A DFT study on the relationship between local microstructure and oxygen reduction reaction activity over Fe-N4 graphene

Recently, the catalytic sites of Fe-N-4 have been studied widely due to their unique physicochemical characteristics. However, the effect of oxygen substitution for N on oxygen reduction reaction (ORR) activity is unclear. In this work, the Fe-(N/C)(x)O-y (x + y = 4) graphene were selected as the prototypical system and were explored by density functional theory (DFT) calculations. Our results reveal that the activity of Fe-N2O2 and Fe-NO3 ORR performance are better than Fe-N-4 under the acidic and alkaline conditions, respectively. Further investigations indicate that there may be a linear relationship between the difference of magnetic moment and the change of Gibbs free energy. Our calculations demonstrate that the ORR performance may benefit from low magnetic moments of the metal center for *OOH and *O intermediates but high magnetic moments of the metal center for *OH intermediate. The local microstructure could modify effectively the magnetic property of the catalytic center and this provides new inspiration for the experiment to obtain better ORR performance.