Inverse opal structured Fe single-atom catalyst enables highly stable rechargeable Zn–air batteries and energy saving chlor-alkali electrolysis

Abstract Developing active and durable air cathodes for oxygen reduction reaction (ORR) is pivotal for rechargeable aqueous Zn–air battery (A-ZAB) and chlor-alkali electrolysis. Fe-N-C single-atom catalysts have shown great promise, yet the critical role of the carbon support structure remains underexplored. Herein, we report the Fe single-atom on hierarchically ordered porous carbon (Fe-N-HOC) with an inverse opal structure. Fe-N-HOC features high-density Fe–N4 sites and delivers highly active ORR performance in alkaline media, attaining substantially enhanced half-wave potential (E1/2) of 0.90 V. Density functional theory (DFT) calculations manifest that the curved configuration Fe–N4 enhances electron transfer, weakens the binding strength of oxygen intermediates, and reduces the energy barrier of *OH desorption significantly by 0.79 eV relative to planar analogues, boosting ORR kinetics. Consequently, Fe-N-HOC delivers excellent durability, with only 8 mV loss in E1/2 after 50,000 cycles. In practical applications, A-ZAB with Fe-N-HOC achieves remarkable cycling for 1600 h at 5 mA·cm−2. Fe-N-HOC-based quasi-solid-state ZAB (QSS-ZAB) also exhibits large peak power density of 216.7 mW·cm−2 and extended cycle life (> 130 h) across the current densities of 0.5–2.0 mA·cm−2. Furthermore, in chlor-alkali electrolysis, the Fe-N-HOC||RuO2 system operates at 1.62 V for large current density of 300 mA·cm−2 with minimal performance decay. This work presents a multi-dimensional modification strategy encompassing morphology control, element doping, and electronic tuning, providing crucial guidance for the development of efficient catalysts in energy conversion and storage systems.