Metal oxide materials may be used in two-step solar thermochemical water-splitting cycles to renewably produce hydrogen.  Here, we use first-principles density functional calculations to investigate promising oxide materials for use in these cycles.  We present a general analysis of the equilibrium thermodynamics of a two-step metal oxide water splitting cycle, and survey a large number (more than 100) binary oxide redox couples. This analysis strongly suggest the use of non-stoichiometric oxides in gas splitting cycles. Hence, we perform a kinetic and thermodynamic analysis of the mechanism for water splitting on reduced CeO2-x (111). We show the unreactive behaviour at low temperature is caused by kinetically limited diffusion of vacancies from the subsurface to the surface, while the remarkable reduction of reduced CeO2-x(111) at high temperature, where only H2 desorption is slow, may be explained by the formation of a thermodynamically stable hydroxyl layer.

Solar fuels from thermochemical gas splitting

245th National Meeting (2013)

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