| Citation: |
Jiexin Wen, Lanze Li, Shengbo Zhang, Molly Meng-Jung Li, Jun Yin, Qiong Lei. C–C coupling mechanisms in electrochemical CO2 reduction: pathways to enhanced ethanol selectivity[J]. Energy Lab. doi: 10.54227/elab.20250008
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C–C coupling mechanisms in electrochemical CO2 reduction: pathways to enhanced ethanol selectivity
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Abstract
The electrocatalytic reduction of carbon dioxide (CO2RR) to ethanol represents a promising route for sustainable carbon recycling, yet achieving high selectivity remains a critical challenge due to the complex C–C coupling mechanisms and competing side reactions. This review systematically summarizes recent advances in CO2-to-ethanol conversion using copper-based catalysts, with particular emphasis on the mechanistic pathways of C–C bond formation. Key C–C coupling routes are discussed, including *CO dimerization, *CO–*COH, *CO–*CHO, and *CO–*CHx (x = 1, or 2) coupling, along with their synergistic effects on ethanol selectivity. We also highlight recent progress in
in situ /operando characterization techniques, providing a toolbox for tracking intermediate species and revealing corresponding C–C coupling pathways. Finally, four strategic approaches for enhancing ethanol selectivity are presented, focusing on the rational design of catalyst structure, composition, and interfacial environment. We conclude by outlining current challenges and future directions in the mechanism study on electrocatalytic CO2-to-ethanol conversion, paving the way for the development of next-generation electrocatalytic systems. -
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References
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Jiexin Wen, Lanze Li, Shengbo Zhang, Molly Meng-Jung Li, Jun Yin, Qiong Lei. C–C coupling mechanisms in electrochemical CO2 reduction: pathways to enhanced ethanol selectivity[J]. Energy Lab. doi: 10.54227/elab.20250008
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Figure 1.
Schematic diagram of different C–C coupling pathways in the process of electrocatalytic CO2-to-ethanol conversion.
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Figure 2.
a Electron density difference plots for N-C/Cu with two adsorbed *CO and one charged water layer. Yellow contours represent charge accumulations, and blue contours denote charge depressions.[28] Copyright 2020, Springer Nature. b Scheme of surface F and K co-modified Cu(111) with adsorbed *CO intermediates, c product distributions during CO2RR at various jtotal using the K–F–Cu–CO2 catalyst, free energy diagrams of d *CO–CO coupling on the Cu and K–F–Cu models, and e hydrogenating C2H3O* intermediate to form ethylene and ethanol on K–F–Cu.[25] Copyright 2022, John Wiley and Sons. f TEM image of p-CuO (12.5 nm), the nanocavity structure is highlighted by dashed circles, and the inset illustrates size distributions of these nanocavities, g FEethanol, and h a proposed reaction mechanism for the enhanced CO2RR selectivity to ethanol.[29] Copyright 2023, National Academy of Sciences. i The free energy diagram of CO2RR showing the pathways alongside the key intermediates toward ethanol and C2H4 products on OHad−Cu2O/Cu.[30] Copyright 2024, John Wiley and Sons.
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Figure 3.
a Schematic illustration of *CO–*COH and *CO–*CHO coupling on M@Cu(100) alloy surfaces, M = Pt, Pd, or Au.[31] Copyright 2021, Royal Society of Chemistry. b Free energy diagram of *CO–*CO and *CO–*COH coupling on the fragmented Cu catalyst surface.[32] Copyright 2022, American Chemical Society. c Schematic illustration for the reaction mechanism of CO2-to-ethanol conversion, d free energy diagram for *CO–*COH coupling toward ethanol formation, and e product distributions during CO2RR at different applied potentials over V-doped Cu2Se catalyst.[33] Copyright 2022, John Wiley and Sons.
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Figure 4.
Free energy diagrams of a *CO–*CO and b *CO–*CHO coupling at different potentials.[35] Copyright 2016, American Chemical Society. c HRTEM image of CuOx@C catalyst.[36] Copyright 2022, John Wiley and Sons. d Product distributions during CO2RR at different applied potentials, and e schematic illustration for the reaction mechanism of CO2-to-ethanol conversion on K-doped Cu2Se nanosheet array catalyst.[37] Copyright 2022, John Wiley and Sons. f Free energy diagrams of CO2RR to ethanol in different paths, and g the corresponding optimized intermediate structures involved in ethanol Path 1.[38] Copyright 2024, American Chemical Society.
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Figure 5.
Free energy diagram of a the *CH–*CO coupling to form *CHCO and b the subsequent reduction to form ethanol on Cu(111) surface.[40] Copyright 2020, American Chemical Society. c Schematic illustration of the asymmetric *CH2–*CO coupling process during CO2-to-ethanol conversion, and d product distributions during CO2RR at different applied potentials over layered Cu/Ag tandem catalysts.[41] Copyright 2024, American Chemical Society.
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Figure 6.
a Schematic illustration of CH2=CHO* adsorption on Cu surface toward ethanol formation, and b energy diagram of hydrogenation of C2H3O* to ethylene and ethanol.[48] Copyright 2024, American Chemical Society. c Schematic illustration of CO2-to-ethanol conversion on CuxZn catalyst.[47] Copyright 2016, American Chemical Society.
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Figure 7.
a Schematic illustration of the in situ/operando Raman spectroscopy characterization platform.[53] Copyright 2022, Springer Nature. In situ Raman spectra of b the 34% N-C/Cu catalyst,[28] and c Cu/Ag tandem catalysts (left panel) and the corresponding magnified views for the
2600 ~3000 cm–1 (middle panel) and1300 ~1700 cm–1 (right panel) regions during CO2RR at different applied potentials.[41] Copyright 2020 Springer Nature. Copyright 2024, American Chemical Society. -
Figure 8.
a Schematic illustration of in situ/operando ATR-SEIRAS characterization platform.[30] Copyright 2024, John Wiley and Sons. In situ ATR-SEIRAS spectra of b HA−Cu−OD and c Cu−OD,[30] d fragmented Cu and control Cu[32] during CO2RR at different applied potentials. Copyright 2024, John Wiley and Sons. Copyright 2022, American Chemical Society.
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Figure 9.
a Schematic illustration of the in situ/operando DRIFTS characterization platform.[62] Copyright 2023, Elsevier. Time-resolved in situ DRIFTS spectra comparison between b pristine Cu2Se (left panel) and K11.2%-Cu2Se (right panel) during CO2RR at −0.8 V vs. RHE,[37] c pristine Cu2Se (left panel) and Cu1.22V0.19Se (right panel) during CO2RR.[33] Copyright 2022, John Wiley & Sons. Copyright 2022, John Wiley & Sons.
