A comparison of single and double Co sites incorporated in N-doped graphene for the oxygen reduction reaction

•DFT calculations are used to investigate the ORR on Co-N/C catalysts.•Double sites with Co in the same carbon sheet and adjacent sheets are studied.•Dissociation of O2 to 2O has large free energy barriers (>1 eV) on Co double sites.•The occurrence of Co double sites facilitates OOH dissociation to O and OH.•Co double sites can increase ORR activity and suppress H2O2 formation.•We analyze the sensitivity of results to the chosen solvent model.