Decomposition pathways of an alkaline fuel cell membrane material component via evolved gas analysis

Abstract

The mechanism of the thermal decomposition of [NMe₄][OH]·5H₂O, tetramethyl ammonium hydroxide pentahydrate, was studied using DSC, TG and evolved gas analysis because of the importance of related ions in anion exchange membranes. The products of the reaction are trimethyl amine, methanol and dimethyl ether. The relative ratio of the products is determined by how much water remains in the sample as it is decomposing. Isotopic labeling experiments with D₂O show that deprotonation of the tetramethyl ammonium ion by hydroxide establishes a rapid equilibrium between tetramethyl ammonium ion and the nitrogen ylide species and water that scrambles the deuterium with the proton in the methyl groups. The results of this work also suggest that tetraalkyl ammonium cations may be more stable in hydroxide conducting membranes than previously believed.