Enriching Surface-Accessible CO₂ in the Zero-Gap Anion-Exchange-Membrane-Based CO₂ Electrolyzer

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Anion exchange membrane (AEM)-based CO2 electrolysis offers a pathway for CO production.
• Performance limitations at high current densities are linked to low local CO2 concentrations caused by CO2 neutralization.

Purpose of the Study:

• To develop a descriptor, surface-accessible CO2 concentration ([CO2]SA), to quantify local CO2 availability.
• To identify strategies for enhancing [CO2]SA and improving CO2 electrolysis performance.

Main Methods:

• Utilized mass transport modeling to analyze CO2 utilization.
• Investigated CO2 feed mode modulation.
• Developed and tested strategies including catalyst layer thickness, CO2 pressure, and pulsed electrochemical (PE) methods.

Main Results:

• Introduced the [CO2]SA descriptor to indicate the transient local [CO2]/[OH-] ratio.
• Demonstrated that increasing catalyst layer thickness, CO2 pressure, or applying a PE method can enrich [CO2]SA.
• An optimized PE method maintained high [CO2]SA by leveraging the CO2 neutralization dynamic balance period.

Conclusions:

• The [CO2]SA descriptor is crucial for defining CO2-to-CO conversion limits.
• The PE method is effective in enhancing CO2 accessibility and performance.
• Achieved a maximum CO current density (jCO) of 368±28 mA cm-2 using a commercial silver catalyst.