The thermochemical two-step water splitting was examined on ZrO2-supported Co(II)-ferrites below 1400 degrees C, for purpose of converting solar high-temperature heat to clean hydrogen energy as storage and transport of solar energy. The ferrite on the ZrO2-support was thermally decomposed to the reduced phase of wustite at 1400 degrees C under an inert atmosphere. The reduced phase was reoxidized with steam on the ZrO2-support to generate hydrogen below 1000 degrees C in a separate step. The ZrO2-supporting alleviated the high-temperature sintering of iron oxide. As the results, the ZrO2-supported ferrite realized a greater reactivity and a better repeatability of the cyclic water splitting than the conventional unsupported ferrites. The CoxFe3-xO4/ZrO2 with the x value of around 0.4-0.7 was found to be the promising working material for the two-step water splitting when thermally reduced at 1400 degrees C under an inert atmosphere. (c) 2004 Published by Elsevier Ltd.