Density Functional Theory Calculation of Zn and N Codoped Graphene for Oxygen Reduction and Evolution Reactions

The highly efficient and low-cost electrocatalysts are of great importance for energy conversion systems such as fuel cells, metal-air batteries, and water electrolyzers. Here, the activities of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in zinc and nitrogen codoped graphene with different zinc-nitrogen (Zn-N) coordination numbers and configurations are studied by density functional theory (DFT) calculations. The calculation results show that both Zn-N coordination numbers and structure configurations affect the activities of ORR and OER on ZnN(x)sites. Among all the calculated structures, ZnN4-pyridine shows the lowest ORR overpotential of 0.61 V, whereas ZnN4-pyrrole and ZnN4-edge show lower OER overpotentials of 0.73 and 0.63 V, respectively. However, the other low N coordination structures of ZnNx-pyridine/pyrrole/edge (x= 1/0/1-3) demonstrate poor activities. The electronic structure reveals that the O-p orbital shows moderate hybridization strength with the N-p and Zn-d orbitals in O adsorbed ZnN(4)systems thus facilitates the electrocatalytic reactions. The findings shed light on the rational design of bifunctional electrocatalysts for energy storage and conversion.