Thermochemical two-step water splitting cycles by monoclinic ZrO2-supported NiFe2O4 and Fe3O4 powders and ceramic foam devices

A thermochemical two-step water splitting cycle is examined for NiFe2O4 and Fe3O4 supported on monoclinic ZrO2 (NiFe2O4/m-ZrO2 and Fe3O4/m-ZrO2) in order to produce hydrogen from water at a high-temperature. The evolution of oxygen and hydrogen by m-ZrO2-supported ferrite powders was studied, and reproducible and stoichiometric oxygen/hydrogen productions were demonstrated through a repeatable two-step reaction. Subsequently, a ceramic foam device coated with NiFe2O4/m-ZrO2 powder was made and examined as a water splitting device by the direct irradiation of concentrated Xe-light in order to simulate solar radiation. The reaction mechanism of the two-step water splitting cycle is associated with the redox transition of ferrite/wustite on the surface of m-ZrO2. A hydrogen/oxygen ratio for these redox powder systems exhibited good reproducibility of approximately two throughout the repeated cycles. The foam device loaded NiFe2O4/m-ZrO2 powder was also successful with respect to hydrogen production through 10 repeated cycles. A ferrite conversion of 24–76% was obtained over an irradiation period of 30 min.