Revealing Real Active Sites in Intricate Grain Boundaries Assemblies on Electroreduction of CO₂ to C₂₊ Products

Abstract Although intricate structural assemblies contribute to enhancing the activity of electrocatalytic CO 2 reduction (ECR) to C 2+ products, blindly coupling multiple design strategies may not yield the expected results, and even inhibit the activity of intrinsic catalytic sites. Therefore, elucidating the promoting or inhibitory effects of each design strategy on the CO 2 ‐to‐C 2+ conversion to clarify the real active sites and dynamic oxidation processes is of paramount importance. Here, commonly used grain boundaries (GBs), oxidation states, and alloying strategies are focused on, constructing four different types of catalysts structures: original Cu GBs, oxygen‐enriched grain boundary oxidation (GBO), Ag‐enriched GBO, and Cu/Ag GBs. Multiple operando characterizations reveal that GBs and GBO strengthen the resistance of the oxidative Cu species to the electrochemical reduction. The in situ generated strongly oxidative hydroxyl radicals alter the local reaction environment on the catalyst surface, inducing and stabilizing oxidative Cu δ+ species. Catalytic activity comparisons indicate that the oxidation state of Cu plays a decisive role in the CO 2 ‐to‐C 2+ conversion, and the nanoalloy effect tends to favor the CH 4 production in intricate GBs assemblies. Theoretical calculations suggest that weak CO adsorption on GBO structures facilitates hydrogenation, promoting C–C coupling toward C 2+ products.