The Solvation-Induced Onsager Reaction Field Rather than the Double-Layer Field Controls CO₂ Reduction on Gold

Area of Science:

• Electrochemistry
• Catalysis
• Surface Science

Background:

• Electrolyte cations influence the selectivity and activity of carbon dioxide reduction (CO2R).
• Understanding the electric field at catalytic sites is key to optimizing CO2R.
• Previous theoretical models may not fully capture the interfacial dynamics.

Purpose of the Study:

• To quantify the electric field contributions at catalytic sites during CO2R.
• To determine the role of the Stern and Onsager fields in CO2R kinetics.
• To investigate the influence of interfacial solvation and cation structure on CO2R.

Main Methods:

• In situ vibrational Stark shift spectroscopy to measure electric fields on gold (Au) catalysts.
• Analysis of alkali cation effects on the CO2R reaction.
• Vibrational sum frequency generation (VSFG) spectroscopy to study interfacial water structure.

Main Results:

• CO2R kinetics correlate with the Onsager (solvation-induced) reaction field, not the Stern field.
• The Onsager field dominates over the Stern field in the presence of adsorbed CO2, driving CO2 activation.
• Cation-dependent interfacial water structure strongly influences CO2R activity.

Conclusions:

• The Onsager reaction field is the primary driver of CO2R kinetics, contrary to some theoretical predictions.
• Accurate understanding of CO2R requires explicit consideration of cation-dependent interfacial water structure and its electric field.
• Optimizing CO2R catalysts necessitates controlling interfacial solvation effects.