Electrocatalytic CO2 Reduction on CuOx Nanocubes: Tracking the Evolution of Chemical State,Geometric Structure,and Catalytic Selectivity using Operando Spectroscopy

The direct electrochemical conversion of carbon dioxide (CO₂) into multi-carbon (C₂₊) products still faces fundamental and technological challenges. While facet-controlled and oxide-derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. Herein we uncover changes in the chemical and morphological state of supported and unsupported Cu₂O nanocubes during operation in low-current H-Cells and in high-current gas diffusion electrodes (GDEs) using neutral pH buffer conditions. While unsupported nanocubes achieved a sustained C₂₊ Faradaic efficiency of around 60 % for 40 h, the dispersion on a carbon support sharply shifted the selectivity pattern towards C₁ products. Operando XAS and time-resolved electron microscopy revealed the degradation of the cubic shape and, in the presence of a carbon support, the formation of small Cu-seeds during the surprisingly slow reduction of bulk Cu₂O. The initially (100)-rich facet structure has presumably no controlling role on the catalytic selectivity, whereas the oxide-derived generation of under-coordinated lattice defects, can support the high C₂₊ product yields.     

Facet‐Dependent Catalytic Activity of Cu2O Nanocrystals in the One‐Pot Synthesis of 1,2,3‐Triazoles by Multicomponent Click Reactions

We report the highly facet‐dependent catalytic activity of Cu₂O nanocubes, octahedra, and rhombic dodecahedra for the multicomponent direct synthesis of 1,2,3‐triazoles from the reaction of alkynes, organic halides, and NaN₃. The catalytic activities of clean surfactant‐removed Cu₂O nanocrystals with the same total surface area were compared. Rhombic dodecahedral Cu₂O nanocrystals bounded by {110} facets were much more catalytically active than Cu₂O octahedra exposing {111} facets, whereas Cu₂O nanocubes displayed the slowest catalytic activity. The superior catalytic activity of Cu₂O rhombic dodecahedra is attributed to the fully exposed surface Cu atoms on the {110} facet. A large series of 1,4‐disubstituted 1,2,3‐triazoles have been synthesized in excellent yields with high regioselectivity under green conditions by using these rhombic dodecahedral Cu₂O catalysts, including the synthesis of rufinamide, an antiepileptic drug, demonstrating the potential of these nanocrystals as promising heterogeneous catalysts for other important coupling reactions.     

Dynamic Changes in the Structure,Chemical State and Catalytic Selectivity of Cu Nanocubes during CO2 Electroreduction: Size and Support Effects

In situ and operando spectroscopic and microscopic methods were used to gain insight into the correlation between the structure, chemical state, and reactivity of size‐ and shape‐controlled ligand‐free Cu nanocubes during CO₂ electroreduction (CO₂RR). Dynamic changes in the morphology and composition of Cu cubes supported on carbon were monitored under potential control through electrochemical atomic force microscopy, X‐ray absorption fine‐structure spectroscopy and X‐ray photoelectron spectroscopy. Under reaction conditions, the roughening of the nanocube surface, disappearance of the (100) facets, formation of pores, loss of Cu and reduction of CuO_x species observed were found to lead to a suppression of the selectivity for multi‐carbon products (i.e. C₂H₄ and ethanol) versus CH₄. A comparison with Cu cubes supported on Cu foils revealed an enhanced morphological stability and persistence of Cu^I species under CO₂RR in the former samples. Both factors are held responsible for the higher C₂/C₁ product ratio observed for the Cu cubes/Cu as compared to Cu cubes/C. Our findings highlight the importance of the structure of the active nanocatalyst but also its interaction with the underlying substrate in CO₂RR selectivity.     

Dynamic Changes in the Structure,Chemical State and Catalytic Selectivity of Cu Nanocubes during CO2 Electroreduction: Size and Support Effects

In situ and operando spectroscopic and microscopic methods were used to gain insight into the correlation between the structure, chemical state, and reactivity of size‐ and shape‐controlled ligand‐free Cu nanocubes during CO₂ electroreduction (CO₂RR). Dynamic changes in the morphology and composition of Cu cubes supported on carbon were monitored under potential control through electrochemical atomic force microscopy, X‐ray absorption fine‐structure spectroscopy and X‐ray photoelectron spectroscopy. Under reaction conditions, the roughening of the nanocube surface, disappearance of the (100) facets, formation of pores, loss of Cu and reduction of CuO_x species observed were found to lead to a suppression of the selectivity for multi‐carbon products (i.e. C₂H₄ and ethanol) versus CH₄. A comparison with Cu cubes supported on Cu foils revealed an enhanced morphological stability and persistence of Cu^I species under CO₂RR in the former samples. Both factors are held responsible for the higher C₂/C₁ product ratio observed for the Cu cubes/Cu as compared to Cu cubes/C. Our findings highlight the importance of the structure of the active nanocatalyst but also its interaction with the underlying substrate in CO₂RR selectivity.     

