Oxygen reduction reaction mechanism of N-doped graphene nanoribbons

The oxygen reduction reaction (ORR) activity for the N-doped graphene nanoribbons with armchair (N-ACGNRs) and zigzag (N-ZZGNRs) edges has been investigated using first-principles calculations within the density functional theory. The values of the maximum electrode potential (U-Max) for each doping site and reaction site of N-ACGNRs and N-ZZGNRs have been calculated. The selectivity for ORR with respect to two pathways, the direct four-electron (4e(-)) and the two-electron (2e(-)) pathways, has also been examined. The U-Max for N-ZZGNR has a parity dependence with regard to the nitrogen doping site in the vicinity of the zigzag edge: For the even-numbered doping sites from the edge, the values of U-Max are larger than 0 V, while for the odd-numbered ones, those become negative. On the other hand, the U-Max for N-ACGNR becomes positive for each doping and reaction site. The reaction selectivity for the 4e(-) pathway appears only in the vicinity of the edges for N-ACGNRs and N-ZZGNRs, because the reaction intermediates adsorb stably on the edge C or pi*-localized C atom adjacent to the doped N atom. Published by the AVS.