Nitrocellulose-Based Membranes for Electrocatalytic Bicarbonate-to-Formate Conversion via In Situ Generated CO₂

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Carbon dioxide (CO2) conversion via aqueous carbonate/bicarbonate solutions offers a promising pathway for reactive CO2 capture.
• Maintaining high Faradaic efficiency (FE) for CO2 electroreduction across varying pH levels presents a significant challenge.

Purpose of the Study:

• To investigate the role of a mixed cellulose ester (MCE) porous membrane in enhancing CO2 electroreduction efficiency.
• To evaluate the impact of different cellulose materials on formate production FE and electrolyzer performance at high current densities.

Main Methods:

• Electrolysis experiments utilizing a bismuth cathode, proton exchange membrane (PEM), and an intermediate MCE porous membrane.
• Performance evaluation across a broad pH range (up to 9.2) at current densities exceeding 100 mA cm-2.
• Operando electrochemical impedance spectroscopy (EIS) and real-time bubble formation visualization.

Main Results:

• The MCE membrane significantly enhanced formate FE, maintaining 78% at pH 9.2, by facilitating in situ CO2 (i-CO2) generation and utilization.
• Other cellulose materials (α-cellulose, acetyl cellulose) showed lower FE and higher cell resistance due to increased bubble formation.
• A system using 3.0 mol L-1 KOH for CO2 capture achieved 91% formate FE at 100 mA cm-2 with 80% i-CO2 utilization.

Conclusions:

• The MCE membrane, particularly its nitrocellulose component, is effective in sustaining i-CO2 generation and transport to the cathode.
• The MCE-based electrolyzer design demonstrates high potential for efficient reactive CO2 capture and utilization.
• Optimized MCE membrane integration can overcome pH limitations in electrochemical CO2 conversion.