Two-step water splitting with Ni-ferrite (NiFe2O4) system for H2 production using concentrated solar thermal was examined. The O2 releasing reaction proceeded in air at 1800K by irradiation with Xe lamp beams which were used as a solar simulator. The stoichiometry and the reaction mechanism of the O2 releasing step were investigated by XRD. The reaction yield was estimated to be 48% from the calculation of the spinel phase lattice constant, and the XRD showed that the solid solution phase of (Ni, Fe)O between NiO and FeO was formed. The (Ni, Fe)O solid solution could lower the O2 releasing reaction temperature. In the H2 generating step for the sample obtained by the O2 releasing step, the reaction proceeded very fast and its yield was 90% of the theoretical one at 1123K. The XRD measurement indicated that the (Ni, Fe)O solid solution phase was changed to the spinel phase of Ni-ferrite in the H2 generation step.

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