Cu2O-Ag Tandem Catalysts for Selective Electrochemical Reduction of CO2 to C2 Products

The electrochemical carbon dioxide reduction reaction (CO₂RR) to C₂ chemicals has received great attention. Here, we report the cuprous oxide (Cu₂O) nanocubes cooperated with silver (Ag) nanoparticles via the replacement reaction for a synergetic CO₂RR. The Cu₂O-Ag tandem catalyst exhibits an impressive Faradaic efficiency (FE) of 72.85% for C₂ products with a partial current density of 243.32 mA·cm⁻². The electrochemical experiments and density functional theory (DFT) calculations reveal that the introduction of Ag improves the intermediate CO concentration on the catalyst surface and meanwhile reduces the C-C coupling reaction barrier energy, which is favorable for the synthesis of C₂ products.     

Selective CO2 Electroreduction to Ethylene and Multicarbon Alcohols via Electrolyte‐Driven Nanostructuring

Production of multicarbon products (C₂₊) from CO₂ electroreduction reaction (CO₂RR) is highly desirable for storing renewable energy and reducing carbon emission. The electrochemical synthesis of CO₂RR catalysts that are highly selective for C₂₊ products via electrolyte‐driven nanostructuring is presented. Nanostructured Cu catalysts synthesized in the presence of specific anions selectively convert CO₂ into ethylene and multicarbon alcohols in aqueous 0.1 m KHCO₃ solution, with the iodine‐modified catalyst displaying the highest Faradaic efficiency of 80 % and a partial geometric current density of ca. 31.2 mA cm^?2 for C₂₊ products at ?0.9 V vs. RHE. Operando X‐ray absorption spectroscopy and quasi in situ X‐ray photoelectron spectroscopy measurements revealed that the high C₂₊ selectivity of these nanostructured Cu catalysts can be attributed to the highly roughened surface morphology induced by the synthesis, presence of subsurface oxygen and Cu⁺ species, and the adsorbed halides.     

Morphology‐Directed Selective Production of Ethylene or Ethane from CO2 on a Cu Mesopore Electrode

The electrocatalytic conversion of CO₂ to value‐added hydrocarbons is receiving significant attention as a promising way to close the broken carbon‐cycle. While most metal catalysts produce C₁ species, such as carbon monoxide and formate, the production of various hydrocarbons and alcohols comprising more than two carbons has been achieved using copper (Cu)‐based catalysts only. Methods for producing specific C₂ reduction outcomes with high selectivity, however, are not available thus far. Herein, the morphological effect of a Cu mesopore electrode on the selective production of C₂ products, ethylene or ethane, is presented. Cu mesopore electrodes with precisely controlled pore widths and depths were prepared by using a thermal deposition process on anodized aluminum oxide. With this simple synthesis method, we demonstrated that C₂ chemical selectivity can be tuned by systematically altering the morphology. Supported by computational simulations, we proved that nanomorphology can change the local pH and, additionally, retention time of key intermediates by confining the chemicals inside the pores.     

Stability of Residual Oxides in Oxide‐Derived Copper Catalysts for Electrochemical CO2 Reduction Investigated with 18O Labeling

Oxide‐derived (OD) Cu catalysts have high selectivity towards the formation of multi‐carbon products (C₂/C₃) for aqueous electrochemical CO₂ reduction (CO₂R). It has been proposed that a large fraction of the initial oxide can be surprisingly resistant to reduction, and these residual oxides play a crucial catalytic role. The stability of residual oxides was investigated by synthesizing ¹⁸O‐enriched OD Cu catalysts and testing them for CO₂R. These catalysts maintain a high selectivity towards C₂/C₃ products (ca. 60 %) for up to 5 h in 0.1 m KHCO₃ at ?1.0 V vs. RHE. However, secondary‐ion mass spectrometry measurements show that only a small fraction (<1 %) of the original ¹⁸O content remains, showing that residual oxides are not present in significant amounts during CO₂R. Furthermore, we show that OD Cu can reoxidize rapidly, which could compromise the accuracy of ex situ methods for determining the true oxygen content.     

