The different oxidation states of chromium means that its bulk oxide is reducible. This can be important for the oxygen vacancy formation process, which is a key property in applications including catalysis. In a similar way to other reducible metal oxides such as TiO2, and CeO2, the effect of substitutional metal doping of bulk Cr2O3 and its effect on oxygen vacancy formation and the electronic structure are important, with a focus on enhancing the latter. In this contribution we present density functional theory (DFT) calculations with a Hubbard + U correction (DFT+U) applied to the Cr 3d and O 2p states, on pure and metal-doped bulk Cr2O3. The dopants are divalent Mg, Cu, Ni, and Zn and monovalent Li, Na, K and Rb. Given this difference in the host and dopant oxidation states, we show that to predict the correct ground states, the divalent dopants require two metal dopants charge compensated with an oxygen vacancy, which is the ground state. The monovalent dopant ground state has a one oxygen vacancy per dopant. The second oxygen atom removed is termed “the active” oxygen vacancy and it is the energy required to remove this atom that is related to the reduction process. In all cases, we find that substitutional doping improves the oxygen vacancy formation of bulk Cr2O3 by lowering the energy cost. The origins of this arise from dopant ionic radius, dopant coordination and distortion of the local atomic structure around the dopant. These results enhance our understanding of factors that drive reducibility in reducible metal oxides. Support from the European Commission through the 7th Framework Project BIOGO (www.biogo.eu), grant number 604296, is acknowledged

Lower valence metal doping of bulk Cr2O3: Charge compensation and oxygen vacancy formation

253rd National Meeting (2017)

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