▎ 摘　　要

The development of highly efficient and low cost electrocatalysts for the oxygen reduction reaction (ORR) is crucial for metal-air batteries and fuel cells. Herein, an acid-assisted approach has been developed to prepare nitrogen-doped graphene electrocatalysts via the co-precipitation of graphene oxide (GO) and melamine in the presence of various inorganic acids (e.g., HNO3, H2SO4, and H3PO4), and a subsequent pyrolysis process. When used as an electrocatalyst, the nitrogen doped graphene prepared in the presence of nitric acid exhibited the best catalytic activity towards the ORR by a four-electron pathway with the largest current density (similar to 5.5 mA cm(-2)) and the highest onset potential (similar to 0.90 V vs. RHE) in comparison with the samples prepared in the presence of sulfuric acid and phosphate acid. Being a corrosive and oxidizing acid, nitric acid is likely to promote the formation of surface defects and pyridinic nitrogen under the thermal treatment, thus improving the electrocatalytic activity. More importantly, Zn-air batteries were fabricated by using the as-prepared electrocatalysts in the air electrode, exhibiting high power density and good long-term stability. This facile acid-assisted approach provides a new strategy to synthesize low-cost yet highly efficient heteroatom doped carbon electrocatalysts for the ORR.