Dual modulation of coordination asymmetry and curvature unlocks record-level Zn-air battery performance with Fe-N-C single-atom catalysts

Abstract

The coordination environment of single-atom catalysts (SACs) plays a pivotal role in determining their electronic structure and catalytic performance. Conventional planar Fe-N4 motifs, however, often bind oxygen intermediates too strongly, limiting their activity in oxygen electrocatalysis. Here, we report a symmetry-breaking strategy coupled with nanoscale surface curvature engineering to tailor the electronic and spatial configuration of isolated Fe sites anchored on a sulfur/nitrogen co-doped highly concave carbon polyhedron (Fe-N4S1/SNhcC). This dual-scale structural design delivers outstanding bifunctional activity for the oxygen reduction and evolution reactions (ORR/OER), achieving a high half-wave potential of 0.933 V and a small ORR/OER potential gap (ΔE) of 0.695 V. Density functional theory calculations reveal that the asymmetric Fe-N4S1 coordination, modulated by surface curvature, weakens *OH binding and lowers the energy barrier for ORR. Finite element simulations further show that the local electric field generated by the concave surface enhances the adsorption of O2 and OH-, thereby accelerating reaction kinetics. When applied as a cathode in quasi-solid-state Zn-air batteries, Fe-N4S1/SNhcC demonstrates exceptional performance across a wide temperature range (-60 to 80 °C), including a high peak power density of 181 mW cm-2 and extended cycling stability of 210/120/80 h at 20/50/100 mA cm-2, respectively. Notably, it delivers a discharge capacity of 1.56 Ah and a cycling lifespan exceeding 2000 h at -40 °C and 2 mA cm-2. This work highlights the importance of dual-scale structural modulation in SACs and opens new avenues for rechargeable Zn-air batteries operating under extreme conditions.