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

Authors: 
Lin, Z., University of California - Berkeley
Jiang, K., Rowland Institute at Harvard, Harvard University
Garza, A. J., The Dow Chemical Company
Bell, A. T., University of California
Head-Gordon, M., University of California - Berkeley
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.