Solar hydrogen generation with H2O/ZnO/MnFe2O4 system

The hydrogen generation reaction in the H2O/ZnO/MnFe2O4 system was studied to clarify the possibility of whether this reaction system can be used for the two-step water splitting to convert concentrated solar heat to chemical energy of H2. At 1273 K, the mixture of ZnO and MnFe2O4 reacted with water to generate H2 gas in 60% yield. X-ray diffractometry and chemical analysis showed that 48 mol% of MnII (divalent manganese ion) in the A-site of MnFe2O4 was substituted with ZnII (divalent zinc ion) and that chemical formula of the solid product was estimated to be Zn0:58MnII 0:42MnIII 0:39Fe1:61O4 (MnIII: trivalent manganese ion). Its lattice constant was smaller than that of the MnFe2O4 (one of the two starting materials). From the chemical composition, the reaction mechanism of the H2 generation with this system was discussed. Since the Mn ions in the product solid after the H2 generation reaction are oxidized to Mn3þ, which can readily release the O2 ions as O2 gas around 1300 K, the two-step of H2 generation and O2 releasing seem to be cyclic. 2003 Elsevier Ltd. All rights reserved.