A large solid-state entropy of reduction increases the thermodynamic efficiency of metal oxides for two-step thermochemical water splitting (TWS). We present a high-throughput density functional theory (HT-DFT) study of more than 11,000 oxide compounds to screen for thermodynamically favorable two-step TWS materials, and identify many materials as potential new candidates for TWS applications. In addition to the configurational entropy associated with oxygen off-stoichiometry, we also examine a different source of entropy, the on-site electronic configurational entropy arising from excitations of electrons distributed over a large number of multiplet states (as in f-electron cations). We find that this electronic entropy is sizable in all lanthanides, and reaches a maximum value of ~4.7 kB per oxygen vacancy for Ce+4 / Ce+3 reduction. The unique and large positive electronic entropy in ceria contributes to its excellent water-splitting properties.

Oxygen off-stoichiometry and defect entropies in solar thermochemical water splitting materials

2019 Spring National Meeting

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