Two-step water splitting for solar H2 production with ZnII–MnII,III–FeIII spinel structure using concentrated solar heat

Two-step water splitting with the MnFe2O4/ZnO/H2O system which can be applied for the solar hydrogen production has been studied. The water splitting reaction with the MnFe2O4/ZnO/H2O system generates H2 at 1273 K, and the ZnII–MnII,III–FeIII spinel type compound is produced. The amount of the H2 generation was 1.7 ml per 2/3 mmol of MnFe2O4, which is 23% of the theoretical yield. The ZnII–MnII,III–FeIII spinel type compound releases the O2 gas in the air flow condition at 1800K, and is decomposed into the stoichiometric MnFe2O4 and the fine particle of the ZnO phase. The fine particle of ZnO was deposited on the surface of the reaction cell wall and formed a thin layer by the back reaction between the metal Zn vapor and the O2 gas. The cyclic process for the two-step water splitting of this system (the MnFe2O4/ZnO/H2O system) was confirmed from the experimental result that the O2 releasing step was carried out using the solid sample obtained after the H2 generation step with the MnFe2O4/ZnO/H2O system.