Copper can efficiently electro‐catalyze carbon dioxide reduction to C2+ products (C2H4, C2H5OH, n‐propanol). However, the correlation between the activity and active sites remains ambiguous, impeding further improvements in their performance. The facet effect of copper crystals to promote CO adsorption and C−C coupling and consequently yield a superior selectivity for C2+ products is described. We achieve a high Faradaic efficiency (FE) of 87 % and a large partial current density of 217 mA cm−2 toward C2+ products on Cu(OH)2‐D at only −0.54 V versus the reversible hydrogen electrode in a flow‐cell electrolyzer. With further coupled to a Si solar cell, record‐high solar conversion efficiencies of 4.47 % and 6.4 % are achieved for C2H4 and C2+ products, respectively. This study provides an in‐depth understanding of the selective formation of C2+ products on Cu and paves the way for the practical application of electrocatalytic or solar‐driven CO2 reduction.

Cu-based electrocatalysts facilitate CO 2 electrochemical reduction (CO 2 ER) to produce multi-carbon products. However, the roles of Cu 0 and Cu + and the mechanistic understanding remain elusive. This paper describes the controllable construction of Cu 0 -Cu + sites derived from the welldispersed cupric oxide particles supported on copper phyllosilicate lamella to enhance CO 2 ER performance. 20 % Cu/ CuSiO 3 shows the superior CO 2 ER performance with 51.8 % C 2 H 4 Faraday efficiency at À1.1 V vs reversible hydrogen electrode during the 6 hour test. In situ attenuated total reflection infrared spectra and density functional theory (DFT) calculations were employed to elucidate the reaction mechanism. The enhancement in CO 2 ER activity is mainly attributed to the synergism of Cu 0 -Cu + pairs: Cu 0 activates CO 2 and facilitates the following electron transfers; Cu + strengthens *CO adsorption to further boost CÀC coupling. We provide a strategy to rationally design Cu-based catalysts with viable valence states to boost CO 2 ER.