Manipulating the selectivity-determining step in post-C–C coupling is crucial for enhancing C₂ product specificity during electrocatalytic CO₂ reduction, complementing efforts to boost rate-determining step kinetics. Here we highlight the role of single-site noble metal dopants on Cu surfaces in influencing C–O bond dissociation in an oxygen-bound selectivity-determining intermediate, steering post-C–C coupling toward ethylene versus ethanol. Integrating theoretical and experimental analyses, we demonstrate that the oxygen binding strength of the Cu surface controls the favorability of C–O bond scission, thus tuning the selectivity ratio of ethylene-to-ethanol. The Rh-doped Cu catalyst with optimal oxygen binding energy achieves a Faradaic efficiency toward ethylene of 61.2% and an ethylene-to-ethanol Faradaic efficiency ratio of 4.51 at –0.66 V versus RHE (reversible hydrogen electrode). Integrating control of both rate-determining and selectivity-determining steps further raises ethylene Faradaic efficiency to 68.8% at 1.47 A cm⁻² in a tandem electrode. Our insights guide the rational design of Cu-based catalysts for selective CO₂ electroreduction to a single C₂ product.

操纵后C-C偶联中的选择性决定步骤对于增强电催化CO _{2还原过程中C 2}产物的特异性至关重要，补充了促进速率决定步骤动力学的努力。在这里，我们强调铜表面上的单点贵金属掺杂剂在影响氧结合选择性决定中间体中的 C-O 键解离中的作用，从而引导 C-C 偶联后向乙烯与乙醇的方向发展。综合理论和实验分析，我们证明铜表面的氧结合强度控制着C-O键断裂的有利程度，从而调节乙烯与乙醇的选择性比。具有最佳氧结合能的铑掺杂铜催化剂在 –0.66 V 与 RHE（可逆氢电极）相比时，对乙烯的法拉第效率为 61.2%，乙烯与乙醇的法拉第效率比为 4.51。速率决定和选择性决定步骤的集成控制进一步将串联电极中1.47 A cm ^{-2的乙烯法拉第效率提高至68.8%。}_{我们的见解指导合理设计用于选择性CO 2}电还原为单一C ₂产品的铜基催化剂。