We boost the ORR performance of Fe–N–C electrocatalysts in acids by engineering highly accessible and dense surface single metal FeN₄ active sites.

Single‐atom catalysts (SACs), as promising alternatives to Pt‐based catalysts, suffer from the limited choice of center metals and low single‐atom loading. Here, we report a pentacoordinated Zr‐based SAC with nontrivial axial O ligands (denoted O−Zr−N−C) for oxygen reduction reaction (ORR). The O ligand downshifts the d‐band center of Zr and confers Zr sites with stable local structure and proper adsorption capability for intermediates. Consequently, the ORR performance of O−Zr−N−C prominently surpasses that of commercial Pt/C, achieving a half‐wave potential of 0.91 V vs. reversible hydrogen electrode and outstanding durability (92 % current retention after 130‐hour operation). Moreover, the Zr site shows good resistance towards aggregation, enabling the synthesis of Zr‐based SAC with high loading (9.1 wt%). With the high‐loading catalyst, the zinc‐air battery (ZAB) delivers a record‐high power density of 324 mW cm⁻² among those of SAC‐based ZABs.