Bipolar membrane electrolyzers enable high single-pass CO₂ electroreduction to multicarbon products

Area of Science:

• Electrochemistry
• Chemical Engineering
• Materials Science

Background:

• CO2 electrolysis faces energy penalties due to (bi)carbonate formation and crossover in alkaline/neutral media.
• Existing neutral-media electrolyzers are limited by a 25% single-pass CO2 utilization (SPU) for C2+ products.
• Downstream CO2 separation from anode gas outlets is energy-intensive.

Purpose of the Study:

• To develop a CO2 electrolyzer that overcomes the SPU limit and reduces CO2 separation energy penalties.
• To enable efficient in situ conversion of (bi)carbonate back to CO2 within the electrolyzer.
• To design and optimize a catholyte layer for enhanced CO2 conversion and product selectivity.

Main Methods:

• Utilizing a bipolar membrane (BPM) to manage (bi)carbonate conversion and prevent crossover.
• Employing a stationary unbuffered catholyte layer between the BPM and cathode.
• Developing a model to determine optimal catholyte layer diffusion path length (~10 μm).

Main Results:

• Achieved a single-pass CO2 utilization of 78%, surpassing the 25% SPU limit.
• Reduced the energy penalty associated with downstream CO2 separation by 10×.
• Demonstrated efficient in situ regeneration of CO2 from (bi)carbonate near the cathode.

Conclusions:

• The developed CO2 electrolyzer effectively converts (bi)carbonate back to CO2 using a BPM and optimized catholyte.
• This approach significantly enhances CO2 utilization and lowers energy consumption in CO2 electrolysis.
• The findings offer a pathway to more efficient and cost-effective CO2 conversion technologies.