(327j) Electrochemically Catalyzed Carbon Dioxide Reduction Reactions and Formation Pathways to Two-Carbon and Three-Carbon Molecules on the Metallic Copper Surfaces

In the present study, we explored the formation mechanisms of two-carbon (C₂, ethylene and ethanol, etc.) and three-carbon (C₃) (propanol and propionaldehyde, etc.) molecules that are produced from the carbon dioxide reduction reaction (CO₂RR) catalyzed by the metallic copper surfaces in the presence of the solvent, electrolyte, and applied electric potential. A complex chemical reaction network that leads to the formation of all possible C₂ and C₃ intermediates and products was established using a combination of density functional theory, basic statistical mechanics, and the classical linearized Poisson−Boltzmann model [J. D. Goodpaster, A. T. Bell, and M. Head-Gordon, J. Phys. Chem. Lett. 2016, 7, 1471]. During this process, we confirmed that the C₂ molecules can be formed via the carbon−carbon (C−C) coupling reaction between surface carbon monoxide (CO) species or their pronated counterparts (CHO) produced from CO₂, prior to the branching point between the ethanol and ethylene pathways, as identified in the previous computational study [A. J. Garza, A. T. Bell, and M. Head-Gordon, ACS Catal. 2018, 8, 1490]. We also hypothesized that the third carbon atom in C₃ molecules is incorporated via a second C−C coupling reaction between a surface CO/CHO adsorbate and one C₂ intermediate that is already formed. Based on our calculations, the second C−C coupling reaction is also likely to occur prior to the above-mentioned branching point in an exergonic fashion so that its inclusion in the reaction network can significantly alter the previously modeled efficiency and selectivity of one-carbon (C₁) and C₂ products. Beyond deciphering the formation pathways of C₂ and C₃ species, our results also helped to provide a deeper mechanistic understanding of the CO₂RR catalyzed by metallic copper surfaces.