Anion Exchange Membrane Transport and Accelerated Testing Methods for CO2 Electrolyzers with Cu-based Electrocatalyst

Electrocatalytic carbon dioxide (CO2) reduction to C2+ products holds promise for low carbon intensity fuels, chemicals, and food; however, durability challenges, particularly bicarbonate (HCO3-)and carbonate (CO32-) salt precipitation, hinder their commercialization. This report considers water (H2O) and ion transport properties of conventional anion exchange membranes (AEMs) in zero-gap membrane electrode assembly (MEA) configurations using Cu electrocatalysts. Transport characterization includes H2O diffusion, permeability, potassium (K+) diffusion, and transference numbers using three commercial AEMs, including piperidinium-based (Versogen), quaternary ammonium-based (Fumasep), and imidazolium-based (Dioxide Materials) membranes. Accelerated lifetime testing of CO2 reduction in MEA cells was conducted using galvanostatic stepping at 6-hour intervals to define a precipitation-free operating window. A “critical current density” was identified based on the cell potential and cathode pressure behaviors during the current density stepping experiments. When operating the MEA cell in a galvanostatic mode at the critical current density values, cathode drying and precipitation were observed within 100 hours of continuous electrolysis; however, operating the cell at a reduced level (75%) of the critical current extended continuous operation to 500 to 1000 hours or more.