A tetranuclear copper(II) cluster: bis(μ‐4‐chlorobenzoato‐κ2O:O′)(4‐chlorobenzoato‐κ2O,O′)(4‐chlorobenzoato‐κO)tetrakis(μ3‐2‐pyridylmethanolato‐κ4N,O:O:O)tetracopper(II)

The title compound, [Cu₄(C₇H₄ClO₂)₄(C₆H₆NO)₄], consists of isolated tetranuclear clusters, where the Cu²⁺ cations are five‐ and sixfold coordinated by O atoms from the 4‐chlorobenzoate anions and by pyridine N and methanolate O atoms from bidentate 2‐pyridylmethanolate ligands. While three Cu atoms are six‐coordinated by an NO₅ donor set forming distorted octahedra, the fourth Cu atom is five‐coordinated by an NO₄ donor set forming a distorted tetragonal–pyramidal coordination around the Cu atom. The nucleus is a deformed cubane‐like Cu₄O₄ structure, with Cu...Cu distances in the range 3.0266 (11)–3.5144 (13) Å.     

Crystal‐Plane‐Controlled Selectivity of Cu2O Catalysts in Propylene Oxidation with Molecular Oxygen

The selective oxidation of propylene with O₂ to propylene oxide and acrolein is of great interest and importance. We report the crystal‐plane‐controlled selectivity of uniform capping‐ligand‐free Cu₂O octahedra, cubes, and rhombic dodecahedra in catalyzing propylene oxidation with O₂: Cu₂O octahedra exposing {111} crystal planes are most selective for acrolein; Cu₂O cubes exposing {100} crystal planes are most selective for CO₂; Cu₂O rhombic dodecahedra exposing {110} crystal planes are most selective for propylene oxide. One‐coordinated Cu on Cu₂O(111), three‐coordinated O on Cu₂O(110), and two‐coordinated O on Cu₂O(100) were identified as the catalytically active sites for the production of acrolein, propylene oxide, and CO₂, respectively. These results reveal that crystal‐plane engineering of oxide catalysts could be a useful strategy for developing selective catalysts and for gaining fundamental understanding of complex heterogeneous catalytic reactions at the molecular level.     

Highly Facet‐Dependent Photocatalytic Properties of Cu2O Crystals Established through the Formation of Au‐Decorated Cu2O Heterostructures

This work confirms the presence of a large facet‐dependent photocatalytic activity of Cu₂O crystals through sparse deposition of gold particles on Cu₂O cubes, octahedra, and rhombic dodecahedra. Au‐decorated Cu₂O rhombic dodecahedra and octahedra showed greatly enhanced photodegradation rates of methyl orange resulting from a better separation of the photogenerated electrons and holes, with the rhombic dodecahedra giving the best efficiency. Au–Cu₂O core–shell rhombic dodecahedra also displayed a better photocatalytic activity than pristine rhombic dodecahedra. However, Au‐deposited Cu₂O cubes, pristine cubes, and Au‐deposited small nanocubes bound by entirely {100} facets are all photocatalytically inactive. X‐ray photoelectron spectra (XPS) showed identical copper peak positions for these Au‐decorated crystals. Remarkably, electron paramagnetic resonance (EPR) measurements indicated a higher production of hydroxyl radicals for the photoirradiated Cu₂O rhombic dodecahedra than for the octahedra, but no radicals were produced from photoirradiated Cu₂O cubes. The Cu₂O {100} face may present a high energy barrier through its large band edge bending and/or electrostatic repulsion, preventing charge carriers from reaching to this surface. The conventional photocatalysis model fails in this case. The facet‐dependent photocatalytic differences should be observable in other semiconductor systems whenever a photoinduced charge‐transfer process occurs across an interface.     

Facile Synthesis of Cuprous Oxide/Gold Nanocomposites for Nonenzymatic Amperometric Sensing of Hydrogen Peroxide

In this work, a facile preparation method of cuprous oxide/gold (Cu₂O/Au) nanocomposite was successfully developed. The process consisted of one‐pot co‐reduction of HAuCl₄ and CuSO₄ using ascorbic acid (AA) as a reducing agent at room temperature under magnetic stirring. The structures and compositions of the as‐prepared products were characterized by SEM, EDS, and XRD. Cyclic voltammetry and chronopotentiometry studies revealed that the as‐prepared cubic Cu₂O/Au nanocomposites showed enhanced performance towards the non‐enzymatic catalytic reduction of hydrogen peroxide (H₂O₂) when compared to single‐component Cu₂O nanocubes. The linear range of H₂O₂ determination spanned over 4 orders of magnitude (1 μM∼16.7 mM) and the detection limit was low as 0.45 μM (S/N=3). The enhanced performance of cubic Cu₂O/Au was attributed to: i) the synergistic effect between Cu₂O and Au, ii) the increase in surface area induced by the reduced size of the nanocubes, and iii) the improved electrical conductivity due to the presence of Au in the particles. Overall, the cubic Cu₂O/Au nanocomposites prepared by the proposed method hold great promise for future practical use in H₂O₂ detection.     

