Constraining CO₂ Coverage on Copper Promotes CO₂ Electroreduction to Multi‐carbon Products in Strong Acid

Abstract Electrocatalytic CO 2 reduction (CO 2 R) to multi‐carbon (C 2+ ) products in strong acid presents a promising approach to mitigate the CO 2 loss commonly encountered in alkaline and neutral systems. However, this process often suffers from low selectivity for C 2+ products due to the competing C 1 (e.g., CO and HCOOH) formation and complex C−C coupling kinetics. In this work, we report a CO 2 coverage constraining strategy by diluting CO 2 reactant feed to modulate the intermediate distribution and C−C coupling pathways for an enhanced electrosynthesis of C 2+ products in strong acid. Lowering the CO 2 feed concentration reduces CO 2 coverage on copper catalyst, enriching the surface coverage and optimizing the adsorption configuration of the key CO intermediate for C−C coupling. This approach efficiently suppresses the formation of undesired C 1 products. By employing a 20 % CO 2 feed, we achieved a significant improvement in C 2+ Faradaic efficiency, reaching 68 % at 100 mA cm −2 , approximately 1.7 times higher than the 41 % obtained using pure CO 2 . We demonstrated the direct electroreduction of a 30 % CO 2 feed—representative CO 2 concentration of typical industrial flue gases—in a full electrolyzer, achieving a C 2+ selectivity of 78 % and an energy efficiency of 23 % at 200 mA cm −2 .