Template growth of nitrogen-doped mesoporous graphene on metal oxides and its use as a metal-free bifunctional electrocatalyst for oxygen reduction and evolution reactions

Abstract

Metal-free electrocatalyst is an emerging energy material to replace precious metal for effective oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in a working electrochemical energy conversion device. Developing an effective bifunctional catalyst with abundant highly active sites and full exposure to reactants is strongly considered. Herein a nitrogen-doped mesoporous graphene framework (NMGF) was proposed with intrinsic N/O heteroatoms and abundant topological defects for metal-free ORR/OER. The NMGF was fabricated by direct chemical vapor deposition on MgO template. The as-obtained NMGF exhibited high porosity with a large specific surface area of 1440m2g−1 as well as a high electrical conductivity of 57.0Scm−1. This unique structure is demonstrated to possess several advantages, including plentiful active centers due to defects and heteroatoms, improved utilization efficiency by very high electrochemically active surface area and hydrophilic surface, facilitated ion diffusion through interconnected pores and smooth electron transportation in the highly conductive 3D framework, thereby leading to superior ORR and OER bifunctional activity. The ORR half-wave potential was 0.714V, and the potential to reach 10.0mAcm−2 OER current density was 1.664V with the potential gap of 0.95V. This bifunctional performance was better than routine precious metal-based catalysts (e.g. Pt/C and IrO2) for oxygen redox reaction.