Edge‐Rich Graphene Nanospheres with Ultra‐High Nitrogen Loading Metal‐Free Electrocatalysts for Boosted Oxygen Reduction

Abstract

Nitrogen (N) doping in graphene‐based materials has been demonstrated as an effective strategy in constructing active sites of metal‐free catalysts for oxygen reduction reaction (ORR). The practical applications of metal‐free electrocatalysts in metal‐air batteries or fuel cells, nevertheless, have been hampered by their unsatisfactory catalytic performance due to insufficient catalytic active sites. In this work, a novel N‐rich graphene nanospheres (NGNs) have been achieved by adopting an edge engineering strategy through annealing the mixture of graphitic carbon nitride (g‐C3N4) and edge‐rich graphene nanospheres (GNs) composed of graphene nanoflakes. Benefiting from the exposure of edge defects in the GNs, the N loading surprisingly achieved as high as 14.01 at%. The half‐wave potential and limiting current density of the synthesized NGNs‐900 catalyst can reach 0.872 V and 4.25 mA cm−2, respectively, which are superior to that of the commercial Pt/C. Based on the experimental and theoretical results, the synergistic effect of graphitic‐N and pyridinic‐N in NGNs catalysts has been distinguished as the origin of the boosted ORR performance. This work proposes a facile synthesis strategy to optimize the N‐doped carbon‐based catalysts for ORR, which have great potential to replace noble‐metal catalysts.