FeNi alloy embedded in three-dimensional nitrogen-doped porous carbon as bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries

Abstract

Iron‑nickel (FeNi) alloy is one of the efficient bifunctional oxygen electrocatalysts for zinc-air batteries (ZABs). However, FeNi alloy nanoparticles prepared by traditional synthesis strategies are easy to agglomerate and have non-uniform sizes, which is not conducive to the improvement of catalytic activity and stability. Here, we have successfully encapsulated two different kinds of nitrogen-rich metal phthalocyanines (MPcs) in situ doping in zeolitic imidazolate framework (ZIF-8) homogeneously by the “double solvents” method. The ligand nitrogen and macrocyclic structure of MPcs encapsulated in ZIF-8 not only helps metal dispersion and enhances the metal-ligand‑nitrogen (M-Nx) structure, but also enhances the graphitisation of three-dimensional (3D) porous carbon after pyrolysis. Thus, a FeNi alloy uniformly embedded in 3D nitrogen-doped porous carbon materials (FeNi@NC) was constructed in the subsequent pyrolysis process and used as an efficient bifunctional oxygen reduction/evolution (ORR/OER) electrocatalyst for rechargeable ZABs. Impressively, the FeNi@NC catalyst carries high half-wave potential (0.850 V) in ORR and the low overpotential (291 mV) in OER, significantly better than Pt/C (0.830 V) and RuO2 (307 mV), respectively. In addition, the rechargeable ZAB assembled with FeNi@NC air cathode has a specific capacity of 649 mW cm−2 and shows no significant degradation after 240 h of charging and discharging cycles. This study provides a new design idea for the manufacture of carbon-supported non-noble metal alloy catalysts with bifunctional oxygen catalytic activity, and verifies the feasibility of regulating the composition of non-noble metals to construct a rechargeable ZABs with excellent performance.