Synergistically enhanced single-atomic site Fe by Fe3C@C for boosted oxygen reduction in neutral electrolyte

Highlights: • Fe₃C@C enhanced single-atomic site Fe catalyst (Fe₃C@C-Fe SAS) is fabricated. • The optimized Fe₃C@C-Fe SAS manifests outstanding ORR performance at neutral conditions. • The introduction of Fe₃C@C is verified to optimize the adsorption/desorption of intermediates on Fe SAS. Developing single-atomic site (SAS) catalysts for oxygen reduction reaction (ORR) with superior activities in the renewable-energy initiatives is critical but remains challenging. Herein, exceptional SAS Fe boosted by adjacent graphene-encapsulated Fe₃C nanocrystals (Fe₃C@C-Fe SAS) is constructed for ORR. Because of the strong synergistic effects between SAS Fe and Fe₃C@C nanocrystals, Fe₃C@C-Fe SAS shows robust ORR performance in the neutral electrolyte with the onset potential of 0.99 V and negligible activity loss after 30 k cycles of an accelerated durability test, much better than that of Pt/C catalyst. Notably, the integrated zinc-air battery in the neutral system exhibits an outstanding peak power density of 74.8 mW/cm² and durability over 100 h, representing a state-of-the-art PGM-free ORR catalyst. More importantly, the density functional theory (DFT) calculations shed light on that the introduction of Fe₃C@C nanocrystals is favorable for the activation of O₂ molecules and desorption of OH* on the Fe SAS, resulting in accelerated reaction kinetics and promising ORR activity. Given the explicit structure-performance relationships for Fe₃C@C-Fe SAS, this work provides a new strategy for the design of more advanced energy-based electrocatalysts.