Exploring the nitrogen species of nitrogen doped graphene as electrocatalysts for oxygen reduction reaction in Al–air batteries

• There is no linear connection between the nitrogen content and catalytic activity.
• The Al–air battery with mass ratio of 1:200 N-graphene displays better discharge performance.
• The DFT method was used to calculate the adsorption energy of nitrogen species.
• The graphitic N is proved to play a positive role in catalyzing ORR.

The relationship of nitrogen species and catalytic activity of nitrogen doped graphene for oxygen reduction reaction (ORR) is extensively studied but is still inconclusive. In this paper, the specific nitrogen types in N-graphene are controlled by regulating the mass ratio of graphene oxide (GO) and urea. The detection of groups on the surface of N-graphene is carried out by X-ray photoelectron spectroscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. The catalytic activity of N-graphene catalysts with different nitrogen configurations is evaluated by cyclic voltammograms (CV), rotating disk electrode (RDE), and electrochemical impedance spectroscopy (EIS) measurements in O2-saturated 0.1 M KOH electrolyte. It is found that the N-graphene with the mass ratio of 1:200 (containing graphitic N configuration) shows better oxygen reduction catalytic activity than that of other mass ratio (without graphitic N configuration) catalysts. Furthermore, the Al−air battery with the mass ratio of 1:200 N-graphene cathode displays higher open circuit voltage and energy density. Density functional theory (DFT) quantum chemical calculations are used to investigate the influence of different nitrogen species on adsorption energy of oxygen atoms. The calculated results indicate graphitic N is more conducive for the adsorption of oxygen atoms.