Understanding Limitations in Electrochemical Conversion to CO at Low CO₂ Concentrations

Area of Science:

• Electrochemistry
• Catalysis
• Carbon Capture and Utilization

Background:

• Low-temperature electrochemical reduction of carbon dioxide (CO2) shows high carbon monoxide (CO) selectivity with pure CO2 streams.
• Limited understanding exists for CO2 reduction at concentrations below 30%, crucial for integrating with industrial CO2 point sources.

Purpose of the Study:

• To investigate the impact of ionomer chemistry and operating conditions on CO selectivity during electrochemical CO2 reduction at low CO2 concentrations.
• To correlate electrochemical diagnostics of cathode properties with CO selectivity and catalyst utilization.

Main Methods:

• Advanced electrochemical diagnostics were employed to measure cathode catalyst layer ionic resistance and electrocatalyst capacitance.
• Measurements were performed as a function of relative humidity (RH) and CO2 concentration.
• CO selectivity and catalyst utilization were analyzed under varying conditions.

Main Results:

• High CO/H2 selectivity (>95%) was maintained at CO2 concentrations above 20% with at least 50% cathode RH, irrespective of ionomer type.
• At 10% CO2 concentration, achieving >95% CO/H2 selectivity necessitated 95% RH and electrode morphologies that facilitated high catalyst utilization.

Conclusions:

• Maintaining adequate relative humidity and CO2 concentration is critical for selective electrochemical CO2 to CO conversion.
• Electrode design and morphology play a significant role in achieving high selectivity at very low CO2 concentrations, highlighting the importance of optimizing catalyst utilization.