(695b) CO2 Reduction on Copper: Mechanistic Analysis from Accurate Electronic Structure Methods.

Electrochemical carbon dioxide reduction (CO₂R) could contribute to a circular economy that will curtail unsustainable fossil fuel burning and decrease future greenhouse gas emissions. The lack of practical electrocatalysts impedes its further development. Rational design of efficient, selective CO₂R electrocatalysts necessitates a reliable mechanistic analysis on the most efficacious catalysts thus far identified, namely, copper (Cu). Because in situ electrochemical mechanism determination by experimental techniques remains out of reach, such mechanistic analysis typically is conducted using density functional theory (DFT). However, the DFT exchange-correlation approximations most often used to model such reactions unfortunately engender a foundational error, predicting the wrong adsorption site for CO (a key CO₂R intermediate) on metal surfaces (including Cu), casting doubt on previous DFT-predicted CO₂R kinetics. Our work rigorously elucidates reaction mechanisms involved in electrochemical CO₂R on Cu, by means of state-of-the-art embedded correlated wavefunction theory, which corrects for exchange-correlation errors inherent in conventional DFT approximations. We examine competing carbon monoxide reduction steps via proton-coupled electron transfer path and multiple C-C coupling steps towards generation of multi-carbon hydrocarbon products. We show for the first time on a practical electrocatalyst how crucial it can be to use advanced theory that goes beyond standard DFT to properly describe rate-limiting steps in electrochemistry. Our study inspires new design principles for CO₂R electrocatalysts with enhanced activity and selectivity.