A Facile Chemical Synthesis of Cu2O Nanocubes Covered with Co3O4 Nanohexagons for the Sensitive Detection of Glucose

Copper (I) oxide nanocubes (Cu₂O NCs) covered with cobalt oxide nanohexagons (Co₃O₄ NHs) were prepared through simple chemical method. Here, ascorbic acid is used as reducing and capping agent for the synthesis of nanocubes and nanohexagons. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy‐dispersive X‐ray spectroscopy (EDX) and X‐ray diffraction spectroscopy (XRD) were employed to confirm the prepared nanocomposite. Cu₂O NCs?Co₃O₄ NHs nanocomposite is drop cast on the glassy carbon electrode (GCE) for the fabrication of glucose sensor. The fabricated Cu₂O NCs?Co₃O₄ NHs/GCE exhibited a better electrocatalytic activity towards the determination of glucose than that of individually fabricated Cu₂O NCs and Co₃O₄ NHs modified GCE. Our finding exhibited a wide linear range from 1 μM to 5330 μM with LOD of 0.63 towards glucose. In addition, the sensor attained appreciable stability, repeatability and reproducibility. Practicality of the sensor was demonstrated in human serum samples. The main advantages of the fabricated sensor are simple, biocompatible, cost effective, fast response and highly stable electrode surface.     

Manipulating the Oxidation State of CuxO Catalysts to Optimize the Selectivity of Gaseous Products in Electrochemical CO2 Reduction

Copper-based (Cu-based) catalysts can efficiently convert carbon dioxide to multicarbon products by electrochemical reduction. In this paper, the electrocatalyst with the coexistence of three valence states of Cu(0)-Cu(I)-Cu(II) was successfully prepared by adjusting the experimental conditions. The catalyst was derived from Cu/Cu₂O prepared on carbon cloth and exhibited excellent CO₂ reduction performance. For carbon-gaseous products, the Faradaic efficiencies for the Cu-2 catalyst consisting of Cu(0)-Cu(I)-Cu(II) were 35.45±3.40 % at −1.66 V vs. RHE, of which 23.85±1.18 % for C₂H₄. And the synergistic effect of Cu(0)-Cu(I)-Cu(II) significantly improved the selectivity of the catalyst to C₂H₄. This paper provided an efficient method to rationally tune the valence state of Cu-based catalysts to improve CO₂ reduction performance.     

Surfactant-free fabrication of Cu2O nanosheets from Cu colloids and their tunable optical properties

Novel sheetlike Cu₂O two-dimensional (2D) nanoarchitectures were successfully synthesized via a copper nanoparticle-mediated process for the first time. Uniform and nearly monodisperse Cu nanocolloids were firstly synthesized by disproportionating reaction of Cu⁺ at the surfactant-free ambient conditions, and Cu₂O nanosheets were subsequently synthesized by choosing ethanol solvent agent to limit the oxidized processes of Cu nanocolloids. The synthesized products were systematically studied by X-ray powder diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis absorption spectra. It was demonstrated that the solvent agent of ethanol played key roles in the formation of the as-synthesized nanosheets. By choosing the different solvent agents to limit the oxidized processes, Cu₂O nanospheres and nanocubes can be selectively synthesized accordingly.     

Bis(μ‐di‐2‐pyridyl­aminato 1‐oxide)­bis­[(tri­fluoro­acetato)copper(II)] aceto­nitrile disolvate

The crystal structure of the title compound, [Cu₂(C₂F₃O₂)₂(C₁₀H₈N₃O)₂]·2CH₃CN, contains discrete [Cu₂(CF₃COO)₂(O‐dpa)₂] mol­ecules (O‐dpaH is di‐2‐pyridyl­amine 1‐oxide) which have imposed crystallographic twofold symmetry and an aceto­nitrile mol­ecule of solvation. The O‐dpa⁻ ligand is both bidentate and bridging, linking two Cu atoms with a separation of 3.4270 (11) Å. Each Cu atom is surrounded by four coordinated atoms that are almost coplanar, with dimensions Cu—N = 1.940 (2) and 1.984 (3) Å, and Cu—O = 1.912 (2) and 1.945 (2) Å.     

