N-Doped graphene supported on N-rGO nanosheets as metal-free oxygen reduction reaction electrocatalysts for Zn–air batteries

Abstract

Metal-free electrocatalysts for the oxygen reduction reaction (ORR) are the desired materials for metal–air batteries. Here, low-cost metal-free electrocatalysts of N-doped graphene supported on N-rGO nanosheets (N-graphene@N-rGO) using the composites of copper-based metal–organic frameworks (Cu-BTC) supported on GO (Cu-BTC@GO) for the efficient ORR are reported. The dispersant of GO was introduced into the structure to prevent the aggregation of Cu-BTC, and Cu-BTC could also provide steric hindrance to prevent the GO nanosheets from being stacked. The results indicate that N-graphene@N-rGO had more excellent ORR performance, better durability, and better methanol tolerance than 20 wt% Pt/C in alkaline solution. In addition, the peak power density of a two-electrode zinc–air (Zn–air) battery assembled with N-graphene@N-rGO as the cathode was 139 mW cm⁻², which was higher than that of 20 wt% Pt/C (120 mW cm⁻²). Therefore, N-graphene@N-rGO using the synergy of N-graphene and N-rGO is a promising candidate compared to precious metal-based electrocatalysts for efficient Zn–air batteries.