Construction of porous N-doped graphene layer for efficient oxygen reduction reaction

Graphitic carbon materials have shown great potential for use as high-performance catalysts for electrochemical reactions and devices. In this work, we developed a simple and versatile method for synthesis of porous N-doped graphene layers (NGS) by high-temperature treatment of chitosan film deposited on the graphitic carbon nitride (g-C₃N₄) nanosheets. In the sandwiched chitosan/g-C₃N₄/chitosan structure, the g-C₃N₄ nanosheet served as a substrate for chitosan film. The pyrolysis of this substrate, g-C₃N₄ nanosheet, prevented the severe agglomeration of as-carbonized chitosan sheets and resulted the porous structure. The BET surface area, micropore volume, nitrogen content and graphitic level of result sample highly depended on the heat-treatment temperature. The NGS synthesized at 1000 °C (NGS-1000) exhibited an ultrahigh specific surface area (1183 m² g⁻¹) and high nitrogen content (4.12%). Importantly, NGS-1000 exhibited a higher limiting current density (5.8 mA cm⁻²) and a greater stability than the commercial Pt/C electrocatalyst in alkaline media for oxygen reduction reaction (ORR). Such excellent electrocatalytic performance can be explained by a balanced combination of appropriate nitrogen doping level, the degree of graphitization, porous structure, and high specific surface area.