Probing dissolved CO₂(aq) in aqueous solutions for CO₂ electroreduction and storage

Area of Science:

• Analytical Chemistry
• Electrochemistry
• Spectroscopy

Background:

• Dissolved carbon dioxide (CO2(aq)) is crucial for global warming mitigation strategies like CO2 capture and electroreduction.
• Accurate quantification of CO2(aq) is essential for optimizing these processes and for applications such as beverage analysis.
• Existing methods may lack the resolution or in situ capabilities for dynamic CO2(aq) measurements.

Purpose of the Study:

• To develop and validate a microscale infrared (IR) spectroscopy technique for in situ, dynamic quantification of CO2(aq).
• To derive an accurate molar extinction coefficient for CO2(aq) under high-pressure conditions.
• To investigate the kinetics and thermodynamics of CO2 dissolution and CO2 electroreduction (CO2RR).

Main Methods:

• Development of microscale IR spectroscopy for real-time analysis of CO2(aq).
• Observation of CO2(g) rotational state transitions and their quenching in aqueous solutions.
• Derivation of CO2 molar extinction coefficient (ε) up to 58 atm.
• In situ measurement of CO2(aq) concentrations in electrolytes under CO2(g) bubbling and high pressure.

Main Results:

• Quantified CO2(aq) concentrations in electrolytes with high spectral and time resolution.
• Observed quenching of CO2(g) rotational transitions and increased H2O IR absorption for CO2(aq).
• Achieved >98% Faradaic efficiencies for CO2 electroreduction to formate in KHCO3 electrolytes with high CO2(aq) concentrations (> ~1 M) using Cu2O/Cu electrocatalysts.
• Revealed significant hysteresis and ultraslow reversal in CO2(aq) supersaturation kinetics.

Conclusions:

• Microscale IR spectroscopy provides a powerful tool for in situ CO2(aq) quantification.
• High CO2(aq) concentrations enable efficient CO2 electroreduction to formate.
• The observed hysteresis and slow kinetics of CO2(aq) supersaturation have significant implications for CO2 capture and natural aquatic systems.