Tailoring the morphology of nanocrystals is a promising way to enhance their catalytic performance. In most previous shape-controlled synthesis strategies, surfactants are inevitable due to their capability to stabilize different facets. However, the adsorbed surfactants block the intrinsic active sites of the nanocrystals, reducing their catalytic performance. For now, strategies to control the morphology without surfactants are still limited but necessary. Herein, a facile surfactant-free synthesis method is developed to regulate the morphology of Cu 2 O nanocrystals (e.g., solid nanocube, concave nanocube, cubic framework, branching nanocube, branching concave nanocube, and branching cubic framework) to enhance the electrocatalytic performance for the conversion of CO to n-propanol. Specifically, the Cu 2 O branching cubic framework (BCF-Cu 2 O), which is difficult to fabricate using previous surfactant-free methods, is fabricated by combining the concentration depletion effect and the oxidation etching process. More significantly, the BCF-Cu 2 Oderived catalyst (BCF) presents the highest n-propanol current density (−0.85 mA cm −2 ) at −0.45 V versus the reversible hydrogen electrode (V RHE ), which is fivefold higher than that of the surfactant-coated Cu 2 O nanocube-derived catalyst (SFC, −0.17 mA cm −2 ). In terms of the n-propanol Faradaic efficiency in CO electroreduction, that of the BCF exhibits a 41% increase at −0.45 V RHE as compared with SFC. The high catalytic activity of the BCF that results from the clean surface and the coexistence of Cu(100) and Cu(110) in the lattice is well-supported by density functional theory calculations. Thus, this work presents an important paradigm for the facile fabrication of surface-clean nanocrystals with an enhanced application performance.

We have employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) and density functional theory (DFT) calculations to study the CO reduction reaction (CORR) on Cu single-crystal surfaces under various conditions. Coadsorbed and structure-/potential-dependent surface species, including *CO, CuÀ O ad , and CuÀ OH ad , were identified using electrochemical spectroscopy and isotope labeling. The relative abundance of *OH follows a "volcano" trend with applied potentials in aqueous solutions, which is yet absent in absolute alcoholic solutions. Combined with DFT calculations, we propose that the surface H 2 O can serve as a strong proton donor for the first protonation step in both the C 1 and C 2 pathways of CORR at various applied potentials in alkaline electrolytes, leaving adsorbed *OH on the surface. This work provides fresh insights into the initial protonation steps and identity of key interfacial intermediates formed during CORR on Cu surfaces.

We have employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) and density functional theory (DFT) calculations to study the CO reduction reaction (CORR) on Cu single-crystal surfaces under various conditions. Coadsorbed and structure-/potential-dependent surface species, including *CO, CuÀ O ad , and CuÀ OH ad , were identified using electrochemical spectroscopy and isotope labeling. The relative abundance of *OH follows a "volcano" trend with applied potentials in aqueous solutions, which is yet absent in absolute alcoholic solutions. Combined with DFT calculations, we propose that the surface H 2 O can serve as a strong proton donor for the first protonation step in both the C 1 and C 2 pathways of CORR at various applied potentials in alkaline electrolytes, leaving adsorbed *OH on the surface. This work provides fresh insights into the initial protonation steps and identity of key interfacial intermediates formed during CORR on Cu surfaces.

Mechanistic studies on CO 2 and CO electroreduction (CO 2 R and COR, respectively) usually focus on detecting reaction intermediates and elucidating the first C−C coupling step. Interestingly, the structural sensitivity of the adsorption of CO 2 or CO has been largely overlooked, although their adsorption is the first step of the electrolysis and thus directly impacts their activities and selectivities. Herein, we first show, through density functional theory calculations and microkinetic considerations, that CO 2 adsorption on copper (Cu) is largely enhanced by sites with low coordination numbers (cn), while the adsorption strength of CO is fairly constant across surfaces with different cn. This implies that the yields of CO 2 R products would be more enhanced on highly undercoordinated sites, while the yields of COR products would be similar even on sites with different coordination. To test this prediction, we prepared two Cu catalysts with different overall roughness/cn and performed CO 2 R and COR on them from −0.60 to −0.85 V vs reversible hydrogen electrode. On the more undercoordinated Cu catalyst, CO 2 reduced with an average Faradaic efficiency (FE) that is 13 percentage points higher compared to that of the more coordinated Cu. In contrast, CO reduced with similar FEs on both catalysts (average difference of 2 percentage points). Our complementing experimental and computational observations challenge the general view that CO is always a better feedstock than CO 2 for producing multi-carbon products and illustrate the importance of combining suitable feedstocks and Cu sites to optimize the production of high-value chemicals.