Fig. 1

Overview of the possible pathways for electrochemical reduction of CO2 to C1 and C2 products. The major products are written in blue, and minor products are in red. Steps denoted as “slow” are potentially rate-determining for a specific pathway and can be used to control the reaction path. The two CO2- species are marked by an asterisk to indicate which part of the molecule is adsorbed to the electrode surface.

Fig. 2

IR spectra obtained at various applied potentials during a CV carried out in 1 atm CO2-saturated 0.1 mol·L-1 NaHCO3. Reproduced from Ref.[24] with permission from the American Chemical Society. (Direct link: https://pubs.acs.org/doi/10.1021/acscentsci.6b00155. Further permissions related to the material excerpted should be directed to the ACS)

Fig. 3

Faradaic current and mass signals for species generated during a single cyclic voltammogram carried out in 0.05 mol·L-1 (A) glycolaldehyde (blue), glyoxal (green) and (B) ethylene oxide in a phosphate buffer solution (pH = 7) at a scan rate of 1 mV·s-1. Reproduced from Ref.[28] with permission from the Royal Society of Chemistry.

Fig. 4

Faradaic currents and mass signals for m/z = 15 (blue) and m/z = 29, 30, 31 (green) generated during a single cyclic voltammogram carried out in 0.05 mol·L-1 formaldehyde in a phosphate buffer solution (pH = 7) at a scan rate of 1 mV·s-1. Reproduced from Ref.[28] with permission from The Royal Society of Chemistry

Fig. 5

Schematic overview of CO2 reduction to C1 and C2 products as depicted in 2011[28]. Note that the pathway contains many branches not shown, and the actual path of the reaction depends strongly on reaction conditions, as discussed in the text.

Fig. 6

Depiction of the strongly-hydrated Na+ separated from the C2O2 intermediate of the C2 pathway (gray and green circles represent carbon and oxygen, respectively, on the copper surface) by hydration layer, and weakly-hydrated Cs+ in close proximity to the C2O2 intermediate. The y-axis depicts the qualitative effect on the energy of the reaction intermediate.

Fig. 7

(A) Copper atoms arranged to form a (100) surface, with CO molecules (gray and green concentric circles represent carbon and oxygen, respectively) bound to bridge sites to form C2O2. (B) Copper atoms arranged to form a (111) surface with CO molecules bound at bridge sites too close to easily form C2O2.