A Novel Two-Step Metal Oxide – Metal Sulfate Water Splitting Cycle for the Production of Solar Hydrogen

We propose a novel two step metal oxide – metal sulfate water splitting cycle for the production of hydrogen by using concentrated solar power as a process heat source. It is a two-step process in which the first solar step belongs to the endothermic thermal reduction of metal sulfate into metal oxide, SO₂, and O₂. The second exothermic step corresponds to the non-solar oxidation of metal oxide by SO₂ and H₂O producing metal sulfate and H₂ (metal sulfate and metal oxide can be recycled for the multiple steps in this process). A detailed computational thermodynamic modeling of this process was carried out by investigating different metal sulfate – metal oxide combinations. The thermodynamic equilibrium compositions associated with this process were theoretically determined. Also, the solar reactor efficiency analysis was performed to estimate the maximum solar to hydrogen conversion efficiency. Effect of various process parameters such as reaction temperatures, pressures, reactants/carrier gas flow rates, heat recuperation, etc. were investigated. To study this process, commercially available thermodynamic softwares such as HSC Chemistry and FactSage were used. Results obtained indicate that the efficiency of this process is considerably higher than other metal oxide based thermochemical cycles. The computational thermodynamic analysis will be presented in detail.