Computational Modeling of Degradation of Substituted Benzyltrimethyl Ammonium

The stability of cations used in the alkaline exchange membranes has been a major challenge for alkaline membrane fuel cells. In this paper, the degradation barriers were investigated by density functional theory for substituted benzyltrimethyl ammonium (BTMA⁺) cations. BTMA⁺ is one of the most commonly used cations for alkaline exchange membranes. It was found that substituted cations with electron-donating substituent groups at meta-position of the benzyl ring could result in improved degradation barriers. However, after investigating more than thirty substituted BTMA⁺ cations with ten different substituent groups, the largest improvement of degradation barriers calculated was only 1.6 kcal/mol. While this may be a meaningful increase in stability for some applications, it suggests that only a modest improvement in stability is possible through substitution of BTMA⁺.