Theoretical Investigation of the Active Sites in N-Doped Graphene Bilayer for the Oxygen Reduction Reaction in Alkaline Media in PEMFCs

Density functional theory was used to investigate the electrocatalytic activity of graphitic, edge, and in-plane defects in pyridinic-N doped on single-layer graphene (SLG) and bilayer graphene (BLG) for the oxygen reduction reaction (ORR) in alkaline media. The N-doped BLG exhibited better ORR activity than the N-doped SLG. Graphitic-N-doped multilayer graphene promoted the 4e^-associative ORR mechanism, where OOH∗ formation was the rate-determining step. The intermediate species of the ORR (OOH∗, O∗, and OH∗) were more strongly bound to the N-doped Bernal BLG structures than to N-doped SLG because of the interlayer covalent φ-phi;bonding between the graphene layers in the former. Bernal stacking of the BLG can improve the stability and ORR activity of graphitic, edge, and in-plane N-defects, where the rate-determining step of the ORR is the same as that in the N-doped graphene monolayer. The overpotential of the BLG with pyridinic-N doped on the edge was 0.570 V, which is nearly identical to that of Pt(111) in alkaline sodium. Therefore, the edge pyridinic-N-doped Bernal BLG may be a promising electrocatalyst for the ORR in polymer electrolyte membrane fuel cells.