NiN4/FeN4 dual sites engineered by Fe5 clusters on porous flexible carbon fibers for promoting oxygen reduction and evolution

Dual-atom catalysts (DACs) are promising bifunctional electrocatalysts for the oxygen reduction/evolution reaction (ORR/OER) because of their tunable electronic structures and multiple types of active metal sites. However, achieving high catalyst activity and long-term durability towards both the ORR and OER when used in zinc-air batteries (ZABs) remain challenging. Herein, a flexible porous carbon fiber catalyst embedded with atomically scattered NiN₄/FeN₄ dual sites and adjacent Fe₅ nanoclusters (NiN₄-Fe₅-FeN₄@PCF) was synthesized. The optimization of the local arrangement and electronic structure of the FeN₄/NiN₄ sites by the neighboring Fe nanoclusters conferred NiN₄-Fe₅-FeN₄@PCF with excellent bifunctional ORR/OER activity and stability that were superior to those of DACs comprising only NiN₄/FeN₄ dual sites and commercialized Pt/C and RuO₂ reference catalysts. A liquid ZAB with a NiN₄-Fe₅-FeN₄@PCF cathode achieved outstanding cycling stability for over 900 h. The Fe₅ clusters effectively induced geometric structure distortion and electron redistribution of the NiN₄ and FeN₄ sites, optimizing the interactions between the FeN₄/NiN₄ sites and oxygen intermediates; thus, the energy barriers for the potential-determining steps reduced. This study opens an emerging pathway for the synthesis of self-supporting atomic catalysts and provides in-depth insight into the synergistic effects between DACs and metal nanoclusters.