Fuel cells represent the most suitable energy conversion, capable of addressing energy crises and environmental pollution. Recently, as one of nonprecious metal catalysts (NPMCs), the MC@N‐C (M = Fe, Co, Ni, Mo, W) catalysts, especially for Fe₃C encased in carbon layer (denoted as Fe₃C@N‐C) have emerged as promising replacements for costly Pt‐based catalysts for oxygen reduction reaction (ORR). This review highlights the synthetic strategies undertaken such as hard template, soft template, and template‐free methods for deriving enhancements in electrocatalytic activity and durability. It also provides a comparison on the synthetic methods and catalytic performance and points out issues in the ORR measurements and activity comparison. In addition, understanding of the proposed active sites and corresponding mechanisms for ORR are covered. The recent advances shed light on contributions of morphology, hierarchical pore structures, density and dispersion of active sites, and synergistic effects of multiple active sites, which endow Fe₃C@N‐C electrocatalysts with enhanced ORR performance. These interesting effects are attained as a result of increased exposure and accessibility of the active sites to O₂ molecules, faster charge and mass transfer, and finally, protection of active sites by carbon shells. Finally, the challenges and perspectives to further improve performance of Fe₃C@N‐C are discussed.

中文翻译：

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碳基材料中封装的金属碳化物用于电催化氧还原反应的最新进展

燃料电池代表了最适合的能量转换，能够应对能源危机和环境污染。最近，作为一种非贵金属催化剂（NPMC），MC @ N‐C（M = Fe，Co，Ni，Mo，W）催化剂，特别是对于碳层中包裹的Fe ₃ C（表示为Fe _3）C @ N‐C）已经成为有前途的昂贵氧还原反应（ORR）的基于Pt的催化剂的替代品。这篇综述重点介绍了采用的合成策略，例如硬模板，软模板和不使用模板的方法，以增强电催化活性和耐久性。它还提供了合成方法和催化性能的比较，并指出了ORR测量和活性比较中的问题。此外，还包括对建议的活动位点的了解以及ORR的相应机制。最近的进展揭示了赋形于Fe ₃的形态，分层孔结构，活性位点的密度和分散以及多个活性位点的协同效应的贡献。具有增强的ORR性能的C @ N‐C电催化剂。通过增加活性位点对O ₂分子的暴露和可及性，更快的电荷和质量转移以及最终通过碳壳保护活性位点，可以实现这些有趣的效果。最后，讨论了进一步改善Fe ₃ C @ N‐C性能的挑战和前景。