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 (E_1/2) 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 E_1/2 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.

Oxygen reduction reaction (ORR) is crucial for Zn-air batteries, while also serves as a core electrochemical process in oxygen depolarized cathodes (ODCs) for chlor-alkali electrolysis. The lack of cost-effective, highly active ORR electrocatalysts with superior kinetics hinders progress in this field. Herein, we report the Fe/Ni dual single-atomic sites anchored by commercial carbon black (Fe/Ni-N/CB) using rigid ligand confined and high-temperature shock (HTS) strategy in less than 0.5 s. Theoretical calculation reveals that single-atomic Fe is the real active site. Single-atomic Fe and Ni species in Fe/Ni-N/CB synergistically accelerate the kinetics of ORR by reducing the energy barrier of the rate-determining step. A large half-wave potential (E_1/2) of 0.907 V is achieved in 0.1 M KOH aqueous solution. The assembled aqueous Zn-air battery (A-ZAB) with Fe/Ni-N/CB cathode presents remarkable charge–discharge cycling stability for over 650 h without voltage gap degradation. The quasi-solid-state Zn-air battery (QSS-ZAB) exhibits excellent reversibility over a 150-h operation at 0.5 mA·cm⁻² with negligible energy conversion efficiency recession. Impressively, Fe/Ni-N/CB||RuO₂ chlor-alkali flow cell exhibits a low cell voltage of 1.60 V at a large current density of 300 mA·cm⁻² at 80 °C, and demonstrates exceptional durability with 7% current density decay over 150 h of continuous operation at 100 mA·cm⁻². Fe/Ni-N/CB||RuO₂ achieves near-ideal caustic current efficiency (~ 97.2%) at the current density of 300 mA·cm⁻². This work provides a rapid and economical synthesis technique for the synthesis of catalysts at the atomic scale while demonstrating significant potential for application in energy-saving chlor-alkali electrolyzer.

Single atom catalysts (SACs) featuring Fe-N₄ active sites anchored on carbon supports exhibit exceptional electrocatalytic performance in oxygen reduction reactions (ORR). Herein, a rigid ligand confined strategy was used to synthesize edge-anchored Fe-N₄ active sites with geometric distortion on mesoporous-dominated carbon spheres (Fe-N-MESs). Furthermore, in situ Fourier transform infrared spectroscopy (FTIR) demonstrates that Fe-N-MESs weaken the O–O band, inhibiting the formation of H₂O₂. The density functional theory (DFT) calculations reveal that the exceptional ORR activity stems from optimized oxygen intermediate adsorption free energy and reduced OH^* desorption energy barrier. Electrochemical measurements verify the remarkable ORR activity of Fe-N-MESs, demonstrating a half-wave potential of 0.90 V and excellent stability, with approximately 94% of the initial current density after 50 h of operation. When used as the air cathode in aqueous Zn-air batteries, Fe-N-MESs display a large open circuit voltage of 1.53 V and an extra-long stability of 1500 h. Moreover, Fe-N-MESs exhibit a remarkable open circuit voltage of 1.50 V and an impressive peak power density up to 260.4 mW·cm⁻² in quasi-solid-state Zn-air batteries. This work provides valuable insights into the boosted ORR origin, while offering a novel and economical synthesis technique for SACs applicable to other electrocatalytic reactions.

Dual atom catalysts (DACs), are promising electrocatalysts for oxygen reduction reaction (ORR) on account of the potential dual-atom active sites for the optimized adsorption of catalytic intermediates and the lower reaction energy barriers. Herein, spatial confinement strategy to fabricate DACs with well-defined Fe, Co dual-atom active site is proposed by implanting zeolitic imidazolate frameworks inside the pores of highly porous carbon nanospheres (Fe/Co-SAs-N_x-PCNSs). The atomically dispersed dual-atom active sites facilitate the adsorption/desorption of intermediates. Furthermore, the spatial confinement effect protects metal atoms aggregating. Benefiting from the rich accessible dual-atom active sites and boosted mass transport, we achieve remarkable ORR performance with half-wave potential up to 0.91 and 0.8 V (vs. reversible hydrogen electrode (RHE)), and long-term stability up to 10 h in both alkaline and acidic electrolytes. The remarkably enhanced ORR catalytic property of our as-developed DACs is in the rank of excellence for 1%. The as-developed rechargeable Zn-air battery (ZAB) with Fe/Co-SAs-N_x-PCNSs air cathode delivers ultrahigh power density of 216 mW·cm⁻², outstanding specific capacity of 813 mAh·g⁻¹, and promising cycling operation durability over 160 h. The flexible Zn-air battery also exhibits excellent specific capacity, cycling stability, and flexibility performance. This work opens up a new pathway for the multiscale design of efficient electrocatalysts with atomically dispersed multiple active sites.