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

Electrocatalytic CO₂ reduction (CO₂R) to multi-carbon (C₂₊) products in strong acid presents a promising approach to mitigate the CO₂ loss commonly encountered in alkaline and neutral systems. However, this process often suffers from low selectivity for C₂₊ products due to the competing C₁ (e.g., CO and HCOOH) formation and complex C-C coupling kinetics. In this work, we report a CO₂ coverage constraining strategy by diluting CO₂ reactant feed to modulate the intermediate distribution and C-C coupling pathways for an enhanced electrosynthesis of C₂₊ products in strong acid. Lowering the CO₂ feed concentration reduces CO₂ 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 C₁ products. By employing a 20 % CO₂ feed, we achieved a significant improvement in C₂₊ Faradaic efficiency, reaching 68 % at 100 mA cm^-2, approximately 1.7 times higher than the 41 % obtained using pure CO₂. We demonstrated the direct electroreduction of a 30 % CO₂ feed-representative CO₂ concentration of typical industrial flue gases-in a full electrolyzer, achieving a C₂₊ selectivity of 78 % and an energy efficiency of 23 % at 200 mA cm^-2.