Graphene oxide anchored Fe, Co-codoped ZIF-8 derived FeCo-based N-doped carbon composite as a highly efficient bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

Metal-nitrogen-carbon (M–N–C) catalysts are promising alternatives to precious metal-based bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Zn-air batteries (ZABs). Herein, FeCo@nitrogen doped carbon nanotube/nitrogen doped reduced graphene oxide (FeCo@NCNT/N-rGO) catalyst with unique 3D heterostructure was synthesized through one-step pyrolysis of FeCo-ZIF-8 precursor anchored on graphene oxide (FeCo-ZIF-8/GO). Benefiting from the coupling of FeCo dual-metal sites with nitrogen-doped carbon substrates, the FeCo@NCNT/N-rGO catalyst achieved extraordinary bifunctional oxygen electrocatalytic activity, exhibiting a high ORR half-wave potential (E 1/2 ) of 0.881 V (vs. RHE), which was superior to the Pt/C catalyst (0.838 V), and OER overpotential of 343 mV at 10 mA cm −2 , merely inferior to RuO 2 by 33 mV. The resulting ΔE (defined as E j=10  − E 1/2 ) reaches an impressively low value of 0.69 V, highlighting its superior reversible oxygen electrocatalytic performance. Meanwhile, achieving a high-power density of 240 mW cm −2 and open circuit voltage (OCV) of 1.488 V in ZAB applications, superior to that of Pt/C + RuO 2 in ZAB (1.447 V; 143 mW cm −2 ). Flexible solid-state ZAB with FeCo@NCNT/N-rGO achieves 1.416 V OCV and 47.4 mW cm −2 power density, remaining stable even when bent 180°. This study guides design of dual-site non-precious metal bifunctional oxygen catalysts.