Given its initially low activity and difficulty in active phase formation, Fe site regulation is rarely touched in FeNi-based oxygen evolution reaction (OER) catalysts. Herein, the Fe sites regulation and activity deciphering are demonstrated by selective phase transformation taking nitrogen-doped carbon confined FeNi nanoparticles derived from FeNi-MIL-MOF pyrolysis as an example; driven by the reduction atmosphere and Kirkendall effect assisted by melamine pyrolysis, some Fe and Ni sites were separated to form metallic Fe and FeNi alloy and the subsequent fluorination process induced the ionic compound FeF formation rather than NiF, offering a good platform to evaluate the influence of active Fe phase for OER catalysis. Theoretical calculations combined with ex-situ and in-situ spectral characterization techniques proved the complete convention of FeF into a high-valent and reactive intermediate state of FeOOH. Considering the stable metallic state of Ni, the largely improved catalytic performance could be attributed to the Fe site regulation and the subsequent synergistic catalysis effect. Compared to the traditional iron-based catalyst, theoretically, the electronic structure of FeF was more conducive to the active FeOOH phase formation and significantly lowered the reaction energy barrier for OER. By addressing the aforementioned problems, low overpotential and good stability for OER catalysts were realized. The current work showed valid proof of the FeNi-based catalysts regulation via Fe sites for energy-relevant catalysis reactions.

中文翻译：

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用于析氧反应的受限 FeNi 纳米颗粒中选择性相变的 Fe 位点调节和活性解密


由于 FeNi 基析氧反应 (OER) 催化剂最初的活性较低且难以形成活性相，因此很少涉及 Fe 位点调控。在此，以 FeNi-MIL-MOF 热解衍生的氮掺杂碳限制 FeNi 纳米粒子为例，通过选择性相变证明了 Fe 位点的调控和活性解密；在还原气氛和柯肯德尔效应的驱动下，三聚氰胺热解辅助下，一些Fe和Ni位点分离，形成金属Fe和FeNi合金，随后的氟化过程诱导形成离子化合物FeF而不是NiF，为评估影响提供了良好的平台用于 OER 催化的活性 Fe 相。理论计算结合异位和原位光谱表征技术证明了 FeF 完全转化为高价活性中间态 FeOOH。考虑到Ni稳定的金属态，催化性能的大幅提高可归因于Fe位点调节和随后的协同催化效应。与传统的铁基催化剂相比，理论上，FeF的电子结构更有利于活性FeOOH相的形成，并显着降低了OER的反应能垒。通过解决上述问题，实现了OER催化剂的低过电势和良好的稳定性。目前的工作有效证明了 FeNi 基催化剂通过 Fe 位点进行能量相关催化反应的调节。