The Electrode/Electrolyte Interface Study during the Electrochemical CO₂ Reduction in Acidic Electrolytes.

Area of Science:

• Electrochemistry
• Surface Science
• Catalysis

Background:

• Electrochemical CO2 Reduction (CO2R) in acidic electrolytes offers advantages in efficiency and stability over alkaline systems.
• The precise proton source and the function of alkali cations in acidic CO2R remain incompletely understood.
• Clarifying interfacial conditions is crucial for advancing CO2R technology.

Purpose of the Study:

• To elucidate the interfacial conditions necessary for CO2R in acidic electrolytes.
• To identify the true proton source and the role of alkali cations during CO2R.
• To determine the active CO2 species involved in the reaction.

Main Methods:

• Utilized rotating ring disk electrode (RRDE) voltammetry to probe reaction mechanisms.
• Employed surface-enhanced infrared absorption spectroscopy (SEIRAS) for in-situ interfacial analysis.
• Investigated the influence of electrolyte composition and electrode potential on CO2R.

Main Results:

• Confirmed that a neutral to alkaline microenvironment at the electrode-electrolyte interface is essential for CO2R, irrespective of bulk electrolyte acidity.
• Demonstrated that water molecules, not bulk protons, serve as the proton source for CO2 reduction.
• Showed that alkali cations in the outer Helmholtz plane facilitate H2O activation and suppress CO poisoning by promoting CO desorption.
• Identified solvated CO2 (CO2(aq)) as the reactive species, not dissolved CO2 gas.

Conclusions:

• The study reveals that interfacial pH control is critical for efficient electrochemical CO2 reduction in acidic media.
• Water acts as the proton donor, and alkali cations play a key catalytic role.
• Understanding these interfacial phenomena provides a pathway for optimizing CO2R systems for carbon capture and utilization.