Combining First-Principles Kinetics and Experimental Data to Establish Guidelines for Product Selectivity in Electrochemical CO2 Reduction

The electrochemical reduction of CO2 is envisioned as one of the most promising ways to close the industrial carbon cycle by producing high-value chemicals and fuels using renewable electricity. Although the performance of CO2 electrolyzers has improved substantially in the past decade, they still suffer from poor selectivity toward the most desired products, ethylene and ethanol. This is in part due to the fact that a detailed mechanistic understanding of the selectivity toward various products is still lacking, although such an understanding is essential for process optimization. Herein, we perform microkinetic simulations based on constant-potential density functional theory to elucidate the reaction pathways for CO2 electroreduction on Cu(100) toward the major multicarbon products. We find that ethylene is the first product that bifurcates from the oxygenates, followed by acetate. Acetaldehyde is a direct intermediate in the production of ethanol. We provide atomistic level insights on the major role played by the electrode potential and electrolyte pH in determining the selectivity toward ethylene, oxygenates, and methane and relate the origin of the selectivity to general trends in electrochemical reaction energetics. We verify the results of our microkinetic simulations to an experimental database of previously reported measurements. Finally, we suggest guidelines for improving the selectivity toward the specific products. Our study paves the way for the design of efficient CO2 electrolyzers for the production of targeted multicarbon products, thereby moving a step closer toward their widespread adaptation.