Ni–Fe layered double hydroxides (LDHs) are promising for catalyzing the oxygen evolution reaction (OER) in alkaline media. However, the OER mechanism is highly debated, partially because of the lack of an ideal catalyst with 100% exposed active sites for unambiguous characterization. Herein, we develop an alcohol intercalation method to prepare ultrathin Ni–Fe LDH with a 1/3 unit-cell thickness and 100% exposed active sites. The ultrathin LDH catalyst exhibits an intrinsic activity similar to the bulk LDH and allows a direct and reliable characterization of the catalyst without any interference from “bulk” inactive species. Operando synchrotron X-ray analysis indicates that the metallic ions in ultrathin Ni–Fe LDH are fully oxidized into tetravalence states at low applied potentials and that the OER occurs on the tetravalent Ni and Fe ions following a decoupled proton/electron mechanism. Our findings demonstrate that a full oxidization of metal ions is crucial for highly active NiFe LDHs and that it can be accomplished by engineering ultrathin nanostructures.

中文翻译：

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完全氧化的Ni-Fe层状双氢氧化物，具有100％暴露的活性位点，用于催化氧释放反应

Ni-Fe层状双氢氧化物（LDHs）有望在碱性介质中催化氧释放反应（OER）。但是，对OER机理的争议很大，部分原因是缺乏理想的催化剂，该催化剂具有100％暴露的活性位点以进行明确的表征。在这里，我们开发了一种醇插层方法，以制备具有1/3晶胞厚度和100％暴露的活性位点的超薄Ni-Fe LDH。超薄LDH催化剂显示出与本体LDH相似的内在活性，可对催化剂进行直接可靠的表征，而不受“大量”惰性物质的干扰。Operando同步加速器X射线分析表明，超薄Ni-Fe LDH中的金属离子在低施加电势下被完全氧化成四价态，并且OER发生在质子/电子解耦后的四价Ni和Fe离子上。我们的发现表明，金属离子的完全氧化对于高活性NiFe LDH至关重要，并且可以通过工程化超薄纳米结构来实现。