▎ 摘　　要

In order to reveal oxygen reduction reaction (ORR) mechanisms of N- and N/S-codoped graphene quantum dots, we utilize density functional theory to investigate their electrocatalytic activities and pathways toward four-electron and two-electron reduction reactions. The calculation results indicate that the introduction of a S atom can change the state of N doping and result in asymmetric spin and charge density. The free energy diagram of reaction pathways reveals that the introduction of a S atom improves their electrocatalytic performance in the ORR Our computational results also indicate that pyridinic N doping sites exhibit higher electrocatalytic activity than graphitic N sites since pyridinic N doping sites exhibit higher thermodynamic limiting potential for the ORR than graphitic N doping sites. Also, N/S codoping exhibits enhanced activity toward ORRs compared with the N-doped counterparts. The findings above will provide useful guidance for the rational design of N/S-codoped carbon materials for ORR electrocatalysis and understanding catalytic mechanisms.