Catalyst-free, tunable doping content of graphitic-N in arc-discharged graphene via gas and solid nitrogen sources and their formation mechanisms

Facile, cost-effective, and catalyst-free synthesis of graphitic-nitrogen (graphitic-N) doping in arc-discharged graphene has been achieved via a gas (N₂) nitrogen source. The N-doped graphene sheets are mainly of 2–5 layers. According to the growth mechanisms of the cathode-part (deposit) graphene during the arcing process, N₂ exhibits a varying capability to form the graphitic-N doping. When N₂ acts as the nitrogen source, the cathode-part deposit is mainly consist of graphitic-N graphene sheets. The content of the nitrogen atom is calculated to be ~ 2.88 at%. However, when melamine is used as a nitrogen source, the atomic percentage (AP) of graphitic-N doping is almost equal to the pyridinic- and pyrrolic-N doping in the cathode-part deposit. Based on the findings, a new growth mechanism of graphitic-N doping in arc graphene is rationally proposed. The electrochemical impedance spectroscopy (EIS) results suggest that the graphite-N doping on the graphene can decrease the electron transfer resistance (Rct) and have better electrical conductivity than the normal N-doped graphene (N-NDG).