Revisiting Competing Paths in Electrochemical CO₂ Reduction on Copper via Embedded Correlated Wavefunction Theory

Area of Science:

• Computational Chemistry
• Surface Science
• Catalysis

Background:

• Copper is a key catalyst for CO2 reduction, but its reaction mechanisms are not fully understood.
• Density functional theory (DFT) approximations can introduce errors in predicting reaction pathways.
• Higher-level theories are needed to accurately describe electronic structures and energetics in catalytic processes.

Purpose of the Study:

• To re-evaluate critical steps in CO2 reduction on copper using embedded correlated wavefunction (ECW) theory.
• To investigate the initial CO reduction step on the Cu(111) surface and its implications for reaction selectivity.
• To compare mechanistic predictions from DFT and ECW theory.

Main Methods:

• Employed density functional embedding theory (DFET) to optimize embedding potentials at the DFT level.
• Screened adsorption sites using ECW theory to refine local electronic structure.
• Determined minimum energy reaction pathways using the climbing-image nudged elastic band method at the DFT level, with energetics corrected by ECW calculations.

Main Results:

• ECW theory predicts different adsorption site preferences compared to DFT due to DFT's limitations in describing the CO 2π* level.
• Confirmed that the initial step in CO reduction via hydrogen transfer on Cu(111) forms hydroxymethylidyne (*COH), not formyl (*CHO).
• While the preferential formation of *COH is consistent between DFT and ECW theory, significant differences in structural and mechanistic details were observed.

Conclusions:

• ECW theory provides a more accurate description of CO2 reduction mechanisms on copper surfaces.
• The study highlights the necessity of advanced theoretical methods to resolve discrepancies with DFT predictions.
• Further investigation is required to fully elucidate the CO2 reduction mechanism, with ongoing work planned.