The electrochemical reduction of CO(2) 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 im proved substantially in the last decade, they still suffer from poor selectivity towards the most desired products, ethylene and ethanol. This is in part due to the fact that a detailed mechanistic understanding of the selectivity towards 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 CO(2) electroreduction on Cu towards the major multi-carbon 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 towards 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 towards the specific products. Our study paves the way for the design of efficient CO2 electrolyzers for the production of targeted multi-carbon products, thereby moving a step closer towards their widespread adaptation.
Computational details, Illustration of intermediate structures noted in figure 1, Detailed stepwise kinetic study, Free energy diagram at COR reaction conditions, Degree of selectivity control analysis, Derivation of the potential and pH response for specific products, Elementary step towards acetaldehyde, Overall turnover frequency to C2+ products, BEP relations and intrinsic reaction barriers at pH 7, Experimental potential response within CO2R and COR, Re-evaluation of Hori’s measurements, Potential response of reaction intermediates, Imaginary frequencies of transition states