Tuning the charge distribution and crystal field of iron single atoms via iron oxide integration for enhanced oxygen reduction reaction in zinc-air batteries

Metal-air batteries face a great challenge in developing efficient and durable low-cost oxygen reduction reaction (ORR) electrocatalysts. Single-atom iron catalysts embedded into nitrogen doped carbon (Fe-N-C) have emerged as attractive materials for potential replacement of Pt in ORR, but their catalytic performance was limited by the symmetrical electronic structure distribution around the single-atom Fe site. Here, we report our findings in significantly enhancing the ORR performance of Fe-N-C by moderate Fe₂O₃ integration via the strong electronic interaction. Remarkably, the optimized catalyst (M−Fe₂O₃/Fe_SA@NC) exhibits excellent activity, durability and good tolerance to methanol, outperforming the benchmark Pt/C catalyst. When M−Fe₂O₃/Fe_SA@NC catalyst was used in a practical zinc-air battery assembly, peak power density of 155 mW cm⁻² and specific capacity of 762 mA h g_Zn⁻¹ were achieved and the battery assembly has shown superior cycling stability over a period of 200 h. More importantly, theoretical studies suggest that the introduction of Fe₂O₃ can evoke the crystal field alteration and electron redistribution on single Fe atoms, which can break the symmetric charge distribution of Fe-N₄ and thereby optimize the corresponding adsorption energy of intermediates to promote the O₂ reduction. This study provides a new pathway to promote the catalytic performance of single-atom catalysts.