Multiscale engineering of triple-phase catalytic architecture: integrating atomic Fe–Nx sites, Fe/Fe3C nanoclusters and Ni(OH)2 nanocrystals on S,N-doped carbon for rechargeable Zn–air batteries

Abstract

The development of high-performance bifunctional oxygen electrocatalysts remains a critical challenge for rechargeable zinc–air batteries (ZABs), primarily due to the intrinsically sluggish kinetics of both the oxygen reduction (ORR) and evolution reactions (OER). Herein, we report a strategically designed composite electrocatalyst through multiscale architectural engineering, comprising atomically dispersed Fe–N_x sites coupled with Fe/Fe₃C nanoclusters on S,N-doped hierarchical porous carbon (FeN/SNC) and surface-anchored Ni(OH)₂ nanocrystals. Experimental and theoretical analyses reveal that sulfur dopants optimize the electronic configuration of Fe–N_x sites, while Fe/Fe₃C nanoclusters establish conductive Fe–S–C networks for rapid charge transfer. The hybrid catalyst (Ni(OH)₂/FeN/SNC) achieves excellent bifunctional activity with a potential gap of only 0.665 V (0.855 V for ORR half-wave potential and 1.52 V for OER at 10 mA cm⁻²), outperforming Pt/C + RuO₂ benchmarks. When applied in ZABs, it delivers exceptional performance in terms of a power density of 145 mW cm⁻², a specific capacity of 831 mAh g⁻¹, an energy efficiency of 60.9%, and remarkable stability (>200 h cycling). Notably, the material maintains superior performance in flexible quasi-solid-state configurations. This work establishes a new paradigm for designing multifunctional electrocatalysts through controlled integration of complementary active species at multiple scales.