Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO₂ Reduction

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Electrochemical CO2 reduction (CO2 R) to chemical feedstocks faces challenges in achieving high product selectivity.
• Silver (Ag) is a promising catalyst for CO2 R, but optimizing its performance is crucial for industrial viability.

Purpose of the Study:

• To investigate the effect of reline (choline chloride + urea) on the selectivity of electrochemical CO2 reduction using Ag foil cathodes.
• To understand the surface interactions and mechanisms responsible for enhanced CO2 to CO conversion.

Main Methods:

• Electrochemical CO2 reduction experiments were conducted using Ag foil cathodes in 50 wt% aqueous reline.
• Cathode surface restructuring involved oxide layer dissolution and electrodeposition of Ag nanoparticles.
• Surface analysis techniques were employed to characterize the modified Ag surface and adsorbed species.

Main Results:

• Achieved highly selective CO2 R to CO with a faradaic efficiency of (96±8)% at -0.884 V vs. the reversible hydrogen electrode (RHE).
• Demonstrated a 1.5-fold improvement in selectivity compared to CO2 R in KHCO3.
• Observed surface restructuring of Ag foil, exposing low-coordinated Ag atoms and stabilizing key intermediates (*COOH) via adsorption of choline ions and urea.

Conclusions:

• Interactions between Ag cathodes and reline significantly enhance selectivity for CO2 to CO reduction.
• Surface restructuring and specific ion adsorption play a critical role in stabilizing intermediates and improving catalytic performance.
• The developed approach shows potential for extension to other electrocatalytic metals and deep eutectic solvents for continuous-flow CO2 R.