Unravelling the Effect of Crystal Facet of Derived‐Copper Catalysts on the Electroreduction of Carbon Dioxide under Unified Mass Transport Condition

Abstract Altering the physical structure and chemical property of copper, i.e., particle size, surface morphology, composition or crystal facet, has been demonstrated to be effective in steering the selectivity of products in electrochemical reduction of carbon dioxide. However, these modifications generally result in the change of active surface area, leading to differences in geometric current density and local pH, which are also demonstrated to be the key factors for observed selectivity change. In this work, we deconvolute the effect of mass transport and local pH from the effect of crystal facet by investigating five copper‐based catalysts with identical roughness factor for electrochemical reduction of carbon dioxide in an H‐cell. Interestingly, CuO‐derived catalyst stands out as the best catalyst for C−C coupling. At −1.07 V vs. RHE, the faradaic efficiency of C 2+ product reaches 44.3 %, with a partial current density of −21.6 mA cm −2 . Electrochemical adsorption of *OH reveals that the C 2+ product selectivity of derived‐copper catalysts correlates positively with the ratio of Cu(100)/Cu(110) of five catalysts. Additionally, in situ Raman spectroscopy reveals that the percentage of low‐frequency‐band linear CO (LFB‐CO), which is attributed to the adsorbed *CO on Cu(100) facet, increases with the C−C coupling efficiency.