H₂ Generation by Two-Step Water Splitting With CeO₂-MO_x Using Concentrated Solar Thermal Energy

CeO₂-MO_x (M = Mn, Fe, Ni, Cu) reactive ceramics, having high melting points and high conductivities of O²⁻, were synthesized with the combustion method from their nitrates for solar hydrogen production. The prepared CeO₂-MO_x samples were solid solutions between CeO₂ and MO_x with the fluorite structure through XRD. Two-step water splitting reactions with CeO₂-MO_x reactive ceramics proceeded at 1573–1773K for the O₂ releasing step and at 1273K for the H₂ generation step by irradiation of infrared imaging furnace as a solar simulator. The amounts of O₂ evolved in the O₂ releasing reaction with CeO₂-MO_x and CeO₂ systems increased with the increase of the reaction temperature. The amounts of H₂ evolved in the H₂ generation reaction with CeO₂-MO_x systems except for M = Cu were more than that of CeO₂ system after the O₂ releasing reaction at the temperatures of 1673 and 1773K. The largest amount of H₂ was generated with CeO₂-NiO after the O₂ releasing reaction at 1573, 1673 and 1773K. The O₂ releasing reaction at 1673K and H₂ generation reaction at 1273K with CeO₂-Fe₂O₃ were repeated four times with the evolving of O₂ (1.3cm³/g-sample) and H₂ (2.3cm³/g-sample) gases, respectively. The possibility of solar hydrogen production with CeO₂-MO_x (M = Mn, Fe, Ni) reactive ceramics system by using concentrated solar thermal energy was suggested.