Design principles of nitrogen-doped graphene nanoribbons as highly effective bifunctional catalysts for Li-O2 batteries

Li-O-2 batteries are promising candidates in fields demanding high capacities like electric vehicles due to their superior theoretical energy density in contrast to lithium-ion batteries. However, the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the carbonous cathode of Li-O-2 batteries are kinetically sluggish. Herein, we explore the electrocatalytic activities, electronic structures, and the underlying catalytic mechanisms of nitrogen-doped graphene nanoribbons (N-GNRs) by density functional theory calculations. The edge effect of zigzag GNRs and the doping effect of nitrogen atoms alter the electronic structure of GNRs and significantly reduce the energy barrier of the two-electron ORR/OER. The overpotential of the GNRs can reach 0.025 V, demonstrating better catalytic activity than the noble metals Ag(111) and Au(100). Four-electron preferential sites also exist in N-GNRs, usually located at the center of the nanoribbons and far away from the nitrogen atom.