts in the anode.

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