Nanocage Carbon via In Situ Gas‐Phase Anisotropic Etching: Synergistically Enhancing the Intrinsic Activity and Utilization Efficiency of Active Sites for ORR

The performance of Fe–N–C catalysts in the oxygen reduction reaction (ORR) is governed not only by their intrinsic activity but also by the accessibility of their active sites, which is a vital yet frequently overlooked metric referred to as atomic utilization efficiency (UE). Herein, we propose an innovative in situ gas‐phase anisotropic etching approach to construct a open nanocage carbon to simultaneously achieve asymmetric Fe–N 3v P active sites and ultrahigh UE of these sites. Specifically, during the low‐temperature pyrolysis, NH 3 gas generated from the thermal decomposition of diammonium phosphate ((NH 4 ) 2 HPO 4 ) in the hybrid precursor acts as a Lewis base to selectively etch the {100} facets of ZIF‐8 with high density coordination bonds. Subsequently, stress‐induced contraction effect drives a further hollowing process to form the unique open nanocage carbon during the high‐temperature pyrolysis. This two‐in‐one strategy boosts the intrinsic activity of the unit active site (a high turnover frequency of 2.87 e site −1 s −1 ) and reaches an ultrahigh UE value of 92.1%. Hence, the engineered nanocage carbon based catalyst demonstrates exceptional ORR performance, exhibiting an excellent half‐wave potential of 0.920 V vs RHE in alkaline media, and a high peak power density of 206.5 mW cm −2 in zinc–air batteries.