• thermochemical cycles;
  • nickel ferrite;
  • solar hydrogen;
  • water splitting;
  • thermal reduction

Water splitting — thermal reduction cyclic studies with NiFe2O4 redox materials were performed in a differential fixed-bed laboratory reactor in the temperature range 700–1,400°C to quantify the effects of operation temperatures and steam mole fraction on hydrogen and oxygen yields. Hydrogen yield increased drastically by an increase of the water splitting temperature from 800 to 1,000°C reaching a plateau at 1,100°C. In parallel, a simple mathematical model was formulated describing the water splitting process via the heterogeneous surface reactions of water vapor with the redox powder material, from which, in conjunction to the aforementioned experiments, the kinetic parameters of the water splitting and thermal reduction reactions were extracted. The water splitting kinetic constants exhibited weak temperature dependence between 700 and 1,100°C suggesting the existence on the redox material of more than one type of oxygen storage sites with respect to ease of exposure and accessibility to the gas phase. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1213–1225, 2013