Single-atom catalysts (SACs), with the utmost atom utilization, have attracted extensive interests for various catalytic applications. The coordination environment of SACs has been recognized to play a vital role in catalysis while their precise regulation at atomic level remains an immense challenge. Herein, a post metal halide modification (PMHM) strategy has been developed to construct Ni-N₄ sites with axially coordinated halogen atoms, named Ni₁N-C (X) (X = Cl, Br, and I), on pre-synthetic nitrogen-doped carbon derived from metal-organic frameworks. The axial halogen atoms with distinct electronegativity can break the symmetric charge distribution of planar Ni-N₄ sites and regulate the electronic states of central Ni atoms in Ni₁N-C (X) (X = Cl, Br, and I). Significantly, the Ni₁N-C (Cl) catalyst, decorated with the most electronegative Cl atoms, exhibits Faradaic efficiency of CO up to 94.7% in electrocatalytic CO₂ reduction, outperforming Ni₁N-C (Br) and Ni₁N-C (I) catalysts. Moreover, Ni₁N-C (Cl) also presents superb performance in Zn-CO₂ battery with ultrahigh CO selectivity and great durability. Theoretical calculations reveal that the axially coordinated Cl atom remarkably facilitates *COOH intermediate formation on single-atom Ni sites, thereby boosting the CO₂ reduction performance of Ni₁N-C (Cl). This work offers a facile strategy to tailor the axial coordination environments of SACs at atomic level and manifests the crucial role of axial coordination microenvironments in catalysis.

单原子催化剂（SACs）具有最大的原子利用率，在各种催化应用中引起了广泛的兴趣。SACs的协调环境已被认为在催化中发挥着至关重要的作用，而它们在原子水平上的精确调控仍然是一个巨大的挑战。在此，开发了一种后金属卤化物改性 (PMHM) 策略，以在预合成氮上构建具有轴向配位卤素原子的 Ni-N _{4位点，命名为 Ni 1} N-C (X) (X = Cl、Br 和 I)源自金属有机框架的掺杂碳。具有明显电负性的轴向卤素原子可以打破平面Ni-N _{4位点的对称电荷分布，调节Ni 1}中中心Ni原子的电子态NC (X)（X = Cl、Br 和 I）。值得注意的是，Ni _{1 N-C (Cl) 催化剂装饰有最具负电性的 Cl 原子，在电催化 CO 2}还原中表现出高达 94.7% 的 CO 法拉第效率，优于 Ni ₁ N-C (Br) 和 Ni ₁ N-C (I) 催化剂。此外，Ni ₁ N-C (Cl) 在 Zn-CO ₂电池中也表现出优异的性能，具有超高的 CO 选择性和出色的耐用性。理论计算表明，轴向配位的Cl原子显着促进了单原子Ni位点上*COOH中间体的形成，从而提高了Ni _{1的CO 2}还原性能数控（氯）。这项工作为在原子水平上定制 SACs 的轴向配位环境提供了一种简便的策略，并体现了轴向配位微环境在催化中的关键作用。