Developing innovative, easy-to-manufacture, and non-Pt-group-metal (non-PGM) electrocatalysts is essential for the highly efficient oxygen reduction reaction (ORR). Herein, we report a self-sacrificing post-synthetic strategy to synthesize highly loaded Fe-isolated single atoms anchored on the hierarchical porous N,S co-doped carbon matrix (Fe-SAs/S,N-C/rGO). The optimized Fe-SAs/S,N-C/rGO exhibits excellent ORR activity in the pH-universal range with half-wave potentials of 0.89, 0.80, and 0.60 V in alkaline, acidic, and neutral media, comparable to the commercial Pt/C (0.85, 0.81, and 0.64 V, respectively). The homemade liquid Zn-air battery (ZAB) with Fe-SAs/S,N-C/rGO as the cathode catalyst displays an open-circuit voltage (OCV) of ~ 1.61 V, discharging specific capacity of 817.23 mAh·g⁻¹, and long-term durability of ~ 1865 cycles, outperforming those of the device with commercial Pt/C+RuO₂ (1.49 V, 657.32 mAh·g⁻¹, and ~ 120 cycles, respectively). Intriguingly, the corresponding flexible solid-state ZAB delivers satisfactory OCV, peak power density, foldability, and cycling stability at room temperature, as well as adaptability at a low temperature of −10 °C. Besides, density functional theory (DFT) calculation reveals that the atomic FeN₃S moieties in Fe-SAs/S,N-C/rGO can cause charge redistribution and lower the binding strength of oxygen-containing intermediates, resulting in accelerated ORR kinetics and optimized catalytic activity. This work provides insights into experimental and theoretical guidance towards non-PGM electrocatalysts for efficient energy conversion.

Developing innovative and efficient non-precious-metal-group (non-PMG) electrocatalysts is crucial for the wide use of zinc-air batteries (ZABs). Herein, a single-atom catalyst (termed as Fe-N-C/rGO SAC) with unique five N-coordinated Fe (Fe-N₅) centers is prepared by pyrolyzing the composite of zeolitic-imidazolate-frameworks-8 (ZIF-8) and graphene oxide (GO). Specifically, the individual Fe site is stabilized by four equatorial and one axial N atoms donated by the N-doped carbon matrix and imidazole ring, respectively, thus forming an asymmetric electron depletion zone over the metal center, which can effectively promote the generation of reactive intermediates and accelerate the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes for ZABs. The rechargeable liquid ZAB with Fe-N-C/rGO catalyst exhibits an extremely high energy density (928.25 Wh·kg⁻¹), a remarkable peak power density (107.12 mW·cm⁻²), and a long cycle life (400 h). Additionally, the corresponding flexible solid-state ZAB displays superior foldability and remarkable cycling stability. This work provides both experimental and theoretical guidance for rational design of non-PMG electrocatalyst-driven ZABs.