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Electrocatalytic carbon monoxide reduction has been previously reported to yield a range of carbonaceous products including alcohols, hydrocarbons and carboxylic acids. However, esters, an important family of organic compounds, have not been formed. Herein, we report the electrosynthesis of C3 to C6 acetate esters (H3C−(C=O)−O−R) from carbon monoxide using copper catalysts in a membrane electrode assembly cell. Ethyl acetate and propyl acetate could be produced with an unprecedented total Faradaic efficiency (FE) of ∼22 % and with a current density of up to −55 mA cm−2, alongside minor quantities of methyl acetate and butyl acetate. The esters are produced via the addition reaction of ethenone (H2C=C=O) and alcohols produced during CO reduction. We show that the near water‐free reaction conditions and the high local pH play key roles in the formation of the esters. [ABSTRACT FROM AUTHOR]

The electrochemical CO2 reduction reaction (CO2RR) using renewable energies is a promising route toward global carbon neutrality. Recently, the use of copper catalysts and CO feedstocks, instead of CO2, has been shown to enhance the selectivity toward multicarbon products, leading to increased efforts in developing tandem electrocatalytic systems. State‐of‐the‐art CO2‐to‐CO electrocatalysts are mainly based on noble metals such as silver and gold. Earth‐abundant zinc, in contrast, displays poorer selectivity and activity. Herein, the use of porous dendritic oxidederived zinc (OD‐Zn) catalysts for CO2RR is reported. These catalysts can reduce CO2 to CO with a maximum Faradaic efficiency of 86% at −0.95 V versus reversible hydrogen electrode (RHE) and partial current density of −266 mA cm–2 at −1.00 V vs RHE. OD‐Zn is further found to have a higher amount of undercoordinated sites and exhibits higher CO2RR activity and CO selectivity than electrodeposited Zn metal. While oxygen vacancies have been previously implicated as active sites, detailed experiments and density functional theory calculations show that Zn sites with a high degree of undercoordination provide even higher activity, in view of their nearly optimal *COOH adsorption energies. These findings showcase Zn‐Oderived particles with plentiful undercoordinated sites as cost‐effective electrocatalysts for CO production. [ABSTRACT FROM AUTHOR]

The electrochemical CO and CO2 reduction reactions (CORR and CO2RR) using copper catalysts and renewable electricity hold promise as a carbon‐neutral route to produce commodity chemicals and fuels. However, the exact mechanisms and structure sensitivity of Cu electrodes toward C2 products are still under debate. Herein, we investigate ethylene oxide reduction (EOR) as a proxy to the late stages of CORR to ethylene, and the results are compared to those of acetaldehyde reduction to ethanol. Density functional theory (DFT) calculations show that ethylene oxide undergoes ring opening before exclusively reducing to ethylene via *OH formation. Based on generalized coordination numbers (CN), a selectivity map for the late stages of CORR and CO2RR shows that sites with moderate coordination (5.9 < CN < 7.5) are efficient for ethylene production, with pristine Cu(100) being more active than defective surfaces such as Cu(311). In contrast, kinks and edges are more active for ethanol production, while (111) terraces are relatively inert. [ABSTRACT FROM AUTHOR]

Abstract: The selective electroreduction of CO2 to formate (or formic acid) is of great interest in the field of renewable‐energy utilization. In this work, we designed a sulfur‐doped Cu2O‐derived Cu catalyst and showed that the presence of sulfur can tune the selectivity of Cu significantly from the production of various CO2 reduction products to almost exclusively formate. Sulfur is doped into the Cu catalysts by dipping the Cu substrates into ammonium polysulfide solutions. Catalyst films with the highest sulfur content of 2.7 at % showed the largest formate current density (j HCOO - ) of −13.9 mA cm−2 at −0.9 V versus the reversible hydrogen electrode (RHE), which is approximately 46 times larger than that previously reported for Cu(110) surfaces. At −0.8 V versus RHE, the faradaic efficiency of formate was maintained at approximately 75 % for 12 h of continuous electrolysis. Through the analysis of the evolution of the j HCOO - and j H 2 values with the sulfur content, we show that sulfur doping increases formate production and suppresses the hydrogen evolution reaction. Ag–S and Cu–Se catalysts did not exhibit any significant enhancement towards the reduction of CO2 to formate. This demonstrates clearly that sulfur and copper acted synergistically to promote the selective formation of formate. A hypothesis about the role of sulfur is proposed and discussed. [ABSTRACT FROM AUTHOR]

CO electroreduction (COR), powered by renewable electricity, shows promise for producing green chemicals at the industrial scale. Here, we aim to understand why amongst C 2 products, acetate is formed with relatively greater selectivity on Cu catalysts mounted in flow cells, as compared to in H-cells. We attribute this to improved CO transport in flow cells, which increases local pH and *CO coverage (θ * CO). The effect of local pH was verified through COR in different electrolytes, which shows a significant increase in the Faradaic efficiency (FE) of acetate as local pH rose. Higher CO concentrations in flow cells under similar local pH also substantially increased the FE acetate , as compared to FE ethylene and FE ethanol. This suggests that acetate formation is most sensitive to θ * CO. DFT calculations emphasize the importance of θ * CO in favoring acetate formation from the *CHCO intermediate, and reveals the role of lateral interactions in the production of C 2 molecules. [Display omitted] • CO electroreduction on copper catalysts produces more acetate in flow cells than in H-cells. • Flow cells favor acetate production by providing high local pH and *CO coverage. • Low *CO coverage favors *CHCO reduction to *CHCHO, leading to ethylene and ethanol. • High *CO coverage favors *CHCO reduction to *CH 2 CO (g) , leading to acetate. [ABSTRACT FROM AUTHOR]

• CO 2 reduction to CH 4 on Cu occurs via two different potential-dependent pathways. • Deactivation of Cu catalysts may be a consequence of a *COH-based coking pathway. • *COH is more stable than *CHO at 0 V vs RHE, but its symmetry factor is smaller. • A shift to a *CHO-based, non-coking pathway occurs at more negative potentials. • Rising *CHO formation's symmetry factor may sizably lower the CO 2 RR overpotential. The deactivation of copper electrodes is a serious problem that can affect the scalability and deployment of CO 2 electrolyzers. The effect is generally attributed to the cathodic deposition of Fe and Zn impurities from the electrolyte. Herein, an experimental-theoretical study shows the existence of potential- and facet-dependent pathways for CO 2 reduction to CH 4 on Cu. The small-overpotential pathway deactivates the electrodes, while the large-overpotential pathway does not. Theoretical modeling traces the origin of the deactivation to *COH and *CHO, the two *CO hydrogenation products. *COH, which reduces to *C (precursor to coke), is more stable than *CHO around the equilibrium potential, but its symmetry factor is smaller. Hence, the *COH-based coking pathway opens first until the potential is negative enough for the *CHO-based pathway to dominate. This highlights the often-neglected role of symmetry factors in electrocatalysis design and suggests that small increases in *CHO's symmetry factor can mitigate Cu deactivation. [ABSTRACT FROM AUTHOR]