Transition metal nitride (TMN-) based materials have recently emerged as promising non-precious-metal-containing electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media. However, the lack of fundamental understanding of the oxide surface has limited insights into structure–(re)activity relationships and rational catalyst design. Here we demonstrate how a well-defined TMN can dictate/control the as-formed oxide surface and the resulting ORR electrocatalytic activity. Structural characterization of MnN nanocuboids revealed that an electrocatalytically active Mn₃O₄ shell grew epitaxially on the MnN core, with an expansive strain along the [010] direction to the surface Mn₃O₄. The strained Mn₃O₄ shell on the MnN core exhibited an intrinsic activity that was over 300% higher than that of pure Mn₃O₄. A combined electrochemical and computational investigation indicated/suggested that the enhancement probably originates from a more hydroxylated oxide surface resulting from the expansive strain. This work establishes a clear and definitive atomistic picture of the nitride/oxide interface and provides a comprehensive mechanistic understanding of the structure–reactivity relationship in TMNs, critical for other catalytic interfaces for different electrochemical processes.

基于过渡金属氮化物 （TMN-） 的材料最近成为一种很有前途的非含贵金属电催化剂，用于碱性介质中的氧还原反应 （ORR）。然而，缺乏对氧化物表面的基本理解，限制了对结构-（再）反应性关系和合理催化剂设计的了解。在这里，我们演示了定义明确的 TMN 如何决定/控制形成的氧化物表面和由此产生的 ORR 电催化活性。MnN 纳米长方体的结构表征表明，电催化活性的 Mn₃O₄ 壳层在 MnN 核心上外延生长，沿 [010] 方向向 Mn₃O₄ 表面发出膨胀应变。MnN 核上应变的 Mn₃O₄ 壳层表现出比纯 Mn₃O₄ 高 300% 以上的内禀活性。电化学和计算相结合的研究表明/表明，增强可能源于膨胀应变产生的更羟基化的氧化物表面。这项工作建立了氮化物/氧化物界面的清晰明确的原子图景，并提供了对 TMN 中结构-反应性关系的全面机理理解，这对于不同电化学过程的其他催化界面至关重要。