Coordination environments tune the activity of oxygen catalysis on single atom catalysts: A computational study

Designing highly efficient bifunctional electrocatalysts for oxygen reduction and evolution reaction (ORR/OER) is extremely important for developing regenerative fuel cells and metal-air batteries. Single-atom catalysts (SACs) have gained considerable attention in recent years because of their maximum atom utilization efficiency and tunable coordination environments. Herein, through density functional theory (DFT) calculations, we systematically explored the ORR/OER performances of nitrogen-coordinated transition metal carbon materials (TM-N_x-C (TM = Mn, Fe, Co, Ni, Cu, Pd, and Pt; x = 3, 4)) through tailoring the coordination environment. Our results demonstrate that compared to conventional tetra-coordinated (TM-N₄-C) catalysts, the asymmetric tri-coordinated (TM-N₃-C) catalysts exhibit stronger adsorption capacity of catalytic intermediates. Among them, Ni-N₃-C possesses optimal adsorption energy and the lowest overpotential of 0.29 and 0.28 V for ORR and OER, respectively, making it a highly efficient bifunctional catalyst for oxygen catalysis. Furthermore, we find this enhanced effect stems from the additional orbital interaction between newly uncoordinated d-orbitals and p-orbitals of oxygenated species, which is evidently testified via the change of d-band center and integral crystal orbital Hamilton population (ICOHP). This work not only provides a potential bifunctional oxygen catalyst, but also enriches the knowledge of coordination engineering for tailoring the activity of SACs, which may pave the way to design and discover more promising bifunctional electrocatalysts for oxygen catalysis.