Reactive ceramics of CeO2-MOx (M = Mn, Fe, Ni, Cu) for H2 generation by two-step water splitting using concentrated solar thermal energy

The addition of MOx (M: di- or tri-valent transition metal ion) into cerium dioxide (CeO2) enhanced the ability of CeO2 for the oxygen (O-2)-releasing reaction at lower temperature and swift hydrogen (H-2)-generation reaction. CeO2-MOx (M = Mn, Fe, Ni, Cu) reactive ceramics having high melting points were synthesized with the combustion method from their nitrates for solar H-2 production. The prepared CeO2-MOx samples were solid solutions between CeO2 and MOx with the fluorite structure through the X-ray diffractometry measurement. Two-step water-splitting reactions with CeO2-MOx reactive ceramics proceeded at 1573-1773 K for the O-2-releasing step and at 1273 K for the H-2-generation step by irradiation of infrared image furnace as a solar simulator. The amounts of O-2 evolved in the O-2-releasing reaction with CeO2-MOx increased with an increase in the reaction temperature. The amounts of H-2 evolved in the H-2-generation reaction with CeO2-MOx systems except for M = Cu were more than that of CeO2 system after the O-2-releasing reaction at the temperatures of 1673 and 1773 K. The amounts of H-2 evolved in the H-2-generation reaction with CeO2-MnO and CeO2-NiO systems were more than those of CeO2-Fe2O3, CeO2-Cu-2 and CeO2 systems after the O-2-releasing reaction at the temperature of 1573 K. The amounts of evolved H-2 after the O-2-releasing reaction at the temperature of 1773 K in cm(3) per gram of CeO2-MOx were 0.975-3.77 cm(3)/g. The O-2-releasing reaction at 1673 K and H-2-generation reaction at 1273 K with CeO2-Fe2O3 proceeded with repetition of 4 times stoichiometrically. (c) 2006 Elsevier Ltd. All rights reserved.