Identification of active sites in an electrocatalyst is essential for understanding of the mechanism of electrocatalytic water splitting. To be one of the most active oxygen evolution reaction catalysts in alkaline media, Ni–Fe based compounds have attracted tremendous attention, while the role of Ni and Fe sites played has still come under debate. Herein, by taking the pyrrhotite Fe₇S₈ nanosheets with mixed-valence states and metallic conductivity for examples, we illustrate that Fe could be a highly active site for electrocatalytic oxygen evolution. It is shown that the delocalized electrons in the ultrathin Fe₇S₈ nanosheets could facilitate electron transfer processes of the system, where d orbitals of Fe^II and Fe^III would be overlapped with each other during the catalytic reactions, rendering the ultrathin Fe₇S₈ nanosheets to be the most efficient Fe-based electrocatalyst for water oxidation. As expected, the ultrathin Fe₇S₈ nanosheets exhibit promising electrocatalytic oxygen evolution activities, with a low overpotential of 0.27 V and a large current density of 300 mA cm^–2 at 0.5 V. This work provides solid evidence that Fe could be an efficient active site for electrocatalytic water splitting.

中文翻译：

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超薄硫铁矿Fe ₇ S ₈纳米片中的高活性Fe位点，可实现高效的电催化氧释放

识别电催化剂中的活性位点对于理解电催化水分解的机理至关重要。作为碱性介质中最活跃的氧气释放反应催化剂之一，Ni-Fe基化合物引起了极大的关注，而Ni和Fe位点的作用仍在争论中。在此，以具有混合价态和金属电导率的黄铁矿Fe ₇ S ₈纳米片为例，说明Fe可能是电催化氧放出的高活性位点。结果表明，超薄Fe ₇ S ₈纳米片中的离域电子可以促进系统的电子转移过程，其中Fe ^II的d轨道Fe ₇ S ₈纳米片和Fe ^III在催化反应过程中会相互重叠，从而使其成为水氧化过程中最有效的基于Fe的电催化剂。正如预期的那样，超薄的Fe ₇ S ₈纳米片表现出令人鼓舞的电催化氧释放活性，在0.2 V下的过电势低，在0.5 V下的电流密度大，为300 mA cm ^–2。电催化水分解的活性位点。