The selective electroreduction of carbon dioxide to C2 compounds (ethylene and ethanol) on copper­(I) oxide films has been investigated at various electrochemical potentials. Aqueous 0.1 M KHCO3 was used as electrolyte. A remarkable finding is that the faradic yields of ethylene and ethanol can be systematically tuned by changing the thickness of the deposited overlayers. Films 1.7–3.6 μm thick exhibited the best selectivity for these C2 compounds at −0.99 V vs RHE, with faradic efficiencies (FE) of 34–39% for ethylene and 9–16% for ethanol. Less than 1% methane was formed. A high C2H4/CH4 products’ ratio of up to ∼100 could be achieved. Scanning electron microscopy, X-ray diffraction, and in situ Raman spectroscopy revealed that the Cu2O films reduced rapidly and remained as metallic Cu0 particles during the CO2 reduction. The selectivity trends exhibited by the catalysts during CO2 reduction in phosphate buffer, and KHCO3 electrolytes suggest that an increase in local pH at the surface of the electrode is not the only factor in enhancing the formation of C2 products. An optimized surface population of edges and steps on the catalyst is also necessary to facilitate the dissociation of CO2 and the dimerization of the pertinent CH x O intermediates to ethylene and ethanol.

The electrochemical reduction of carbon dioxide (CO 2 ) to ethanol (C 2 H 5 OH) and ethylene (C 2 H 4 ) using renewable electricity is a viable method for the production of these commercially vital chemicals. Copper (Cu) and its oxides are by far the most effective electrocatalysts for this purpose. However, the formation of ethanol using these catalysts is generally less favored in comparison to that of ethylene. In this work, we demonstrate that the selectivity of CO 2 reduction toward ethanol could be tuned by introducing a cocatalyst to generate an in situ source of mobile CO reactant. Cu-based oxides with different amounts of Zn dopants (Cu, Cu 10 Zn, Cu 4 Zn, and Cu 2 Zn) were prepared and used as catalysts under ambient pressure in aqueous 0.1 M KHCO 3 electrolyte. By varying the amount of Zn in the bimetallic catalysts, we found that the selectivity of ethanol versus ethylene production, defined by the ratio of their Faradaic efficiencies (FE ethanol /FE ethylene ), could be tuned by a factor of up to ∼12.5. Ethanol formation was maximized on Cu 4 Zn at −1.05 V vs RHE, with a remarkable Faradaic efficiency and current density of 29.1% and −8.2 mA/cm 2 , respectively. The Cu 4 Zn catalyst was also catalytically stable for the production of ethanol for at least 5 h. The importance of Zn as a CO-producing site was demonstrated by performing CO 2 reduction on Cu−Ni and Cu−Ag bimetallic catalysts. Operando Raman spectroscopy revealed that the as-deposited Cu-based oxide films were reduced to the metallic state during CO 2 reduction, after which only signals belonging to CO adsorbed on Cu sites were recorded. This showed that the reduction of CO 2 probably occurred on metallic sites rather than on metal oxides. A two-site mechanism to rationalize the selective reduction of CO 2 to ethanol is proposed and discussed.

Passivation of interfacial defects serves as an effective means to realize highly efficient and stable perovskite solar cells (PSCs). However, most molecular modulators currently used to mitigate such defects form poorly conductive aggregates at the perovskite interface with the charge collection layer, impeding the extraction of photogenerated charge carriers. Here, a judiciously engineered passivator, 4‐tert‐butyl‐benzylammonium iodide (tBBAI), is introduced, whose bulky tert‐butyl groups prevent the unwanted aggregation by steric repulsion. It is found that simple surface treatment with tBBAI significantly accelerates the charge extraction from the perovskite into the spiro‐OMeTAD hole‐transporter, while retarding the nonradiative charge carrier recombination. This boosts the power conversion efficiency (PCE) of the PSC from ≈20% to 23.5% reducing the hysteresis to barely detectable levels. Importantly, the tBBAI treatment raises the fill factor from 0.75 to the very high value of 0.82, which concurs with a decrease in the ideality factor from 1.72 to 1.34, confirming the suppression of radiation‐less carrier recombination. The tert‐butyl group also provides a hydrophobic umbrella protecting the perovskite film from attack by ambient moisture. As a result, the PSCs show excellent operational stability retaining over 95% of their initial PCE after 500 h full‐sun illumination under maximum‐power‐point tracking under continuous simulated solar irradiation.

