Nitrogen-doped graphene as catalysts and catalyst supports for oxygen reduction in both acidic and alkaline solutions

Solving slow kinetics of oxygen reduction reaction is critically important for the development of hydrogen fuel cells and direct methanol/ethanol fuel cells. In this study, graphene and nitrogen (N)-doped graphene were synthesized by a solvothermal method and investigated as catalysts as well as catalyst supports for oxygen reduction reactions. In comparison to graphene, N-doped graphene demonstrated higher electrocatalytic activity in both acidic and alkaline solutions. N-doped graphene can act directly as a catalyst to facilitate four-electron oxygen reductions in alkaline solution and two-electron reductions in acidic solution. On the other hand, when used as catalyst supports for Pt and Pt–Ru nanoparticles, N-doped graphene can contribute to four-electron oxygen reductions in acidic solution, yet demonstrate much slower reaction kinetics in alkaline solution. Our findings conclude that N-doped graphene can be developed as an efficient catalyst for oxygen reductions to replace the use of precious Pt catalysts in alkaline solution but not in acidic solution.