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Exploring N-alicyclic quaternary ammonium functional polymers as hydroxide exchange membranes

Olsson, Joel LU (2020)
Abstract
As the global power generation is shifted toward renewable and intermittent sources, the importance of fuel cells and other energy storage and conversion devices is continually increasing. However, many of these technologies are still under development and further research is necessary before they can be implemented. This is the case for the hydroxide exchange membrane fuel cell (HEMFC), which has been identified as an important next-generation conversion technology. One under-developed and critical component of this technology, which is currently hampering its application, is the hydroxide exchange membrane (HEM). It consists of cationic polymers that conduct hydroxide ions and is essential to the performance and durability of the fuel... (More)
As the global power generation is shifted toward renewable and intermittent sources, the importance of fuel cells and other energy storage and conversion devices is continually increasing. However, many of these technologies are still under development and further research is necessary before they can be implemented. This is the case for the hydroxide exchange membrane fuel cell (HEMFC), which has been identified as an important next-generation conversion technology. One under-developed and critical component of this technology, which is currently hampering its application, is the hydroxide exchange membrane (HEM). It consists of cationic polymers that conduct hydroxide ions and is essential to the performance and durability of the fuel cell. During prolonged fuel cell operation current HEMs tend to degrade due to an incompatibility between the cationic polymers and the hydroxide ions. To overcome this, continued exploration of new polymer architectures and chemistries is needed and that is where this thesis work comes in.
In this work, we have designed and synthesized different cationic polymers functionalized with N-alicyclic quaternary ammonium (QA) cations for use as HEMs. The overall focus of this thesis has been to explore the effect of different structural elements of the polymers, such as cation design and placement, on key properties of the HEMs. While extra emphasis was placed on the alkaline stability of the polymers, other ex-situ properties such as hydroxide conductivity, water uptake, morphology and thermal stability has also been studied. The scientific approach was constructed to highlight important structure-property relationships and gain other valuable insights that might aid the ongoing and future research on HEMs and HEMFCs.
The investigated polymers include poly(diallylammonium hydroxide)s prepared in radical initiated cyclopolymerizations, poly(arylene piperidinium)s prepared in superacid promoted Friedel-Crafts polycondensations and polystyrene functionalized in hydroxyalkylation reactions. HEMs with high hydroxide conductivity (>100 mS cm-1) was obtained from all these polymers. A general finding observed while studying these materials was that the stability of N-alicyclic QA cations is very dependent on the conformational freedom of the ring. In contrast to studies on model compounds, when incorporated into a polymer the N-spirocyclic cation was consistently observed to be less stable than the monocyclic N,N-dimethylpiperidinium cation, and main pathway of degradation for both ions was via ring-opening β-hydrogen elimination.
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author
supervisor
opponent
  • Ass. Prof. Ghislain, David, University of Montpellier, France.
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Electrolyte membrane, Anion exchange membranes, Anion exchange membrane fuel cells, Structure-property relationship, Quaternary ammonium cations, Alkaline stability, Synthesis, Characterization
pages
215 pages
publisher
Centre for Analysis and Synthesis
defense location
Lecture hall KC:C, Kemicentrum, Naturvetarvägen 14, Faculty of Engineering LTH, Lund University, Lund. Follow online: http://www.kilu.lu.se/cas/calendar/?event=dissertation-joel-olsson
defense date
2020-05-08 13:00:00
ISBN
978-91-7422-738-3
978-91-7422-739-0
language
English
LU publication?
yes
id
80074e3b-bae2-4830-9828-bdf0f158582d
date added to LUP
2020-04-06 16:33:48
date last changed
2020-04-16 10:03:39
@phdthesis{80074e3b-bae2-4830-9828-bdf0f158582d,
  abstract     = {As the global power generation is shifted toward renewable and intermittent sources, the importance of fuel cells and other energy storage and conversion devices is continually increasing. However, many of these technologies are still under development and further research is necessary before they can be implemented. This is the case for the hydroxide exchange membrane fuel cell (HEMFC), which has been identified as an important next-generation conversion technology. One under-developed and critical component of this technology, which is currently hampering its application, is the hydroxide exchange membrane (HEM). It consists of cationic polymers that conduct hydroxide ions and is essential to the performance and durability of the fuel cell. During prolonged fuel cell operation current HEMs tend to degrade due to an incompatibility between the cationic polymers and the hydroxide ions. To overcome this, continued exploration of new polymer architectures and chemistries is needed and that is where this thesis work comes in. <br/>In this work, we have designed and synthesized different cationic polymers functionalized with <i>N</i>-alicyclic quaternary ammonium (QA) cations for use as HEMs. The overall focus of this thesis has been to explore the effect of different structural elements of the polymers, such as cation design and placement, on key properties of the HEMs. While extra emphasis was placed on the alkaline stability of the polymers, other ex-situ properties such as hydroxide conductivity, water uptake, morphology and thermal stability has also been studied. The scientific approach was constructed to highlight important structure-property relationships and gain other valuable insights that might aid the ongoing and future research on HEMs and HEMFCs.<br/>The investigated polymers include poly(diallylammonium hydroxide)s prepared in radical initiated cyclopolymerizations, poly(arylene piperidinium)s prepared in superacid promoted Friedel-Crafts polycondensations and polystyrene functionalized in hydroxyalkylation reactions. HEMs with high hydroxide conductivity (&gt;100 mS cm<sup>-1</sup>) was obtained from all these polymers. A general finding observed while studying these materials was that the stability of <i>N</i>-alicyclic QA cations is very dependent on the conformational freedom of the ring. In contrast to studies on model compounds, when incorporated into a polymer the <i>N</i>-spirocyclic cation was consistently observed to be less stable than the monocyclic <i>N</i>,<i>N</i>-dimethylpiperidinium cation, and main pathway of degradation for both ions was via ring-opening β-hydrogen elimination.<br/>},
  author       = {Olsson, Joel},
  isbn         = {978-91-7422-738-3},
  language     = {eng},
  publisher    = {Centre for Analysis and Synthesis},
  school       = {Lund University},
  title        = {Exploring <i>N</i>-alicyclic quaternary ammonium functional polymers as hydroxide exchange membranes},
  url          = {https://lup.lub.lu.se/search/ws/files/78157712/Thesis_J.S.Olsson.pdf},
  year         = {2020},
}