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)Sr_xCrO₃ 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 O₂ 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)Sr_xCrO₃ and the relationship between the extent of oxidation, reduction, and hydroxylation with Sr yield important insight into the surface functionality during electrochemical applications.

中文翻译：

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Sr掺入对La（1-x）SrxCrO3中Cr氧化和水解离的影响

金属氧化物的氧化和还原以及它们与环境的相互作用对材料的稳定性和催化反应的能力起着至关重要的作用。化合价的局部变化和表面被吸附物的形成会影响氧化物的电子结构和化学反应性，但在实验上很难进行探测。本文使用环境压力X射线光电子能谱对La _{（1– x）} Sr _x CrO ₃的钙钛矿氧化物家族中Cr的氧化和还原进行了详细研究。Sr的掺入增加了表面氧化的倾向，导致Cr ⁴⁺和Cr ⁶⁺的存在当与O ₂气体平衡时，主要限制在顶部单元电池中。这些酸性位点容易被还原成Cr ³⁺在平衡用H ₂ ö蒸气，并选自H的解离形成羟基的所得量₂ O为正比于以前氧化的表面位点的密度。La _{（1– x）} Sr _x CrO ₃的氧化还原稳定性的定量以及氧化，还原和Sr羟基化程度之间的关系可以使人们深入了解电化学应用过程中的表面功能。