Structural rule of heteroatom-modified single-atom catalysts for the CO2 electroreduction reaction

The carbon dioxide electroreduction reaction (CO2RR) has emerged as a viable strategy to address pressing energy and environmental challenges. Single-atom catalysts (SACs) are of particular interest for the CO2RR due to their maximized atom utilization. The incorporation of heteroatoms as ligands is a common strategy to modify the geometric and electronic structures of metal centers to enhance performance. Here, we employed density functional theory study to investigate nitrogen-coordinated SACs with various heteroatom ligands and elucidated the structural rule of SACs on the CO2RR. The results show that the stability of SACs exhibits a volcano-shaped trend as a function of the ligand radius, with both excessively large and small radius compromising stability, and the planar structural SACs exhibit relatively better stabilities than the raised ones. Although the raised structural SACs have better ability to activate CO2 for the tip effect, they also hinder CO desorption and facilitate H+ adsorption, leading to relatively poor CO2RR activity and selectivity (vs. the HER). In contrast, planar-structured SACs generally show better activity and CO2RR selectivity, where promoting the CO2 activation step is necessary. This work provides fundamental insights into the structure-dependence of SACs and offers guidance for designing SACs for the CO2RR or other reactions.