An efficient electrocatalyst toward oxygen reduction reaction: State-of-the-art of hierarchical porous nanostructure of Mn3O4 supported on three-dimensional graphene

•Mn3O4/3DHG catalyst was prepared by hydrothermal method using 3DHG as support.•3DHG with hierarchical porous structure possessed more defects and expose more active sites.•Mn3O4/3DHG with hierarchical porous structure was beneficial to enhance mass transfer.•Mn3O4/3DHG demonstrated superior ORR activity and higher durability than Pt/C.