Electrochemical and Surface Studies of Carbon Dioxide Reduction to Methane and Ethylene at Copper Electrodes in Aqueous Solutions

Abstract

The electrochemical reduction of CO2 to CH4 and C2H4 in aqueous alkaline solutions at Cu electrodes was studied under potentiostatic conditions at-2.00V vs. SCE. The current at the Cu electrodes and the rate of hydrocarbon formation were monitored as a function of time over a temperature range from 0 to 48~ Solutions of formate, formaldehyde, and methanol, possible intermediates in the reduction process, were also electrolyzed. Surface analyses (XPS and AES) were also performed on the Cu electrodes following electrolysis to identify surface intermediates. In addition to hydrocarbon formation, a poisoning process occurred, causing a deposit of a black film on the surface of the Cu cathode. XPS and AES studies indicated that the black film was graphitic carbon, probably the result of a side reaction, the reduction of CQ through formate to graphite. A tentative reaction mechanism for CO2 reduction, based upon the data here and those of previous investigators, involving the reaction path CO2-* CO ~ surface-bound formyl (Cu-HCO) ~ surface-bound methylene (Cu-CH2)-~ hydrocarbon products, is proposed.

RETRACTED ARTICLE: An overview of CO2 electroreduction into hydrocarbons and liquid fuels on nanostructured copper catalysts

“…Although the conversion mechanism of CO 2 to liquid fuels is not very clear at present but it is widely accepted that CO 2 is first reduced to CO and then it is further converted to alcohols and other hydrocarbons through multistep electron transfer pathways. Earlier studies have found that CO reduction on Cu results in similar products as obtained from CO 2 reduction, proposing that CO was an intermediate in the reduction of CO 2 (44)(45)(46).…”

Polymer-supported CuPd nanoalloy as a synergistic catalyst for electrocatalytic reduction of carbon dioxide to methane

“…Metal impurities in the electrolyte have been removed by preelectrolysis (20), but the formation of graphitic hydrocarbons continues with hydrogen evolution increasing at the expense of CO 2 reduction within an hour after initiation of electrolysis. The change in products is mainly due to the formation of a graphitic carbon layer which prevents CO 2 reduction (39,40). In contrast, nanostructured Cu catalysts have been found to be stable over 5 h of CO 2 electrolysis, with the increase attributed to the higher surface areas at the nanoparticle catalysts (19,41).…”

Electrochemical interfacial influences on deoxygenation and hydrogenation reactions in CO reduction on a Cu(100) surface

“…One important experimental phenomenon is consistent with our results that copper electrode was found to be easily poisoned by graphitic or amorphous carbon formed during electrolysis. [10][11][12] Modulation of electrode potential could effectively avoid the poisoning carbon formation, 51,52 indicating that the carbon species formation resulting from deoxygenation can be controlled by shifting the potential. It is worth mentioning that the electrode potential is kept constant during the coupled proton and electron transfer in reality.…”

“…[1][2][3][4][5] Copper electrode was experimentally found to be able to reduce CO 2 into hydrocarbons (methane and ethylene) uniquely, [6][7][8][9] and the reaction mechanisms were extensively investigated. [10][11][12][13][14][15] It was found that CO was not only the first reduced product but also a new starting species that could be further reduced to the final products of hydrocarbons. The rate-determining step was suggested to be the electron transfer to the adsorbed CO, and the adsorbed COH was proposed to be the crucial intermediate.…”

“…The rate-determining step was suggested to be the electron transfer to the adsorbed CO, and the adsorbed COH was proposed to be the crucial intermediate. [10][11][12][13][14][15] To advance our understanding of the experimental findings, density functional theory (DFT) calculations were employed widely for investigating the mechanisms in CO 2 reduction at the atomic level. [16][17][18][19][20][21][22][23][24][25] Norskov's group has developed a computational hydrogen electrode model to map out the free energy diagrams from CO 2 to CH 4 including about 40 elementary steps on Cu(111).…”