Several novel materials were synthesized by precipitating iron oxide (using the previously optimized 10% Fe loading by weight) onto mixtures of nanoparticle zirconia and ceria to investigate the effects of adding CeO2 to FeOx/ZrO2 materials in the thermochemical water splitting reaction. At water splitting temperatures of 1000 degrees C (after thermal reduction at 1450 degrees C), the stability of the CeO2-containing materials was lower than for the FeOx/ZrO2 material, and there was no advantage to adding CeO2 to the FeOx/ZrO2 material. However, when operating at a water splitting (WS) temperature of 1200 degrees C, the stability increased and the hydrogen production was significantly higher over most materials compared with a water splitting temperature of 1000 degrees C. At a WS temperature of 1200 degrees C the FeOx/Zr75Ce25O2 (75% Zr75O2 and 25% CeO2 by weight) and FeOx/Ce50O2 materials performed slightly better than the FeOx/ZrO2 material, and X-ray photoelectron spectroscopy data revealed that the surface concertation of iron is less important compared with water splitting at 1000 degrees C. The temperature programmed reduction data indicated that the FeOx-CeO2 interactions were weaker compared with FeOx-ZrO2 interactions, since the FeOx. reduction occurred at lower temperatures for the CeO2-containing materials. The weaker interactions can explain why the stability was lower for the materials containing CeO2 (sintering of FeO was likely more pronounced) The X-ray diffraction data revealed that ZrO2-CeO2 solid solutions formed after activation at 1450 degrees C and lattice volume calculations indicated that iron did incorporate into the ZrO2-CeO2 matrices. More incorporation was observed after water-splitting at 1200 degrees C compared with a lower temperature (1000 degrees C), and likely explains why the materials were more stable during water-splitting at 1200 degrees C. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.