▎ 摘　　要

The development of cost-effective electrocatalysts with high performance for oxygen reduction reaction is the main problem for fuel cells and metal-air batteries. Herein, a novel interconnected hierarchical three-dimensional graphene (3D-HG) is first fabricated by the templated method, where coal tar pitch and CaCO3 were used as carbon precursor and template, respectively. The pyrolysis of CaCO3 could produce CaO and CO2 at 800 degrees C, where the obtained CaO can serve as the template and CO2 can promote the formation of micropores to facilitate the interconnect of the mesopores in 3D-HG. Spinel NiCo2O4 is synthesized on 3D-HG by the hydrothermal method, which is denoted as NiCo2O4/3D-HG. The as-prepared NiCo2O4/3D-HG catalysts retain the hierarchical micro-mesoporous structure of graphene. Benefiting from the mass transport convenience of the hierarchical structure, NiCo2O4/3D-HG exhibits high-performance half-wave potential (0.82 V vs reversible hydrogen electrode (RHE)) better than NiCo2O4/reduced graphene oxide (0.79 V), NiCo2O4/carbon nanotubes (0.73 V), and 20 wt % Pt/C (0.81 V), and shows higher durability than 20 wt % Pt/C. This work proves that NiCo2O4/3D-HG is a cost-effective electrocatalyst for fuel cells or metal-air batteries.