–CH₃ Mediated Pathway for the Electroreduction of CO₂ to Ethane and Ethanol on Thick Oxide-Derived Copper Catalysts at Low Overpotentials

Abstract

Oxide-derived copper is known for its unique ability to catalyze the selective electroreduction of CO2 to C2 and higher carbon compounds at low overpotentials. To understand this phenomenon, mechanistic studies typically chose ethylene (C2H4) as the model compound. The pathways to form other C2 compounds such as ethane (C2H6) and ethanol are then generally considered to be similar to that of C2H4. However, regular detection of C2H6 or ethanol on thick oxide-derived Cu at low overpotentials, often with selectivities exceeding that of C2H4, raises an important question: does the formation of these two C2 molecules really share a common route with C2H4? In this work, through an investigation of CO2 electroreduction on oxide-derived Cu of different thicknesses and oxidation states, we show that the formation of C2H6 and ethanol on thick oxide-derived Cu films could proceed through routes distinct from that of C2H4 at low overpotentials. Investigations using select molecular precursors such as diacetyl [(CH3CO)2] suggest that the formation of C2H6 on thick oxide-derived Cu surfaces is likely to originate from the dimerization of −CH3 intermediates. We attribute the higher selectivity for C2H6 and ethanol to a higher population of Cu+ sites in the thick oxide-derived Cu films, which helped to stabilize the −CH3 intermediates.

Nanostructured Copper‐Based Electrocatalysts for CO2 Reduction

“…[95,96] To provide more evidence of the nanostructure effect on Cu electrode, 2D nanostructures of thin copper layers deposited on other metal substrates were measured. [97][98][99][100][101] The activity and selectivity properties of such thin layers could be altered due to the effects of lattice strain and layer-substrate electron interaction. [102] Reske et al investigated the catalytic behaviors of ECR on copper overlayers with different atomic-scale thickness ranging from monolayer to 15 nm supported on a polycrystalline Pt substrate (Figure 6a).…”

Understanding the Heterogeneous Electrocatalytic Reduction of Carbon Dioxide on Oxide‐Derived Catalysts

“…An alternative C−C coupling process involving the coupling of two *CH 3 groups has been proposed to form products such as C 2 H 6 and ethanol at low overpotential . The higher selectivity for C 2 H 6 and ethanol were attributed to stabilization of the *CH 3 intermediates by a high population of Cu + sites in the thick OD−Cu films employed …”

“…[45,50,51,67,85,86] An alternative CÀC coupling process involving the coupling of two *CH 3 groups has been proposed to form products such as C 2 H 6 and ethanol at low overpotential. [87] The higher selectivity for C 2 H 6 and ethanol were attributed to stabilization 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 of the *CH 3 intermediates by a high population of Cu + sites in the thick ODÀCu films employed. [87] Besides the dimerization of CO or *CH 3 , another proposed mechanism involves a Fischer-Tropsch-like mechanism for the formation of C2-C3 products, particularly alcohols.…”

“…[87] The higher selectivity for C 2 H 6 and ethanol were attributed to stabilization 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 of the *CH 3 intermediates by a high population of Cu + sites in the thick ODÀCu films employed. [87] Besides the dimerization of CO or *CH 3 , another proposed mechanism involves a Fischer-Tropsch-like mechanism for the formation of C2-C3 products, particularly alcohols. [47,51] In this process, free CO is believed to insert in the bond between Cu and adsorbed C1/C2 species such as *CH 2 .…”

Electrochemical Carbon Dioxide Splitting

“…Oxide derived strategy proved to be effective synthesis to obtain C2+ formation on Cu based catalysts . Part of them was ascribed to the Cu(I) as active species,, while another part of them was owing to the metallic Cu active sites with morphology optimization or subsurface oxygen residual ,,. Natural oxidation of Cu in the air as well as in water media makes it harder to identify the true active species and influence factors during catalysis via ex situ and even some in situ characterizations.…”