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.