Regulating the site density of single-atom catalysts (SACs) promotes the potential to remarkably improve the performance of electrocatalysis, such as the oxygen reduction reaction (ORR). However, the catalytic behaviour governed by individual and interacting sites is particularly elusive and has yet to be understood. Here we demonstrate the origin of the enhancement of the ORR activity of isolated Fe–N₄ SACs over inter-site distances down to the subnanometre level. Strong interactions between adjacent Fe–N₄ moieties alter the electronic structure when the inter-site distance is less than about 1.2 nm, resulting in increased intrinsic ORR activity. The marked improvement in site performance continues until neighbouring Fe atoms approach as close as about 0.7 nm, below which the intrinsic activity is slightly diminished. The present study highlights the significance of identifying the fundamental mechanism of the inter-site distance effect in Fe–N₄ catalysts for the ORR, which may promote the full potential of densely populated SACs.

调节单原子催化剂 (SAC) 的位点密度有助于显着提高电催化性能，例如氧还原反应 (ORR)。然而，由单个和相互作用位点控制的催化行为特别难以捉摸，尚待理解。_{在这里，我们证明了分离的 Fe-N 4} SAC的 ORR 活性在位点间距离上提高到亚纳米级的起源。_{相邻 Fe-N 4}之间的强相互作用当位点间距离小于约 1.2 nm 时，部分会改变电子结构，导致内在 ORR 活性增加。位点性能的显着改善一直持续到相邻的 Fe 原子接近约 0.7 nm，低于此值的本征活性略有降低。本研究强调了确定用于 ORR 的 Fe-N ₄催化剂中位点间距离效应的基本机制的重要性，这可能会促进高密度 SAC 的全部潜力。