Physical and Chemical Durability of Anion Exchange Membranes Used in the Electrochemical Reduction of CO 2

Membrane electrode assemblies (MEA) benefit from high current densities and FEs in the electrocatalytic CO 2 reduction reaction (CO 2 RR). However, membrane durability remains a challenge for industrial use. The aim of this study is to investigate the degradation mechanisms of three anion exchange membranes (AEMs) using 0.1M KHCO₃ electrolyte over a 250-hour CO 2 reduction period at 150 mA cm -2 . Three AEM materials were considered: FAA-3-50 (Fumatech), PiperION (Versogen), and Sustainion X37-50 (Dioxide Materials). Ex-situ investigations were carried out using techniques such as tensile testing, Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), and Electrochemical Impedance Spectroscopy (EIS) to evaluate chemical, electrical, and mechanical deterioration. Despite the use of the same near-nuetral KHCO 3 electrolytes, ATR-FTIR analysis showed different degradation patterns: nucleophilic substitution in FAA-3-50, Hoffman elimination in PiperION, and hydroxide-induced imidazolium breakage in Sustainion. According to EIS studies, the observed variation in ohmic resistance led to steady increases in cell potential increases from approximately 3.5 to 4.8 V at a current density of 150 mA cm -2 . HCO 3 ⁻ conductivity decreased by approximately 50% in the 250 hours of operation. Significant losses in mechanical integrity were also observed, including Young's modulus losses of 46% (FAA-3-50), 18% (PiperION), and 78% (Sustainion). The most notable increase in deformation at break was observed in Sustainion, which went from 4.8% to 20.46%, indicating a higher susceptibility to mechanical wear under prolonged use. This study shows that alkaline conditions in CO 2 reduction (including high local pH conditions near the cathode) cause AEM degradation, which in turn contributes to increases in cell potentials ranging from about 400 mV to 800 mV within several hundred hours of electrolysis at current densities in the range of 100 to 300 mA cm -2 .