Limiting thermodynamic efficiencies of thermochemical cycles used for hydrogen generation

Abstract

Thermochemical cycles can provide a transformation mechanism for highly endothermic reactions at moderate temperatures and worthwhile yields but without the generation of waste streams. These have a general applicability but have been predominantly used for energy transformation from heat to stored chemical free energy in the form of hydrogen, with a view to a future hydrogen economy. Thermal efficiency is a key parameter in such a transformation, and the study presents a simple methodology for the determination of the limiting efficiency available, for the purpose of decision making in further cycle implementation and to develop consistency with other heat-to-work processes. The method is applied to 21 previously reported cycles, for which no such efficiency information has been reported, and discusses the features of the cycles which give rise to high and low efficiencies.