A pH-universal ORR catalyst with atomic Fe-heteroatom (N, S) sites for high-performance Zn-air batteries

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.