N-doped graphene catalysts with high nitrogen concentration for the oxygen reduction reaction

Nitrogen doped reduced graphene oxide (NrGO) catalysts and composites of these with carbon nitride (CN) with nitrogen content as high as 19.8 wt% and 35.8 wt%, respectively, have been synthesized by thermal annealing of multilayer graphene oxide and urea at different temperatures. Nitrogen has been effectively introduced as a mix of pyridinic, pyrrolic, pyridonic and quaternary bonding configurations into the carbon lattice of graphene upon removal of CN phase over 650 degrees C. The electrocatalytic activity towards oxygen reduction reaction (ORR) in 0.1 M NaOH has been investigated. NrGO catalysts with less nitrogen content show better performance than composites. NrGO produced at 800 degrees C presents the best activity with half-wave potential of 0.76 V vs. RHE and a mean number of electrons of 3.7, which are close to a commercial Pt/C catalyst. This study concludes that a high concentration of nitrogen atoms in multilayer reduced graphene oxide does not necessarily produce a highly active electrocatalyst, suggesting that carbon in the neighbourhood of nitrogen atoms are the active sites for ORR in alkaline medium.