Construction of Co/FeCo@Fe(Co)3O4 heterojunction rich in oxygen vacancies derived from metal–organic frameworks using O2 plasma as a high-performance bifunctional catalyst for rechargeable zinc-air batteries

N-doped carbon coated Co/FeCo@Fe(Co)3O4 heterojunction with the periphery composed of FeCo oxide rich in oxygen vacancies and the interior co-composed of Co and FeCo alloy NPs derived from MOFs is successfully constructed by oxygen plasma, which exhibits the most excellent bi-functional electrochemical activity for both ORR and OER. [Display omitted] •N-doped carbon coated Co/FeCo@Fe(Co)3O4 heterojunction is constructed by O2 plasma.•The periphery composed of FeCo oxide and the interior co-composed of Co and FeCo.•It is demonstrated to be a stable and efficient bifunctional catalyst for ORR/OER.•The liquid RZAB possess high power density, specific capacity, super cycle stability.•The flexible ASS-RZAB exhibits a high OCV, good flexibility and stability. Developing high-efficient, good-durability, and low-cost bifunctional non-precious metal catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is urgent and significant for promoting the practical rechargeable zinc-air batteries (RZABs). Herein, N-doped carbon coated Co/FeCo@Fe(Co)3O4 heterojunction rich in oxygen vacancies derived from metal–organic frameworks (MOFs) is successfully constructed by O2 plasma treatment. The phase transition of Co/FeCo to FeCo oxide (Fe3O4/Co3O4) mainly occurs on the surface of nanoparticles (NPs) during the O2 plasma treatment, which can form rich oxygen vacancies simultaneously. The fabricated catalyst P-Co3Fe1/NC-700-10 with optimal O2 plasma treatment time of 10 min can reduce the potential gap between the OER and ORR to 760 mV, which is much lower than commercial 20% Pt/C + RuO2 (910 mV). Density functional theory (DFT) calculation indicates that the synergistic coupling between Co/FeCo alloy NPs and FeCo oxide layer can promote the ORR/OER performance. Both liquid electrolyte RZAB and flexible all-solid-state RZAB using P-Co3Fe1/NC-700-10 as the air–cathode catalyst display high power density, specific capacity and excellent stability. This work provides an effective idea for the development of high performance bifunctional electrocatalyst and the application of RZABs.