Sm(OH) ₃ -Modified CuO _x -Promoted Electroreduction of CO ₂ -to-C ₂₊ Products through a Proton-Regulated Mechanism

The electrocatalytic reduction of CO 2 to multicarbon (C 2+ ) products can be boosted through regulating the proton supply. This promotes *CO hydrogenation and subsequent C–C coupling through enabling the activation and dissociation of H 2 O. However, this process has often been overlooked, as it may also cause the unfavorable hydrogen evolution reaction. Herein, we present a proton-regulation strategy by introducing Sm(OH) 3 on CuO x as an active site for water dissociation to supply protons, thereby enabling efficient conversion of CO 2 into C 2+ compounds. The constructed 2.4%-Sm(OH) 3 /CuO x exhibits a faradaic efficiency as high as 84.3% for C 2+ production, with an absolute partial current density of up to 627.5 mA cm –2 at −0.77 V versus the reversible hydrogen electrode. Combined experimental results and density functional theory calculations show that the incorporation of appropriate amounts of Sm(OH) 3 enhances the interaction between the interfacial H 2 O and the catalyst, thereby promoting H 2 O dissociation to generate protons. This process facilitates the hydrogenation of *CO intermediates to *CHO and subsequent C–C coupling via *CHO–CHO, thus enhancing the formation of C 2+ products. This work provides insight into the tuning of interfacial H 2 O dissociation for CO 2 conversion.