A methodology has been developed for the evaluation of thermochemical and hybrid water-splitting cycles based on energy efficiency. Efficiency is referenced to the standard enthalpy of formation of water at 298K and includes minimum hot utility requirements, electrical work to power electrochemical reactions as well as power and heat required for separation processes. In addition, equilibrium conversions were considered. The degrees of freedom of each cycle (temperatures, pressures and excess reactants) were considered and these values were varied to optimized efficiency. Different separation schemes were also considered: recycling reactants to the same reactor or considering other strategic options. Results are shown for three different configurations considered for each of ten chosen cycles. These results show that separation decisions can greatly improve cycle efficiency.
