Efficient Bicarbonate Electrolysis to Formate Enabled via Ionomer Surface Modification in Cation Exchange Membrane Electrolyzers

Abstract

Abstract Electrochemical CO 2 reduction (CO 2 RR) is a promising method for converting CO 2 into valuable chemicals, with formate being a particularly viable product. However, current gas‐fed CO 2 RR systems rely on highly pure CO 2 feed gases and are incompatible with point‐source CO 2 emissions without prior capture and concentration. Bicarbonate electrolysis offers a potential solution by bridging the gap between CO 2 emissions and utilization. However, existing electrolyzer configurations, especially those using bipolar membranes (BPM), require high working voltages and suffer from poor energy efficiency. Here, we present a cation exchange membrane (CEM)‐based membrane electrode assembly (MEA) incorporating a surface‐modified bismuth cathode catalyst. The success of this approach is attributed to two key factors: the use of the positively charged ionomer PiperION for surface modification, which creates a favorable cathode microenvironment; the single CEM that enhances proton flux from the anode to the cathode while reducing ionic impedance. The CEM‐based MEA demonstrates a formate faradaic efficiency of up to 80%, with a significant 1.5 V reduction in operating voltage compared to BPM‐based MEAs at 300 mA cm −2 . Additionally, the CEM‐based MEA exhibits excellent tolerance to O 2 impurities and maintains high performance even with simulated flue gas, making it suitable for direct CO 2 utilization from point sources.