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Aromatic Polymers Functionalized with Anionic and Cationic Groups for Ion Exchange Membranes

Weiber, Annika LU (2015)
Abstract
Fuel cells, redox flow batteries and some water desalination technologies such as reverse osmosis and electrodialysis require efficient ion exchange membranes to perform in an optimum way. Thus, by enhancing the properties of these membranes there is a possibility to improve this type of applications and technologies. Depending on the specific application, anion or proton exchange membranes with good thermal, chemical and mechanical stability combined with an efficient ion transport are sought for. In the current study, the effect of local ion concentration on properties such as water uptake and ion conductivity was investigated. This was done by systematically controlling the local density of ionic groups. When four instead of two... (More)
Fuel cells, redox flow batteries and some water desalination technologies such as reverse osmosis and electrodialysis require efficient ion exchange membranes to perform in an optimum way. Thus, by enhancing the properties of these membranes there is a possibility to improve this type of applications and technologies. Depending on the specific application, anion or proton exchange membranes with good thermal, chemical and mechanical stability combined with an efficient ion transport are sought for. In the current study, the effect of local ion concentration on properties such as water uptake and ion conductivity was investigated. This was done by systematically controlling the local density of ionic groups. When four instead of two sulfonic acid groups were located on neighbouring aromatic rings on a polysulfone backbone, the proton conductivity under reduced relative humidity was significantly increased. A correlation between distinctive ion clustering, reduced water uptake and an increase in ion conductivity was observed when the stiffness of the polymer backbone was increased by the replacement of the flexible ether bridges in the polymer structure by stiffer sulfone bridges. Anion exchange materials are less prone to form ion clusters. To study this, polymers with a well-controlled local ion density were synthesized. The ion concentration was varied from being random to a placement of the ions in pairs, triplets and quartets. This allowed for a systematic study of the effect of ion distribution and a high local ion concentration was observed to promote ionic clustering. However, a reduction in ion conductivity was also seen as a result of high local ion concentration, probably due to the formation of ion condensates. In order to be able to use anion exchange membranes in fuel cells they need to withstand a highly alkaline environment. This was not the case for the polysulfone-based materials, thus a material with poly(2,6-dimethyl-1,4-phenylene oxide) as polymer backbone was produced. In this case, the cationic groups were distanced from the polymer backbone by a flexible aliphatic spacer. This did not only allow for an enhancement of the ion conductivity, but also a significant increase in the stability under alkaline conditions, thus making it an interesting material for further analysis and development. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof. Varcoe, John R., University of Surrey, United Kingdom
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Ion exchange membranes, fuel cells, polycondensation, local ion density, poly(arylene ether sulfone)s
pages
182 pages
defense location
Lecture hall B, Kemicentrum, Getingev├Ągen 60, Lund University, Faculty of Engineering LTH, Lund
defense date
2015-09-04 10:15
ISBN
978-91-7422-404-7
language
English
LU publication?
yes
id
a62dfb20-a919-49d0-ab83-ce05d824b98e (old id 5470755)
date added to LUP
2015-06-11 10:57:42
date last changed
2016-09-19 08:45:19
@phdthesis{a62dfb20-a919-49d0-ab83-ce05d824b98e,
  abstract     = {Fuel cells, redox flow batteries and some water desalination technologies such as reverse osmosis and electrodialysis require efficient ion exchange membranes to perform in an optimum way. Thus, by enhancing the properties of these membranes there is a possibility to improve this type of applications and technologies. Depending on the specific application, anion or proton exchange membranes with good thermal, chemical and mechanical stability combined with an efficient ion transport are sought for. In the current study, the effect of local ion concentration on properties such as water uptake and ion conductivity was investigated. This was done by systematically controlling the local density of ionic groups. When four instead of two sulfonic acid groups were located on neighbouring aromatic rings on a polysulfone backbone, the proton conductivity under reduced relative humidity was significantly increased. A correlation between distinctive ion clustering, reduced water uptake and an increase in ion conductivity was observed when the stiffness of the polymer backbone was increased by the replacement of the flexible ether bridges in the polymer structure by stiffer sulfone bridges. Anion exchange materials are less prone to form ion clusters. To study this, polymers with a well-controlled local ion density were synthesized. The ion concentration was varied from being random to a placement of the ions in pairs, triplets and quartets. This allowed for a systematic study of the effect of ion distribution and a high local ion concentration was observed to promote ionic clustering. However, a reduction in ion conductivity was also seen as a result of high local ion concentration, probably due to the formation of ion condensates. In order to be able to use anion exchange membranes in fuel cells they need to withstand a highly alkaline environment. This was not the case for the polysulfone-based materials, thus a material with poly(2,6-dimethyl-1,4-phenylene oxide) as polymer backbone was produced. In this case, the cationic groups were distanced from the polymer backbone by a flexible aliphatic spacer. This did not only allow for an enhancement of the ion conductivity, but also a significant increase in the stability under alkaline conditions, thus making it an interesting material for further analysis and development.},
  author       = {Weiber, Annika},
  isbn         = {978-91-7422-404-7},
  keyword      = {Ion exchange membranes,fuel cells,polycondensation,local ion density,poly(arylene ether sulfone)s},
  language     = {eng},
  pages        = {182},
  school       = {Lund University},
  title        = {Aromatic Polymers Functionalized with Anionic and Cationic Groups for Ion Exchange Membranes},
  year         = {2015},
}