Solar hydrogen production via erbium oxide based thermochemical water splitting cycle

Abstract

The erbium oxide based water splitting (Eb-WS) cycle was thermodynamically studied by using the HSC Chemistry software and databases. The first step of the Eb-WS cycle involves thermal reduction of Er2O3, whereas the second step corresponds to the production of H2 via water splitting reaction. Equilibrium compositions associated with the thermal reduction and water splitting steps were determined by performing HSC simulations. Influence of partial pressure of oxygen (PO2) in the inert purge gas on thermal reduction temperature (TH) and equilibrium compositions associated with the solar thermal dissociation of Er2O3 was identified. Furthermore, energy and exergy analysis of the Eb-WS cycle was carried out to estimate the cycle (ηcycle) and solar-to-fuel conversion efficiency (ηsolar−to−fuel). Simulation results indicate that the ηcycle and ηsolar−to−fuel of Eb-WS cycle increase with the decrease in TH. Also, the ηcycle and ηsolar−to−fuel can be increased further via the recuperation of the heat released by the water splitting reactor and the quench unit. The ηsolar−to−fuel of Eb-WS cycle was observed to be equivalent to that of ceria cycle.