NiN/FeN dual sites engineered by Fe 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 NiN/FeN dual sites and adjacent Fe nanoclusters (NiN-Fe-FeN@PCF) was synthesized. The optimization of the local arrangement and electronic structure of the FeN/NiN sites by the neighboring Fe nanoclusters conferred NiN-Fe-FeN@PCF with excellent bifunctional ORR/OER activity and stability that were superior to those of DACs comprising only NiN/FeN dual sites and commercialized Pt/C and RuO reference catalysts. A liquid ZAB with a NiN-Fe-FeN@PCF cathode achieved outstanding cycling stability for over 900 h. The Fe clusters effectively induced geometric structure distortion and electron redistribution of the NiN and FeN sites, optimizing the interactions between the FeN/NiN 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.