A self-assemble N-doped graphene and N-doped carbon nanoparticles integrated composite has been prepared by a multi-step acid etching plus annealing method. The formation of N-doped graphene is likely based on a “decomposition and recrystallization” mechanism without the use of any metallic catalyst. The as-prepared integrated composite exhibits efficient catalytic activity for four-electron oxygen reduction reaction.

Abstract

N-doped carbon-based materials have been regarded as promising alternatives to Pt-based electrocatalysts for the four-electron (4e⁻) oxygen reduction reaction (ORR), which is an important electrochemical reaction for the polymer electrolyte fuel cells. Here, we report a N-doped graphene and N-doped carbon nanoparticles integrated composite electrocatalyst by a multi-step acid etching plus annealing method. Despite the low N-doping level, the material exhibits efficient 4e⁻ ORR activity with an onset potential of 0.932 V, a half-wave potential of 0.814 V, and a limiting current density of 5.3 mA cm⁻² in 0.1 M KOH solution. We demonstrate that the promoted 4e⁻ ORR activity is attributed to the special 2D–0D integrated structure for exposing massive active sites, the favorable porous structure facilitating the H₂O transfer dynamics, and the high content of oxygen-containing C−O−C species and the increased intrinsic carbon defects for additional active sites. A “decomposition and recrystallization” mechanism is proposed for the formation of N-doped graphene.