Hydrogen production from mixed cerium oxides via three-step water-splitting cycles

This study deals with the production of hydrogen from water-splitting thermochemical cycles based on mixed metal oxides. The solar synthesis of mixed oxides based on ceria was achieved by melting mixed powders of component oxides at high temperature. The reduced oxides (Ce2Ti2O7, Ce2Si2O7, CeFeO3, CeVO4, and CeNbO4) produced hydrogen in a three-step thermochemical cycle except CeVO4. The three-step cycle uses an alkali hydroxide (NaOH or KOH) in an activation reaction to improve oxidation and to facilitate water-splitting during the third step. Experimental investigations were performed to demonstrate the concept and to quantify the reactions performance for hydrogen production. The high temperature synthesis of reduced cerium-based mixed oxides was performed in a laboratory-scale solar reactor. The mixed oxides were analysed by X-ray diffraction and characterized by XPS, which identified Ce(III) species in the structure. The activation reaction with NaOH or KOH producing hydrogen was studied to determine the effect of temperature and particle diameter, and to quantify the chemical conversion for each cerium-based mixed oxide.