Anomalous C-C Coupling on Under-Coordinated Cu (111): A Case Study of Cu Nanopyramids for CO₂ Reduction Reaction by Molecular Modelling

Converting CO₂ to high value-added C₂ hydrocarbons by CO₂ reduction reaction attracted attention due to higher energy density, readiness for transportation, and established utilization infrastructure. Herein, it was demonstrated that tailoring the copper catalyst morphology by forming nanopyramids offers alternative routes to promote C₂ production. Using density functional theory calculations, five polycrystalline Cu nanopyramids with various orientations, shapes, and exposing facets were investigated. Three investigated nanopyramids favored the C₂ production to different extents due to anomalous C-C coupling behaviors. The underlying reason for such C-C coupling was the pyramidal effect on under-coordinated Cu (111) surface from the nanopyramids. The pyramidal effect includes improved *CO adsorption, geometrically preferable sites for C-C coupling, and enhanced electron transfer. Based on these results, a C₂ active site screening principle was developed: an extended "square" principle, which can serve as a new morphology design rule for efficient catalyst development.