Dual-site oxygen reduction reaction mechanism on CoN4 and CoN2 embedded graphene: Theoretical insights

Abstract As one of the potential candidates of electrocatalysts, non-precious transition metal and nitrogen embedded graphene has attracted extensive attention in recent years. Deep understanding of the oxygen reduction reaction (ORR) mechanism including the specific active sites and reaction pathways will contribute to the further enhancement of their catalytic activity. In this work, density functional study is conducted on the ORR process of CoN 2 and CoN 4 embedded graphene in acid medium. The calculated formation energy shows that both CoN 2 and CoN 4 embedded graphenes are thermodynamically stable configurations. On the CoN 4 site, the reaction pathway to form HOOH is the most favorable pathway. However, CoN 4 site does not promote complete ORR and HOOH is the final product. Meanwhile, for CoN 2 embedded graphene, the reaction pathway of HOOH dissociation is also the most favorable pathway and the energy barrier is 0.58 eV in the rate-determining step. This implies that CoN 2 site serves as the second site for the complete ORR on the CoN x embedded graphene. Therefore, the HOOH formed on the CoN 4 site can be dissociated on the CoN 2 site, leading to a dual-site 2 × 2e − ORR mechanism. Finally, the effect of different electrode potentials on the ORR is discussed.