Ce_0.67Cr_0.33O_2.11: a new low-temperature O₂ evolution material and H₂ generation catalyst by thermochemical splitting of water

Abstract

Ce_0.67Cr_0.33O_2.11 was synthesized by hydrothermal method using diethylenetriamine as complexing agent (Chem. Mater. 2008, 20, 7268). Ce_0.67Cr_0.33O_2.11 being the only compound likes UO_2+δto have excess oxygen, it releases a large proportion of its lattice oxygen (0.167 M [O]/mole of compound) at relatively low temperature (465 °C) directly and it has been utilized for generation of H₂ by thermo-splitting of water. An almost stoichiometric amount of H₂ (0.152 M/Mole of compound) is generated at much lower temperature (65 °C). There is an almost comparable amount of oxygen release and hydrogen generation over this material at very low temperature compared to other CeO₂-MO_x (Mn, Fe, Cu, and Ni) mixed-oxide solid solutions (O₂ evolution ≥1300 °C and H₂ generation at 1000 °C). The reversible nature of oxygen release and intake of this material is attributed to its fluorite structure and coupling between the Ce^4+/6+/Ce³⁺ and Cr⁴⁺/Cr³⁺ redox couples. Compound shows reversible oxygen release and intake by H₂O absorption and subsequent hydrogen release to gain parent structure and hence this material can be utilized for generation of H₂ at very low temperature by thermo-chemical splitting of water.