Reaction intermediates during operando electrocatalysis identified from full solvent quantum mechanics molecular...

Area of Science:

• Surface Chemistry
• Computational Chemistry
• Electrocatalysis

Background:

• Electrocatalysis enables selective molecular transformations but lacks mechanistic understanding at the electrode-electrolyte interface (EEI).
• Operando surface IR and Raman spectroscopy identify reaction intermediates but suffer from spectral noise, hindering atomistic structure determination.
• Bridging experimental limitations requires advanced computational methods to interpret operando spectroscopic data.

Purpose of the Study:

• To develop and apply a prototype operando quantum mechanics molecular dynamics (o-QM-MD) method for mechanistic studies.
• To characterize reactive intermediates in carbon dioxide reduction reactions (CO2RRs) under realistic operando conditions.
• To interpret experimental surface spectroscopy data and identify key intermediates.

Main Methods:

• Developed operando QM-MD (o-QM-MD) incorporating explicit solvent, EEI, and applied potential at 298 K.
• Characterized 22 potential reactive intermediates in CO2RRs using o-QM-MD.
• Calculated vibrational density of states (v-DoSs) using two-phase thermodynamic (2PT) analysis for spectral assignment.

Main Results:

• Identified key intermediates like *CO2, *HOC-COH, *C-CH, and *C-COH, correlating with experimental spectra.
• Assigned experimental peaks at 1,191 cm⁻¹ (C-O stretch in *HOC-COH) and 1,584 cm⁻¹ (C-C stretch in *C-COH).
• Discovered surface ketene (*C=C=O) formation via dehydration of *HOC-COH, suggesting a non-electrochemical hydrocarbon pathway.

Conclusions:

• o-QM-MD provides a powerful tool for interpreting operando spectroscopy and elucidating reaction mechanisms.
• The study successfully explains experimental observations in CO2RRs and identifies crucial intermediates.
• A novel non-electrochemical pathway for hydrocarbon formation via surface ketene was proposed under specific conditions.