ICS84

Synthesis and stability studies of N,N-diaryl-carbazolium salts for alkaline fuel cell applications

Nansi Gjineci 1 Sinai Aharonovich 1 Dario R. Dekel 2 Charles Diesendruck 1
1Schulich Faculty of Chemistry, Technion – Israel Institute of Technology, Haifa, Israel
2Wolfson Department of Chemical Engineering, Technion – Israel Institute of Technology, Haifa, Israel

The chemical stability of the cationic functional groups in Alkaline Anion-Exchange Membranes Fuel Cells (AEMFCs) is, currently, the critical challenge towards the development and commercialization of these devices1. Degradation of the cationic functional groups in the anion-exchange membranes leads to severe decrease in anion conductivity2. Therefore, novel chemistries and materials are necessary for the development of stable anion-exchange membranes with significantly improved lifetimes.

Tetraaryl ammonium salts possess structural features which can make them significantly more stable as compared to standard alkylammonium salts. Given all carbons connected to the nitrogen are sp2, SN2 reactions are inhibited. In addition, elimination reactions are also not favorable since the abstraction of a high energy benzynes. We will describe our work on the development of a simple synthesis procedure that, in only 3 steps, can lead to a variety of substituted N,N-diaryl carbazoliums salts3. In addition, we will show that, even with these structural features, we found that these quaternary ammonium salts decompose quite rapidly under the severe dry and alkaline conditions 4. Given these molecules can be further improved, we conducted a study using experimental measurements as well as DFT calculations to understand the mechanism of decomposition.

Based on these results, we have synthesized an additional series of carbazolium derivates with different electron donating substituents. We have compared their chemical stability in the presence of low hydration alkaline environment. Our results show a clear dependence between the strength of electron donating substituent and the chemical stability of the carbazolium salts. These new understandings bring a new light to the efforts to develop highly-stable anion-exchange membranes for fuel cell and other electrochemical applications5.

References

  1. Diesendruck, C.E. and Dekel D.R. Current opinion in electrochemistry, 2018, 9, 173-178.
  2. Dekel D.R. Journal of power sources, 2017, 375, 158-169.
  3. Aharonovich S., Gjineci N., Dekel D.R. and Diesendruck C.E. Synlett, 2018, 29 (10), 1314-1318.
  4. Dekel D.R., Amar M., Willdorf S., Kosa M., Dhara S. and Diesendruck C.E. Chemistry of Materials, 2017, 29, (10), 4425-4431.
  5. Dekel, R.D.; Diesendruck, C.E. patent pending.









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