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 i...

Selective Electrochemical Reduction of Carbon Dioxide to Ethylene and Ethanol on Copper(I) Oxide Catalysts

On the basis of constraints from reported experimental observations and density functional theory simulations, we propose a mechanism for the reduction of CO2 to C2 products on copper electrodes. To model the effects of an applied potential bias on the reactions, calculations are carried out with a variable, fractional number of electrons on the unit cell, which is optimized so that the Fermi level matches the actual chemical potential of electrons (i.e., the applied bias); an implicit electrolyte model allows for compensation of the surface charge so that neutrality is maintained in the overall simulation cell. Our mechanism explains the presence of the seven C2 species that have been detected in the reaction, as well as other notable experimental observations. Furthermore, our results shed light on the difference in activities toward C2 products between the (100) and (111) facets of copper. We compare our methodologies and findings with those in other recent mechanistic studies of the copper-catalyzed C...

/pdf/mechanism-of-co2-reduction-at-copper-surfaces-pathways-to-c2-34c1bj784l.pdf

Mechanism of CO2 Reduction at Copper Surfaces: Pathways to C2 Products

Developing hierarchical electrocatalysts for the oxygen evolution reaction (OER) is of great importance for electrochemical hydrogen production. Here, we describe the development of a hierarchical CuO@NiCo layered double hydroxide core–shell nanoarray on copper foil (CuO@NiCo LDH/CF) as a 3D OER electrocatalyst. When tested in 1.0 M KOH, such CuO@NiCo LDH/CF offers superior catalytic activity with a geometrical catalytic current density of 20 mA cm−2 at an overpotential of only 256 mV. It also shows strong long-term electrochemical durability to retain its activity for at least 24 h.

A hierarchical CuO@NiCo layered double hydroxide core–shell nanoarray as an efficient electrocatalyst for the oxygen evolution reaction

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.

/pdf/the-effects-of-currents-and-potentials-on-the-selectivities-42m8qfxlyq.pdf

The effects of currents and potentials on the selectivities of copper toward carbon dioxide electroreduction

Cuprous oxide (Cu(2)O) and cupric oxide (CuO) nanowires have started playing important roles in energy conversion devices and optoelectronic devices. Although the desired advanced properties have been demonstrated, these materials cannot yet be produced in large-bulk quantities in order to bridge the technological transfer gap for wider use. In this respect, the quest for the most efficient synthesis process which yields not only large quantities but also high quality and advanced material properties continues. This paper gives an extensive review of copper oxide nanowire (NW) synthesis by all methods and routes by which various researchers have obtained their nanomaterial. These methods are critically overviewed, evaluated and compared. Methods of copper oxide NW growth include wet-chemical methods based on pure solution growth, electrochemical and hydrothermal routes as well as thermal and plasma oxidation methods. In terms of advanced nanowire synthesis, the fast thermal method or direct plasma oxidation as well as the combined hybrid wet-chemical method in which copper hydroxide NWs are produced and sequentially transformed by plasma oxidation which produces Cu(2)O NWs are seen as the most promising methods to explore in the near future. These methods not only yield large quantities of NWs, but produce high quality material with advanced properties.

https://iopscience.iop.org/article/10.1088/0957-4484/23/19/194001/pdf

Copper oxide nanowires: a review of growth.

The Pourbaix diagrams (potential-pH diagrams) for copper at 25 to 300°C have been revised. Extrapolation of thermochemical data to elevated temperatures has been performed with the revised model of Helgeson-Kirkham-Flowers, which also allows uncharged aqueous complexes, such as CuOH(aq) and Cu(OH) 2 (aq), to be handled. Calculated high temperature thermodynamic data have been fitted against experimental data at elevated temperature. The hydrolysis of copper(I) and (II) is included with two and four hydroxide complexes, respectively. The Pourbaix diagrams show that the oxides (Cu 2 O(cr) and CuO(cr)) are stable at 25 to 200°C at 10 -6 mol kg -1 of dissoived species, and at 300°C only CuO is stable. The oxides are stable at 25°C at 10 -6 mol kg -1 , but at 100 to 300°C no solid compound is stable.

https://iopscience.iop.org/article/10.1149/1.1838036/pdf

Revised Pourbaix Diagrams for Copper at 25 to 300°C

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Revised Pourbaix Diagrams for Copper at 25 to 300°C