Baseline BTMA Degradation as a Standard for Cationic Degradation in AEMFCs

Alkaline membranes are of high interest as hydroxide conducting polymers in electrochemical devices. Benzyltrimethylammonium (BTMA) has historically been the cation most often employed in anion exchange membranes. Fuel cell literature often compares cation stabilities under alkaline conditions to that of BTMA. However throughout the literature each study employs a different experimental method when determining these stabilities. This variety of methods makes cross comparisons of novel cations difficult if at all possible. Additionally, we have found that several methods reported have inherent flaws in their findings due to the difficulty of performing stability experiments with high base concentrations. Herein we report a reliable, standardized method of determining cation stability under alkaline conditions that mimic those expected under operating conditions of electrochemical devices. During development, several common experimental pitfalls are addressed and avoided. The standardized method has been employed to determine BTMA stabilities at varying concentrations (0.01, 0.1, and 0.5 M BTMA) at 120, 140 and 160 °C in 2 M KOH in H₂O, and have found BTMA to be very stable at 80 °C.