Impact of Sr-Incorporation on Cr Oxidation and Water Dissociation in La(1-x)SrxCrO3

The oxidation and reduction of metal oxides and their interaction with the environment play a critical role in material stability and the ability to catalyze reactions. The local change in valence and formation of surface adsorbates affect the oxide electronic structure and chemical reactivity, yet are challenging to probe experimentally. In this paper a detailed study of the oxidation and reduction of Cr in the perovskite oxide family of La(1-x)SrxCrO3 using ambient pressure X-ray photoelectron spectroscopy is presented. The incorporation of Sr increases the propensity to oxidize at the surface, leading to the presence of Cr4+ and Cr6+ principally confined to the top unit cell when in equilibrium with O-2 gas. These acidic sites are readily reduced to Cr3+ in equilibrium with H2O vapor, and the resultant amount of hydroxyls formed from the dissociation of H2O is directly proportional to the density of surface sites formerly oxidized. The quantification of the redox stability of La(1-x)SrxCrO3 and the relationship between the extent of oxidation, reduction, and hydroxylation with Sr yield important insight into the surface functionality during electrochemical applications.