Structure-activity relationship of Cu-based catalysts for the highly efficient CO₂ electrochemical reduction reaction

Electrocatalytic carbon dioxide reduction (CO₂RR) is a relatively feasible method to reduce the atmospheric concentration of CO₂. Although a series of metal-based catalysts have gained interest for CO₂RR, understanding the structure-activity relationship for Cu-based catalysts remains a great challenge. Herein, three Cu-based catalysts with different sizes and compositions (Cu@CNTs, Cu₄@CNTs, and CuNi₃@CNTs) were designed to explore this relationship by density functional theory (DFT). The calculation results show a higher degree of CO₂ molecule activation on CuNi₃@CNTs compared to that on Cu@CNTs and Cu₄@CNTs. The methane (CH₄) molecule is produced on both Cu@CNTs and CuNi₃@CNTs, while carbon monoxide (CO) is synthesized on Cu₄@CNTs. The Cu@CNTs showed higher activity for CH₄ production with a low overpotential value of 0.36 V compared to CuNi₃@CNTs (0.60 V), with *CHO formation considered the potential-determining step (PDS). The overpotential value was only 0.02 V for *CO formation on the Cu₄@CNTs, and *COOH formation was the PDS. The limiting potential difference analysis with the hydrogen evolution reaction (HER) indicated that the Cu@CNTs exhibited the highest selectivity of CH₄ among the three catalysts. Therefore, the sizes and compositions of Cu-based catalysts greatly influence CO₂RR activity and selectivity. This study provides an innovative insight into the theoretical explanation of the origin of the size and composition effects to inform the design of highly efficient electrocatalysts.