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.