The composite catalysts of Cu/CuxO nanoparticles supported on the carbon fibers were prepared for styrene oxidation reaction

In this paper a novel simple method for preparing two different catalysts with various‐valences copper was reported. Carbon nanofibers supported copper‐cuprous oxide nanoparticles (Cu‐Cu₂O NPs/CNFs) and copper oxide nanoparticles (CuO NPs/CNFs) through electrospinning, adsorption and reduction in the high‐pressure hydrogenation and the high‐temperature calcination methods. These catalysts were investigated by a series of characterizations and were applied in reaction in nitrogen atmosphere, which had a good catalytic activity and selectivity of benzaldehyde for the reaction. Above all, the new study has been certified clearly, in which Cu‐Cu₂O NPs/CNFs and CuO NPs/CNFs composite catalysts enhanced the generation of benzaldehydeand the excellent catalytic properties were exhibited.     

Electrocatalytic Oxidation of Dopamine at a Nanocuprous Oxide‐Methylene Blue Composite Glassy Carbon Electrode

Cuprous oxide nanowhisker was prepared by using cetyltrimethyl ammonium bromide (CATB) as soft template, and was characterized by XRD and TEM methods. The electrochemical properties of nano‐Cu₂O and nano‐Cu₂O‐methylene blue (MB) modified electrode were studied. The experimental results indicate that nano‐Cu₂O shows a couple of redox peaks corresponding to the redox of Cu(II)/Cu(I), the peak currents are linear to the scan rates which demonstrate that the electrochemical response of Cu₂O is surface‐controlled. The composite nano‐Cu₂O‐Nafion‐MB modified electrode shows a trend of decrease of peak currents corresponding to the Cu (II)/Cu (I). However, the electrocatalytic ability of nano‐Cu₂O‐MB composite film to dopamine increases dramatically. At this composite electrode, dopamine shows a couple of quasireversible redox peaks with a peak separation of 106 mV, the peak current increases about 8 times and the oxidation peak potential decreases about 200 mV as compared to that at bare glassy carbon electrode. The peak currents change linearly with concentration of dopamine from 1×10^?7 to 3.2×10^?4 mol/L, the detection limit is 4.6×10^?8 mol/L. The composite electrode can effectively eliminate the interference of ascorbic acid and has better stability and excellent reproducibility.     

Morphology-Directed Selective Production of Ethylene or Ethane from CO2 on a Cu Mesopore Electrode

The electrocatalytic conversion of CO₂ to value-added hydrocarbons is receiving significant attention as a promising way to close the broken carbon-cycle. While most metal catalysts produce C₁ species, such as carbon monoxide and formate, the production of various hydrocarbons and alcohols comprising more than two carbons has been achieved using copper (Cu)-based catalysts only. Methods for producing specific C₂ reduction outcomes with high selectivity, however, are not available thus far. Herein, the morphological effect of a Cu mesopore electrode on the selective production of C₂ products, ethylene or ethane, is presented. Cu mesopore electrodes with precisely controlled pore widths and depths were prepared by using a thermal deposition process on anodized aluminum oxide. With this simple synthesis method, we demonstrated that C₂ chemical selectivity can be tuned by systematically altering the morphology. Supported by computational simulations, we proved that nanomorphology can change the local pH and, additionally, retention time of key intermediates by confining the chemicals inside the pores.     

Cu/Cu2O Electrodes and CO2 Reduction to Formic Acid: Effects of Organic Additives on Surface Morphology and Activity

Copper/copper oxide (Cu/Cu₂O) electrodes are known to display interesting electrocatalytic performances for the reduction of CO₂, and thus, deserve further investigation for optimization. Here, we show that the addition of nitrogen‐based organic additives greatly improves the activity of these electrodes (higher current densities, greater selectivity, and higher faradaic yields). The best effector is found to be tetramethyl cyclam. For example, electrolysis at ?2.0 V versus Fc⁺/Fc in CO₂‐saturated DMF/H₂O (99:1, v/v) in the presence of this effector results in formic acid with almost 90 % faradaic yield. SEM and XPS analysis of the electrode surface reveals that the organic additive promotes the formation of active Cu⁰ nanoparticles from Cu₂O during electrolysis. This simple approach provides a straightforward strategy toward the optimization of Cu/Cu₂O electrodes.