▎ 摘　　要

The oxygen reduction reaction (ORR) is a critical step in the operation of fuel cells. The exploration of efficient, low cost and durable non-precious ORR catalysts, to replace the rare and expensive Pt-based catalysts, is promising towards the large-scale commercialization of fuel cells. Here, we report the fabrication of high-quality graphene (GP) with controllable layers, using a simple, versatile and cost-effective electrochemical exfoliation method. Our systematic studies revealed that the graphite precursor, electrolyte temperature, and pyrolysis conditions largely affect the number of layers and quality of the graphene, which consequently has a significant effect on its ORR performance. The optimized graphene sample was subsequently heat-treated in the NH3 atmosphere to obtain the nitrogen-doped graphene (N-GP). As a metal-free electrocatalyst, N-GP exhibit much enhanced ORR activity than GP, and comparable ORR activity to the state-of-the-art Pt/C catalyst. Moreover, it also shows better stability than Pt/C catalyst in alkaline solution.