Developing efficient systems for the conversion of carbon dioxide to valuable chemicals using solar power is critical for mitigating climate change and ascertaining the world’s future supply of clean fuels. Here, we introduce a mesoscopic cathode consisting of Cu nanowires decorated with Ag islands, by the reduction of Ag-covered Cu2O nanowires prepared via galvanic replacement reaction. This catalyst enables CO2 reduction to ethylene and other C2+ products with a faradaic efficiency of 76%. Operando Raman spectroscopy reveals intermediate formation of CO at Ag sites which undergo subsequent spillover and hydrogenation on the Cu nanowires. Our Cu–Ag bimetallic design enables a ∼95% efficient spillover of intermediates from Ag to Cu, delivering an improved activity toward the formation of ethylene and other C2+ products. We also demonstrate a solar to ethylene conversion efficiency of 4.2% for the photoelectrochemical CO2 reduction using water as electron and proton donor, and solar power together with perovskite photovoltaics to drive the uphill reaction.

Stable and selective electrochemical reduction of carbon dioxide to ethylene was achieved using copper mesocrystal catalysts in 0.1 M KHCO 3 . The Cu mesocrystal catalysts were facilely derived by the in situ reduction of a thin CuCl film during the first 200 seconds of the CO 2 electroreduction process.At −0.99 V vs. RHE, the Faradaic efficiency of ethylene formation using these Cu mesocrystals was 18× larger than that of methane and forms up to 81% of the total carbonaceous products. Control CO 2 reduction experiments show that this selectivity towards C 2 H 4 formation could not be replicated by using regular copper nanoparticles formed by pulse electrodeposition. High resolution transmission electron microscopy reveals the presence of both (100) Cu facets and atomic steps in the Cu mesocrystals which we assign as active sites in catalyzing the reduction of CO 2 to C 2 H 4 . CO adsorption measurements suggest that the remarkable C 2 H 4 selectivity could be attributed to the greater propensity of CO adsorption on Cu mesocrystals than on other types of Cu surfaces. The Cu mesocrystals remained active and selective towards C 2 H 4 formation for longer than six hours. This is an important and industrially relevant feature missing from many reported Cu-based CO 2 reduction catalysts.

The reduction of carbon dioxide (CO2) to n-propanol (CH3CH2CH2OH) using renewable electricity is a potentially sustainable route to the production of this valuable engine fuel. In this study, we report that agglomerates of ∼15 nm sized copper nanocrystals exhibited unprecedented catalytic activity for this electrochemical reaction in aqueous 0.1 M KHCO3. The onset potential for the formation of n-propanol was 200-300 mV more positive than for an electropolished Cu surface or Cu(0) nanoparticles. At -0.95 V (vs RHE), n-propanol was formed on the Cu nanocrystals with a high current density (jn-propanol) of -1.74 mA/cm(2), which is ∼25× larger than that found on Cu(0) nanoparticles at the same applied potential. The Cu nanocrystals were also catalytically stable for at least 6 h, and only 14% deactivation was observed after 12 h of CO2 reduction. Mechanistic studies suggest that n-propanol could be formed through the C-C coupling of carbon monoxide and ethylene precursors. The enhanced activity of the Cu nanocrystals toward n-propanol formation was correlated to their surface population of defect sites.

Copper electrodes have been shown to be selective toward the electroreduction of carbon dioxide to ethylene, carbon monoxide, or formate. However, the underlying causes of their activities, which have been attributed to a rise in local pH near the surface of the electrode, presence of atomic-scale defects, and/or residual oxygen atoms in the catalysts, etc., have not been generally agreed on. Here, we perform a study of carbon dioxide reduction on four copper catalysts from −0.45 to −1.30 V vs. reversible hydrogen electrode. The selectivities exhibited by 20 previously reported copper catalysts are also analyzed. We demonstrate that the selectivity of carbon dioxide reduction is greatly affected by the applied potentials and currents, regardless of the starting condition of copper catalysts. This study shows that optimization of the current densities at the appropriate potential windows is critical for designing highly selective copper catalysts.

Copper oxides have been of considerable interest as electrocatalysts for CO reduction (CO2R) in aqueous electrolytes. However, their role as an active catalyst in reducing the required overpotential and improving the selectivity of reaction compared with that of polycrystalline copper remains controversial. Here, we introduce the use of selected-ion flow tube mass spectrometry, in concert with chronopotentiometry, in situ Raman spectroscopy, and computational modeling, to investigate CO2R on CuO nanoneedles, CuO nanocrystals, and CuO nanoparticles. We show experimentally that the selective formation of gaseous C products (i.e., ethylene) in CO2R is preceded by the reduction of the copper oxide (CuOR) surface to metallic copper. On the basis of density functional theory modeling, CO2R products are not formed as long as CuO is present at the surface because CuOR is kinetically and energetically more favorable than CO2R.