Atomically Dispersed Fe–Co Dual Metal Sites\nas Bifunctional Oxygen Electrocatalysts for Rechargeable and Flexible\nZn–Air Batteries

Abstract

Single-metal\nsite catalysts have exhibited highly efficient electrocatalytic\nproperties due to their unique coordination environments and adjustable\nlocal structures for reactant adsorption and electron transfer. They\nhave been widely studied for many electrochemical reactions, including\noxygen reduction reaction (ORR) and oxygen evolution reaction (OER).\nHowever, it remains a significant challenge to realize high-efficiency\nbifunctional catalysis (ORR/OER) with single-metal-type active sites.\nHerein, we report atomically dispersed Fe–Co dual metal sites\n(FeCo–NC) derived from Fe and Co co-doped zeolitic imidazolate\nframeworks (ZIF-8s), aiming to build up multiple active sites for\nbifunctional ORR/OER catalysts. The atomically dispersed FeCo–NC\ncatalyst shows excellent bifunctional catalytic activity in alkaline\nmedia for the ORR (<i>E</i>_1/2 = 0.877 V) and\nthe OER (<i>E</i>_<i>j</i>=10 = 1.579\nV). Moreover, its outstanding stability during the ORR and the OER\nis comparable to noble-metal catalysts (Pt/C and RuO₂).\nThe atomic dispersion state, coordination structure, and the charge\ndensity difference of the dual metal site FeCo–NC were characterized\nand determined using advanced physical characterization and density\nfunctional theory (DFT) calculations. The FeCo–N₆ moieties are likely the main active sites simultaneously for the\nORR and the OER with improved performance relative to the traditional\nsingle Fe and Co site catalysts. We further incorporated the FeCo–NC\ncatalyst into an air electrode for fabricating rechargeable and flexible\nZn–air batteries, generating a superior power density (372\nmW cm^–2) and long-cycle (over 190 h) stability.\nThis work would provide a method to design and synthesize atomically\ndispersed multi-metal site catalysts for advanced electrocatalysis.