(10b) Mechanistic Insights into C3 Products Formation from CO2 Electrocatalytic Reduction over Cu Electrodes

The selective and sustainable conversion of CO₂ into chemicals and fuels, especially through the electrochemical route (CO2RR), is important in CO₂ emissions reductions. Among many metals, copper has gained significant interest due to its unique ability to catalyze CO₂ reduction into multi-carbon (C₂₊) products. Unlike the main C₂ species like C₂H₄ and C₂H₅OH which are centers of many studies, much less is known about C₃ products, besides the fact that n-propanol is produced the most. The mechanism to form these species under the influence of electrochemical potentials, particularly the C-C coupling steps and the selectivity controlling factors, are still not fully explored. This limits further studies to enhance the production of n-propanol and C₃ products in general.

In this work, we examine the mechanism underlying the production of C₃ products in CO2RR. To properly account for the complex electrochemical metal/solution interface, we carried out ab initio molecular dynamics and potential-dependent density functional theory (DFT) simulations over the Cu(111) surface in the presence of explicit solvent and substrate molecules. The results are used to help elucidate different C-C coupling steps that lead to the C₃ products as a function of potentials. Our results suggest that the coupling steps are likely to occur between hydrocarbon fragments with CO*. The potential dependence of these coupling steps is discussed in the context of competing hydrogenation steps that dictate the selectivity of C₃ versus C₂ products. In addition, a possible path to form n-propanol, the most favored C₃ species, is presented together with mechanistic insights that determine the selectivity of n-propanol versus other C₃ species observed experimentally. Our findings advance the understanding that can aid further designs of electrodes for enhanced C₃ productions.