On-Surface Modification of Copper Cathodes by Copper(I)-Catalyzed Azide Alkyne Cycloaddition and CO2 Reduction in Organic Environments

Abstract

In this study, organic structures were introduced onto copper cathodes to induce changes in their electrocatalytic CO 2 reduction activity. Poorly soluble organic polymers were distributed onto the copper surface as a thin layer by polymerizing monomeric precursors via a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) activated by anodization of the copper substrate. The resulting structure possesses copper surface atoms that are available to participate in the CO 2 reduction reaction-comparable to close-contact organic structures-and stabilize the adsorption of organic layers through the CO 2 reduction process. The CO 2 reduction performance of the on-surface modified copper cathode exhibited improved CO 2 reduction over H 2 evolution compared with traditional cast modification systems. Preventing organic moieties from forming densely packed assemblies on the metal surface appears to be important to promote the CO 2 reduction process on the copper atoms. The suppression of H 2 evolution, a high methane/ethylene ratio, and the influence of stirring demonstrate that the improved CO 2 reduction activity is not only a result of the copper atom reorganization accompanied by repeating anodization for modification; the organic layer also apparently plays an important role in proton transfer and CO 2 accumulation onto the copper surface.

Electrochemical CO2 Reduction on Polycrystalline Copper by Modulating Proton Transfer with Fluoropolymer Composites

“…For these reasons, the fabrication of novel CO 2 reduction electrodes with high durability and selectivity toward carbon-containing products is a grand challenge. Methods for designing these electrodes include tuning the morphology of the catalyst, − surface modification, − alloying multiple metals, − controlling the pH at the electrode–electrolyte interface, − utilizing non-aqueous solvents, − and controlling proton- and electron-transfer rates. − For example, Dinh et al were able to convert CO 2 to ethylene with a high Faradaic efficiency of 70% at −0.55 V versus reversible hydrogen electrode (RHE) using a Cu electrode in alkaline media. They proposed that the hydroxide ions on or near the Cu surface lower the CO 2 reduction and CO–CO coupling activation energy barriers .…”

Efficient strategies for promoting the electrochemical reduction of CO2 to C2+ products over Cu-based catalysts

“…A series of hydrophobic N-containing polymers have also been used to modify the hydrophobicity of Cu catalyst surfaces [85,[93][94][95][96][97]. Polyaniline-coated Cu foil electrodes produced by drop casting exhibited a superior activity toward the CO2RR (rather than the HER), with a significant enhancement in the FE of C2+ products from 15% to 60% at -1.1 V vs. RHE by remarkably decreasing the H2 FE from > 40% to < 15% [85].…”

“…Organic layers coated on the electrode surface can limit the diffusion of trace amounts of metal impurities (i.e., Fe 2+ and Zn 2+ ) from the electrolyte to the electrode surface, which could poison the active sites [82]. In addition, the Cu species can be stabilized against decomposition, elution, and corrosion during the electrochemical reaction by the protective organic layer, resulting in improved catalytic stability [94,96,97,102].…”

“…Nevertheless, elaborate organic layers coated on the electrode surface can limit the diffusion of trace impurities in the electrolyte to the electrode surface, which can poison the active sites [82]. Protective organic layers can ensure high catalytic stability by stabilizing the Cu species against decomposition, elution, and corrosion during the electrochemical reaction [94,96,97,102].…”

Uniform wrapping of copper(i) oxide nanocubes by self-controlled copper-catalyzed azide–alkyne cycloaddition toward selective carbon dioxide electrocatalysis

“…Copper-catalyzed azide-alkyne cycloaddition (CuAAC) is especially suitable for our requirements because it can make a robust linkage between the organic monomers by various copper compounds. 27,28 We previously reported a modification of anodized copper by CuAAC, which resulted in an improved CO 2 reduction selectivity, 29,30 but the prepared surface was composed of a rather random aggregation of organic layers and redeposited copper. These results motivated us to use an ordered Cu(I) solid surface as a platform for modification and CO 2 reduction to bring out the full potential of the contact surface.…”