Diagnosing mechanisms to mitigate anion exchange ionomer degradation during impure water electrolysis

Abstract

Anion exchange membrane water electrolyzers (AEMWEs) promise a route to produce low-cost H₂; however, the durability of AEMs can be hindered by ionomer degradation and water feedstock impurities. Herein, we evaluated chemical and electrochemical degradation pathways of PiperION, a common anionic ionomer, under anodic and chemically oxidizing conditions in an saline electrolyte (0.5 M NaCl). Based on X-ray photoelectron spectroscopy and electrochemical mass spectrometry data, we propose two degradation pathways: radical-mediated ionomer oxidation and chemically-mediated chlorination of the polymer backbone. We assigned the formation of C–Cl covalent bonds on the PiperION backbone to free chlorine formation under anodic electrochemical conditions in the presence of Cl⁻. Ionomer oxidation characterized by formation of C–O/CO bonds and CO₂ generation was substantially suppressed by using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), which may act as a radical scavenger. These findings provide insight into improving the resilience of anion-exchange ionomers and designing AEMWE technologies robust to variable operation expected over long-term deployment.