Easy synthesis of N-doped graphene by milling exfoliation with electrocatalytic activity towards the Oxygen Reduction Reaction (ORR)

We report a novel process to synthesize graphene (G) catalyst by mechanical milling using graphite flakes as the precursor. G sample has been doped ex situ with hydrazine as nitrogen source via solvothermal procedure to obtain the GD1 catalyst. In a second approach, the GD2 sample has been synthesized doping G with uric acid as nitrogen precursor in situ, i.e., during the milling step. Doping with nitrogen increases the ID/IG Raman spectra ratios of GD1 and GD2 to 1.52 and 1.12, respectively, higher than 1.02 of G. XPS analysis shows that Pyridinic, Amine, Pyrrolic, Graphitic and Oxidized nitrogen are formed at GD1, while only Pyrrolic is present at GD2. Evaluation of catalytic activity for the ORR in 0.5 mol L−1 KOH shows an increase in onset potential (Eonset) of the ORR at GD1, compared to G and GD2. GD1 also generated a higher current density (j) at 0.83 V than G and GD2. The results show that mechanical milling is an efficient method to synthesize G. Even though, the doping can still be improved to form more Nitrogen that promotes the ORR, specifically Pyridinic N and Graphitic N.