Controlling the Activity and Selectivity of Cu Catalysts toward Industrially Relevant Ethanol Electrosynthesis via High-Index Step Density Engineering

Electrochemical CO₂ reduction reaction on Cu catalysts can generate high-value multicarbon (C₂₊) products, making it a significant research area of growing commercial interest. However, the production rate of ethanol remains low owing to the trade-off between the activity and selectivity of Cu catalysts. Here, we develop a defect-rich Cu catalyst with abundant high-index step sites by chemically etching commercially available Cu nanoparticles. This catalyst exhibits a high Faradaic efficiency of ∼50% and a partial current density of ∼416 mA cm^-2 for ethanol production. Furthermore, it shows good stability at a high total current density of ∼800 mA cm^-2, without obvious decay in ethanol selectivity. Control experiments indicate that the impressive ethanol selectivity is closely associated with the high density of high-index steps present on the defect-rich Cu catalyst. <i>In situ</i> Raman spectroscopy and density functional theory calculations further verify that the optimal high-index step sites enable balanced adsorption of *CO, *OH, and *H, and facilitate the hydrogenation of *CHCOH to *CHCHOH, thereby improving ethanol selectivity. This work underscores the importance of step density control for steering the reaction pathway and selectivity toward ethanol.