Macromolecular design and synthesis of hydroxide conducting membranes with high alkaline stability
A3. Organic and Inorganic Ion Conducting MaterialsJoel Olsson1, Andrit Allushi1, Patric Jannasch1
1 Department of Chemistry, Lund University
Introduction/Purpose: Today extensive research efforts are devoted to the synthesis and studies of durable anion exchange membranes (AEMs) with the aim to develop alkaline fuel cells and electrolyzers that are able to operate efficiently without platinum group metal catalysts [1]. One of the great challenges is to design and synthesize polymeric AEM materials with high OH– conductivity and the necessary stability under highly alkaline conditions.
Methods: Previous studies of different small cationic model compounds have revealed that different alicyclic quaternary ammonium (QA) cations possess a very high alkaline stability [2]. Based on these findings, we have reported on AEMs based on poly(phenylene oxide) tethered with different alicyclic QA cations via flexible alkyl spacers [3]. Following a different approach, we have also designed, synthesized and studied polyelectrolytes containing N-spirocyclic cations, including poly(N,N-dimethylpiperidinium)s [4] and N-spirocyclic quaternary ammonium ionenes ("spiro-ionenes", Scheme 1) [5]. In addition, our group recently reported on the preparation and properties of poly(arylene piperidinium)s as a new class of high-performance AEM directly accessible using commercially available and quite inexpensive starting materials [6].
Results: AEMs incorporating alicyclic QA cations generally show very high alkaline and thermal stability, combined with high OH– conductivity. Still, the presence of diaryl ether linkages in the polymer backbone and the placement of QA cations in benzylic positions will induce alkaline degradation. Furthermore, the alkaline stability of the alicyclic QA cations in AEMs depend largely on attachment, ring size, and the presence of heteroatoms and substitution.
Conclusions: The overall results provide valuable insights towards the macromolecular design of highly thermochemically stable and hydroxide ion conductive AEMs for use in electrochemical devices operating under alkaline conditions.
Selected references
[1] M. A. Hickner, Electrochem. Soc. Interface 26 (2017) 69–73.
[2] M. G. Marino, K. D. Kreuer, ChemSusChem 8 (2015) 513–523.
[3] H. S. Dang, P. Jannasch, J. Mater. Chem. A 5 (2017) 21965–21978.
[4] J. S. Olsson, T. H. Pham, P. Jannasch, Macromolecules 50 (2017) 2784–2793.
[5] T. H. Pham, J. S. Olsson, P. Jannasch, J. Am. Chem. Soc. 139 (2017) 2888–2891.
[6] J. S. Olsson, T. H. Pham, P. Jannasch, Adv. Funct. Mater. 28 (2018) 1702758.
