Monoclinic zirconia-supported Fe 3O 4 for the two-step water-splitting thermochemical cycle at high thermal reduction temperatures of 1400–1600 °C

Abstract

Two-step thermochemical water-splitting using monoclinic ZrO 2-supported Fe 3O 4 (Fe 3O 4/ m-ZrO 2) for hydrogen production was examined at high thermal reduction temperatures of 1400–1600 °C. After thermal reduction of Fe 3O 4/ m-ZrO 2, the reduced sample was quenched in liquid nitrogen, and was subsequently subjected to the water-decomposition step at 1000 °C. Quenching of the solid sample was conducted for analysis of the chemical reactions, such as phase transitions, occurring at high-temperature. The hydrogen productivity of Fe 3O 4 on a m-ZrO 2 support and the conversion of Fe 3O 4 to FeO were significantly enhanced with higher thermal reduction temperatures. The Fe 3O 4-to-FeO conversion reached 60% when the Fe 3O 4/ m-ZrO 2 was thermally reduced at 1600 °C. The phase transition of m-ZrO 2 support to tetragonal ZrO 2 ( t-ZrO 2) did not occur during the thermal reduction at 1400–1500 °C, but it did proceed slightly at 1600 °C. Fe ions from Fe 3O 4 did not enter the ZrO 2 lattice during high-temperature thermal reduction. Thus, the Fe 3O 4 loaded on a m-ZrO 2 support can continuously contribute as a Fe 3O 4–FeO redox reactant for thermochemical water-splitting at high-temperatures of 1400–1600 °C.