Reduction reactivity of CeO2-ZrO2 oxide under high O2 partial pressure in two-step water splitting process

摘要

The O2-releasing reaction under the air with the reactive ceramics of CeC>2-ZrO2 oxides which can be applied to solar hydrogen production via a two-step water splitting cycle using concentrated solar thermal energy was investigated. CeO2-ZrO2 oxides were synthesized by polymerized complex method at different Ce:Zr molar ratio. The solid solubility of ZrO2 in fluorite structure of CeO2 was in good agreement with the initial content of Zr ions at the preparation in CeO2-ZrO2 oxide. The (^-releasing reaction in air with CeC>2-ZrO2 oxides was studied. Different solid solubility (0%, 10%, 20%, 30%) of ZrC>2 in CeC>2 were examined. The amount of O2 gas evolved in the reaction with Cei_xZrxO2 (0 ^ x $J 0.3) solid solutions was more than that with CeC>2, and the largest yield of 2.9 cm3/g was exhibited at x =0.2 (Ceo.8Zro.2O2) for an O2 release at 1500 °C in air. The reduced cerium ion in Ceo.8Zro.2O2 was about 11%, which is seven times higher than that with CeO2. The optical absorption and luminescence spectra of the CeO2-ZrO2 oxide obtained before and after the O2-releasing reaction suggest that the reduction of Ce4+ with formation of oxygen defect in the air. The enhancement of the O2-releasing reaction with CeO2-ZrO2 oxide is found to be caused by an introduction of Zr4+, which has smaller ionic radius than Ce3+ or Ce4+, in the fluorite structure.