Co0.7Fe0.3 NPs confined in yolk–shell N-doped carbon: engineering multi-beaded fibers as an efficient bifunctional electrocatalyst for Zn–air batteries

Abstract

The development of bifunctional catalysts with a delicate structure, high efficiency, and good durability for the oxygen evolution reaction (ORR) and oxygen evolution reaction (OER) is crucial to renewable Zn–air batteries. In this work, Co_0.7Fe_0.3 alloy nanoparticles (NPs) confined in N-doped carbon with a yolk–shell structure in multi-beaded fibers were prepared as a bifunctional electrocatalyst. The confinement structure was composed of an N-doped graphitized carbon shell and a core formed by numerous Co_0.7Fe_0.3 NPs, and was evenly threaded into a one-dimensional fiber. Moreover, this distinctive hierarchical structure featured abundant mesopores, a high BET surface area of 743.8 m² g⁻¹, good electronic conductivity, and uniformly distributed Co_0.7Fe_0.3/Co(Fe)–N_x coupling active sites. Therefore, the experimentally optimized Co_0.7Fe_0.3@NC_2:1-800 showed excellent OER performance (overpotential reached 314 mV at 10 mA cm⁻²) that far exceeded RuO₂ (353 mV), and good ORR catalytic performance (half-wave potential of 0.827 V) comparable to Pt/C (0.818 V). Impressively, the Co_0.7Fe_0.3@NC_2:1-800 Zn–air battery delivered a higher open circuit voltage of 1.449 V, large power density of 85.7 mW cm⁻², and outstanding charge–discharge cycling stability compared with the commercial RuO₂ + 20 wt% Pt/C catalyst. This work provides new ideas for the structural design of electrocatalysts and energy conversion systems.