Thermochemical two-step water splitting by internally circulating fluidized bed of NiFe 2O 4 particles: Successive reaction of thermal-reduction and water-decomposition steps

Abstract

Thermochemical two-step water splitting using a redox system of iron-based oxides or ferrites is a promising process for producing hydrogen without CO 2 emission by the use of high-temperature solar heat as an energy source and water as a chemical source. In this study, thermochemical hydrogen production by two-step water splitting was demonstrated on a laboratory scale by using a single reactor of an internally circulating fluidized bed. This involved the successive reactions of thermal-reduction (T-R) and water-decomposition (W-D). The internally circulating fluidized bed was exposed to simulated solar light from Xe lamps with an input power of 2.4–2.6 kW th for the T-R step and 1.6–1.7 kW th for the subsequent W-D step. The feed gas was switched from an inert gas (N 2) in the T-R step to a gas mixture of N 2 and steam in the W-D step. NiFe 2O 4/ m-ZrO 2 and unsupported NiFe 2O 4 particles were tested as a fluidized bed of reacting particles, and the production rate and productivity of hydrogen and the reactivity of reacting particles were examined.