NiFe and CoFe (MFe) layered double hydroxides (LDHs) are among the most active electrocatalysts for the alkaline oxygen evolution reaction (OER). Herein, we combine electrochemical measurements, operando X-ray scattering and absorption spectroscopy, and density functional theory (DFT) calculations to elucidate the catalytically active phase, reaction center and the OER mechanism. We provide the first direct atomic-scale evidence that, under applied anodic potentials, MFe LDHs oxidize from as-prepared α-phases to activated γ-phases. The OER-active γ-phases are characterized by about 8% contraction of the lattice spacing and switching of the intercalated ions. DFT calculations reveal that the OER proceeds via a Mars van Krevelen mechanism. The flexible electronic structure of the surface Fe sites, and their synergy with nearest-neighbor M sites through formation of O-bridged Fe-M reaction centers, stabilize OER intermediates that are unfavorable on pure M-M centers and single Fe sites, fundamentally accounting for the high catalytic activity of MFe LDHs.

中文翻译：

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NiFe和CoFe层状双氢氧化物在析氧过程中的原位结构和催化机理。

NiFe和CoFe（MFe）层状双氢氧化物（LDHs）是用于碱性氧释放反应（OER）的最具活性的电催化剂。在这里，我们结合了电化学测量，操作X射线散射和吸收光谱以及密度泛函理论（DFT）计算来阐明催化活性相，反应中心和OER机理。我们提供了第一个直接的原子级证据，即在施加的阳极电势下，MFe LDHs从制备的α相氧化为活化的γ相。OER活性γ相的特征是晶格间距收缩约8％，并且插层离子发生转换。DFT计算显示，OER通过Mars van Krevelen机制进行。表面铁位点的柔性电子结构，