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

Electrochemical CO2 reduction (CO2RR) is a promising method for converting CO2 into valuable chemicals, with formate being a particularly viable product. However, current gas‐fed CO2RR systems rely on highly pure CO2 feed gases and are incompatible with point‐source CO2 emissions without prior capture and concentration. Bicarbonate electrolysis offers a potential solution by bridging the gap between CO2 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 V reduction in operating voltage compared to BPM‐based MEAs at 300 mA cm‐2. Additionally, the CEM‐based MEA exhibits excellent tolerance to O2 impurities and maintains high performance even with simulated flue gas, making it suitable for direct CO2 utilization from point‐source.