Graphitic layer encapsulated iron based nanoparticles (G@FeNPs) have recently been disclosed as an interesting type of highly active electrocatalysts for the oxygen reduction reaction (ORR). However, the complex composition of the metal-containing components and their contributions in catalysis remain unclear. As a representative catalyst of the unique encapsulated structure, a series of G@FeNPs catalysts were prepared by a high-pressure pyrolytic process with uniform and essentially identical morphologies but varied compositions. The catalysts exhibited a high onset potential of 0.85 V at 0.1 mA cm⁻² in acidic media. By ⁵⁷Fe-Mössbauer spectroscopy the iron containing components were identified including α-Fe, γ-Fe, γ-Fe₂O₃, and Fe₃C as well as a minor doublet component due to Fe³⁺ in high spin and/or Fe²⁺ in low spin state. The ORR activities are evaluated in terms of the mass specific kinetic current density found to be positively correlated with the Fe₃C content in the range of study, indicating involvement of the encapsulated nanoparticles in the ORR catalysis. The recognition of the Fe compositions and active sites provides new insights to the confined Fe-based ORR electrocatalysts and therefore options for further development of non-precious metal materials.

中文翻译：

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⁵⁷石墨层密封的铁电催化剂的氧还原反应的铁穆斯堡尔谱和电化学活动

石墨层封装的铁基纳米粒子（G @ FeNPs）最近已被公开作为一种有趣的氧还原反应（ORR）高活性电催化剂类型。然而，含金属组分的复杂组成及其在催化中的作用仍不清楚。作为独特包封结构的代表性催化剂，通过高压热解法制备了一系列G @ FeNPs催化剂，它们具有均匀且基本相同的形貌，但组成不同。所述催化剂在酸性介质中在0.1mA cm ^-2下显示出0.85V的高起始电位。通过⁵⁷的Fe-穆斯堡尔谱含有组分的铁被确定包括的α-Fe，γ-铁，γ-的Fe ₂ ö ₃，和Fe由于在高自旋状态下为Fe ³⁺和/或在低自旋状态下为Fe ²⁺，因此具有₃ C以及次要的双峰态成分。根据在研究范围内发现的与Fe ₃ C含量呈正相关的质量比动电流密度来评估ORR活性，表明包封的纳米颗粒参与了ORR催化。铁成分和活性位点的识别为有限的铁基ORR电催化剂提供了新的见识，因此为进一步开发非贵金属材料提供了选择。