Synthesis and Stability Measurements of N,N-Diarylcarbazolium Salts for Alkaline Fuel Cell Applications
2The Wolfson Faculty of Chemical Engineering, Technion-Israel Institute of Technology, Haifa, Israel
The chemical stability of the cationic functional groups in Alkaline Exchange Membranes Fuel Cells (AEMFCs) is the most critical limitation towards the commercialization of these devices1. Cationic degradation leads to decrease of membrane anion conductivity and in turn, to a rapid reduction of cell performance 2. Therefore, development of novel chemistries and new materials is necessary for the development of next generation of anion exchange membranes with increased durability.
Tetraaryl ammonium salts possess many structural advantages compared to other ammonium salts, either by inhibiting sites for SN2 reactions or by producing benzyne as a decomposition product, which is significantly higher in energy than a simple E2 reaction. Given the tetraphenylammonium salts are not synthetically available, we developed a simple approach to synthesize N,N-diphenylcarbazolium salts. Our synthesis requires only three steps and is based on the intramolecular cyclization of diazonium salts with tertiary amines3.
The characterization of the final carbazolium salt was carried out by NMR, MS, and X-ray crystallography, providing for the first time the solid-state structure of a tetraaryl ammonium salt. This structure showed extremely long C-N bonds. Different N,N-diarylcarbazolium salts were prepared and tested for their thermal and chemical stability. Degradation products were identified in order to further improve the kinetic stability of these salts.
(1) Gottesfeld, S.; Dekel, D. R.; Page, M.; Bae, C.; Yan, Y.; Zelenay, P.; Kim, Y. S. Anion Exchange Membrane Fuel Cells: Current Status and Remaining Challenges. J. Power Sources 2017, 1–15 DOI: 10.1016/j.jpowsour.2017.08.010.
(2) Dekel, D. R. Review of Cell Performance in Anion Exchange Membrane Fuel Cells. Journal of Power Sources. 2017.
(3) Aharonovich, S.; Gjineci, N.; Dekel, D. R.; Diesendruck, C. E. An Effective Synthesis of N,N-Diphenyl Carbazolium Salts. Aceepted to Synlett 2017.
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