Cerium ion redox system in CeO2-xFe2O3 solid solution at high temperatures (1,273-1,673 K) in the two-step water-splitting reaction for solar H2 generation

CeO2-xFe(2)O(3) (x = 0.026-0.214) solid solutions with different Ce:Fe mole ratios (Ce:Fe = 9.5:0.5-7.0:3.0) were prepared as reactive ceramics with the combustion method for solar hydrogen production. The prepared CeO2-xFe(2)O(3) solid solutions were characterized by X-ray diffractometry, ICP atomic emission spectrometry, and Mossbauer spectroscopy. Two-step water-splitting reaction with the CeO2-xFe(2)O(3) solid solution proceeded at 1,673 K for the O-2-releasing reaction and at 1,273 K for the H-2-generation reaction by irradiation of an infrared imaging lamp as a solar simulator. The amounts of H-2 gas evolved in the H-2-generation reaction with CeO2-xFe(2)O(3) solid solutions were 0.97-1.8 cm(3)/g, the evolved H-2/O-2 ratio was approximately equal to 2 of the stoichiometric value. The amounts of H-2 and O-2 gases were independent of the Ce:Fe mole ratio in the CeO2-xFe(2)O(3) solid solution. It was suggested that the O-2-releasing and H-2-generation reactions with the CeO2-xFe(2)O(3) solid solution were repeated with the reduction and oxidation of Ce4+-Ce3+ enhanced by the presence of Fe3+-Fe2+.