Spatial reactant distribution in CO₂ electrolysis: balancing CO₂ utilization and faradaic efficiency

Area of Science:

• Electrochemistry
• Chemical Engineering
• Materials Science

Background:

• CO2 electrolyzers show promise for producing value-added C1 and C2 compounds.
• Catalytic performance is advancing, shifting focus to system-level CO2 utilization and efficiency.

Purpose of the Study:

• To investigate the trade-offs between CO2 utilization and electrolyzer performance, specifically faradaic efficiency, as a function of CO2 availability.
• To provide a spatially resolved understanding of product selectivity within CO2 electrolyzers.

Main Methods:

• Combined experimental and 3D modeling approach.
• Operated a membrane-electrode assembly CO2 electrolyzer at 200 mA cm-2 with varying inlet flow rates.
• Analyzed spatial variations in CO2 concentration and their effect on faradaic efficiency.

Main Results:

• Demonstrated spatial variations in faradaic efficiency due to non-uniform CO2 concentration, unobservable with 'black box' methods.
• Observed faradaic efficiency losses even at 80% CO2 consumption.
• Modeling indicated avoidable H2 generation linked to flow field design.

Conclusions:

• Spatially resolved analysis is crucial for understanding CO2 electrolyzer performance.
• Optimizing flow field design can mitigate efficiency losses and improve CO2 utilization.
• Findings provide foundational design rules for balancing CO2 utilization and device performance.