Phosphorus-doped graphene nanosheets as efficient metal-free oxygen reduction electrocatalysts

Metal-free phosphorus-doped graphene nanosheets (P-TRG) with large surface area (496.67 m(2) g(-1)) and relatively high P-doping level (1.16 at.%) were successfully prepared by thermal annealing a homogenous mixture of graphene oxide and 1-butyl-3-methlyimidazolium hexafluorophosphate under argon atmosphere. It was found that the P atoms were substitutionally incorporated into the carbon framework and were partially oxidized, which created new active sites for the oxygen reduction reaction (ORR). Accordingly, the ORR catalytic performance of the P-doped graphene was demonstrated to be better than or at least comparable to that of the benchmark Pt/C catalyst.