Adjacent Axial Ligand Enables Secondary Coordination Effects in Metal-Nitrogen-Carbon Towards Improved Scaling Relation of Oxygen Electrocatalysis

Heterogenous single-atom catalysts (SACs) are reminescent of homogenous catalysts because of similarity of structural motif of active sites, opening a window for applying merits of homogenous catalysts to address issues in hetereogenous catalysis. In heterogeneous oxygen electrocatalysis, the homogeneity of adsorption patterns of reaction intermediates leads to scaling relationships that limit their activities. In contrast, homogeneous catalysts can circumvent such limits by selectively altering the adsorption of intermediates through secondary coordination effects (SCE). This inspired us to explored SCE in metal-nitrogen-carbon (M-N-C), a promising type of oxygen electrocatalysts. First-principles calculations on M-N-C containing two adjacent four-nitrogen-coordinated metal centers show that axial ligand in proximate active sites induces SCE that selectively stabilize OOH intermediate, disrupt scaling relation between oxygen-species, and eventually increase the catalytic activity in oxygen evolution reactions. Additionally, the activity of oxygen reduction reaction of selected M-N-C is also enhanced by such SCE. Our computational work underscored the critical role of SCE in shaping activities of SACs, particularly in breaking stubborn scaling relationships, and demonstrated its potential of leveraging it to tackling challenges in heterogeneous catalysis.