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

Abstract

Density functional theory was used to investigatethe electrocatalytic activity of graphitic, edge, and in-plane defectsin pyridinic-N doped on single-layer graphene (SLG) and bilayergraphene (BLG) for the oxygen reduction reaction (ORR) inalkaline media. The N-doped BLG exhibited better ORR activitythan the N-doped SLG. Graphitic-N-doped multilayer graphenepromoted the 4e-associative ORR mechanism, where OOH*formation was the rate-determining step. The intermediate speciesof the ORR (OOH*,O*, and OH*) were more strongly bound tothe N-doped Bernal BLG structures than to N-doped SLG becauseof the interlayer covalent pi-pi bonding between the graphenelayers in the former. Bernal stacking of the BLG can improve thestability 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 ofthe 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.