Selective CO₂ Reduction to Ethylene Using Imidazolium-Functionalized Copper

Abstract

Electrochemical CO2 reduction is a promising approach to obtain sustainable chemicals in energy conversion. Improving the selectivity of CO2 reduction toward a particular C2 product such as ethylene remains a significant challenge. Herein, we report a series of imidazolium hexafluorophosphate compounds as surface modifiers for planar Cu foils to boost the Faradaic efficiency (FE) of ethylene from 5 to 73%, which is among the highest reported using polycrystalline Cu. The modified electrodes are convenient to prepare. The structure–function study demonstrates that varying the alkyl or aromatic substituents on the imidazolium nitrogen atoms has significant effects on the morphology of the deposited films and the product selectivity of CO2 reduction. Experimental FEC≥2, FEC2H4, ln­(FEC≥2/FECH4 ), and ln­(FEC2H4 /FEC2H5OH) values show generally linear relationships with FEH2 while using different imidazolium modifiers, suggesting that factors governing proton reduction may also be directly related to both overall C≥2 generation and ethylene selectivity. This work presents an effective and practical way in tailoring the active sites of metallic surface for selective CO2 reduction.

Ionomers Modify the Selectivity of Cu‐Catalyzed Electrochemical CO2 Reduction

“…A lower amount of CO is produced compared to C 2+ products at −100 mA cm −2 and −200 mA cm −2 . These results are consistent with previous reports of CO 2 reduction on Cu [21,25–28] …”

“…These results are consistent with previous reports of CO 2 reduction on Cu. [21,[25][26][27][28] At À 20 mA cm À 2 , the addition of Nafion decreased HER while slightly changed the FEs of other product such as formate and C 2 H 4 . The result at À 20 mA cm À 2 is largely in line with the study of Bell and co-workers, [20] who studied the influence of a thin layer (e. g., 30 nm) of Nafion on Cu at low current densities (j J j < 25 mA cm À 2 ).…”

Copper phenanthroline for selective electrochemical CO2reduction on carbon paper

“…Although the exact nature of the organic ligand in tuning the selectivity of ethylene and ethanol is unclear, previous studies have proposed that local hydrophobicity changed by the imidazolium organic modifier may greatly influence the ethylene selectivity. 15 We have also reported a linear correlation between ln(FE C 2 H 4 /FE C 2 H 5 OH ) and FE H2 using imidazolium functionalized Cu catalysts. 15 b Thus, the normal phenanthroline ligands, that coordinate to the heterogeneous Cu, may favor the generation of a *CCH species by deoxygenation of a commonly accepted *HCCOH intermediate in the C 2 pathway.…”

“…15 b Thus, the normal phenanthroline ligands, that coordinate to the heterogeneous Cu, may favor the generation of a *CCH species by deoxygenation of a commonly accepted *HCCOH intermediate in the C 2 pathway. 12 b ,15 Conversely, the pyridinium-functionalized phenanthroline could enhance CO adsorption and the formation of a *HCCHOH intermediate, which eventually leads to the promotion of the FE C 2 H 5 OH . 16…”

Tuning Selectivity of Acidic Carbon Dioxide Electrolysis via Surface Modification

“…Cu-based electrodes functionalized with ILs have been studied much more recently. So far it was limited to H-cells using CO 2 -saturated KHCO 3 solutions, thus providing low current densities (<30 mA·cm –2 ), , and flow cells for alkaline electrolysis using poly-ionic liquids (PILs). , In all of these cases, ILs promoted C 2+ product formation, and ethylene more specifically. In the present study, we report the first results evaluating a Cu-IL electrode for CO 2 RR under highly acidic conditions (pH ≤ 1), at industrially relevant current densities, not only in the presence but also in the absence of alkali metal cations in the electrolyte.…”