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Intrinsically Proton-Conducting Benzimidazole Units Tethered to Different Polymer Chain Architectures

Persson, Christian LU (2005)
Abstract (Swedish)
Popular Abstract in Swedish

Protontransport är en fundamental process som finns i många naturliga system, liksom i många tekniska applikationer, såsom bränsleceller, smarta fönster och olika typer av sensorer. Bränslecellsteknologi anses vara miljövänlig eftersom bränsleceller inte begränsas av Carnot-cykeln och omvandlar effektivt kemisk energi till elektrisk energi som sedan kan användas till att driva till exempel bilar, bärbara datorer eller byggnader. En av de mest lovande bränslecellerna för användning i portabla applikationer är polymerelektrolyt-bränslecellen (PEMFC). Kommersialiseringen av PEMFC begränsas dock av olika faktorer, bland annat av de otillräckliga egenskaperna hos polymermembranet vid temperaturer över... (More)
Popular Abstract in Swedish

Protontransport är en fundamental process som finns i många naturliga system, liksom i många tekniska applikationer, såsom bränsleceller, smarta fönster och olika typer av sensorer. Bränslecellsteknologi anses vara miljövänlig eftersom bränsleceller inte begränsas av Carnot-cykeln och omvandlar effektivt kemisk energi till elektrisk energi som sedan kan användas till att driva till exempel bilar, bärbara datorer eller byggnader. En av de mest lovande bränslecellerna för användning i portabla applikationer är polymerelektrolyt-bränslecellen (PEMFC). Kommersialiseringen av PEMFC begränsas dock av olika faktorer, bland annat av de otillräckliga egenskaperna hos polymermembranet vid temperaturer över 100 ºC. Detta beror på att membranet måste innehålla vatten för att uppnå hög protonledning. Genom att köra bränslecellen vid högre temperaturer (150-200 ºC), kan många fördelar uppnås på systemnivå.



Följdaktligen prövades konceptet med fullständigt polymera protonledare där protonbärarna ympades på olika polymerkedjor för att undvika förluster av protonbärare vid höga temperaturer. I detta fall valdes benzimidazol som protonbärare på grund av dess naturliga förmåga att leda protoner och dess goda kemiska och termiska stabilitet. En serie med modelmaterial bestående av polymerer med olika struktur och arkitetktur och med påympade benzimidazolenheter syntetiserades och studerades med avseende på protonledning. Ett modulärt syntesschema för att införliva benzimidazolenheter i polymerer via tiol-en koppling utvecklades. Generellt ökade glasövergångstemperaturen med ökande benzimidazolkoncentration, vilket indikerade att de polymera segmentrörelserna undertrycktes. Denna effekt tillskrevs de starka vätebindningarna mellan benzimidazolenheterna. När längden på sidokedjorna ökades, frikopplades benzimidazolen från segmentrörelserna hos polymeren. Benzimidazolkoncentrationen och segmentrörligheten var de viktigaste parametrarna för att uppnå hög protonledning, oavsett polymerarkitekturen. Konduktiviteten främjades av hög benzimidazolkoncentration och hög segmentrörlighet. Eftersom hög benzimidazolkoncentration motverkade segmentrörligheten genom bildandet av starka vätebindningar var benzimidazolkoncentrationen tvungen att balanseras så att en rimligt hög segementrörlighet kunde bibehållas. Resultaten visade att man är tvungen att tillverka polymerer med hög koncentration av den protonledande komponenten och med hög segmentrörlighet för att uppnå hög protonledning. Detta skulle kunna åstadkommas genom att använda längre sidokedjor när benzimidazolen ympas på polymeren. (Less)
Abstract
Proton transport is a fundamental process that can be found in many systems in nature, as well as in technical devices, such as fuel cells, electrochromic devices and various types of sensors. Fuel cell technology is considered as environmentally friendly because fuel cells are not limited by the Carnot cycle, and efficiently converts chemical energy into electrical energy which can be used for powering cars, laptops, buildings etc. One of the most promising fuel cell for portable devices is the polymer electrolyte membrane fuel cell (PEMFC). However, commercialization of PEMFC's is limited by several factors, including the insufficient properties of the current polymer membrane at temperatures above 100 º C, which are basically a... (More)
Proton transport is a fundamental process that can be found in many systems in nature, as well as in technical devices, such as fuel cells, electrochromic devices and various types of sensors. Fuel cell technology is considered as environmentally friendly because fuel cells are not limited by the Carnot cycle, and efficiently converts chemical energy into electrical energy which can be used for powering cars, laptops, buildings etc. One of the most promising fuel cell for portable devices is the polymer electrolyte membrane fuel cell (PEMFC). However, commercialization of PEMFC's is limited by several factors, including the insufficient properties of the current polymer membrane at temperatures above 100 º C, which are basically a consequence of the water that is necessary in the polymer membrane to facilitate the proton conduction. By operating the cell at temperatures in the range 150-200 ºC, many advantages could be reached at a system level.



Consequently, the concept of fully polymeric proton conductors was investigated where the proton carriers were tethered to polymer backbones in order to avoid any leakage of the proton carrying component at elevated temperatures. Benzimidazole was chosen as the proton carrying component due to its inherent proton conducting properties and its high chemical and thermal stability. A series of model materials consisting of polymers with different chain structures and architectures and having benzimidazole units tethered via side chains were synthesized and investigated as proton conductors. A modular scheme to conveniently incorporate benzimidazole via thiol-ene coupling was developed. In general, the glass transition temperature was drastically increased when benzimidazole were tethered to the polymers with short side chains, indicating suppression of the segmental mobility of the polymers. This effect was attributed to the formation of hydrogen bonds between the benzimidazole units. When the length of the side chains was increased, the benzimidazole seemed to become decoupled from the polymer mobility of the backbone. It was concluded that the benzimidazole concentration and the segmental mobility of the polymers were the most important parameters to obtain high proton conductivities regardless of the polymer architecture. The conductivity was facilitated by high benzimidazole concentrations and high segmental mobility. However, since high benzimidazole concentrations suppressed the segmental mobility by the formation of strong hydrogen bonds, the benzimidazole content had to be balanced so that a reasonably high segmental mobility was retained. These findings suggested that polymers with a high concentration of the proton carrying species and a high segmental mobility have to be prepared in order to reach high conductivities. This may be accomplished by using long side chains when tethering the benzimidazole. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Tenhu, Heikki, Laboratory of Polymer Chemistry, University of Helsinki, Finland
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Polymerteknik, biopolymers, Kemiteknik och kemisk teknologi, Polymer technology, Chemical technology and engineering, Materiallära, materialteknik, Material technology, Makromolekylär kemi, Macromolecular chemistry, proton-exchange membrane fuel cell, structure diffusion, thiol-ene reaction, segmental mobility, high temperature, benzimidazole, block copolymers, polymer electrolyte, anhydrous proton conductivity
pages
127 pages
publisher
KFS AB
defense location
Room K:C, Centre for Chemistry and Chemical Engineering,Getingevägen 60, Lund Institute of Technology
defense date
2005-12-13 10:30
ISBN
91-7422-099-3
language
English
LU publication?
yes
id
bcad040d-55d6-44b6-8258-fabc5f46b905 (old id 545838)
date added to LUP
2007-10-13 12:58:31
date last changed
2016-09-19 08:45:02
@misc{bcad040d-55d6-44b6-8258-fabc5f46b905,
  abstract     = {Proton transport is a fundamental process that can be found in many systems in nature, as well as in technical devices, such as fuel cells, electrochromic devices and various types of sensors. Fuel cell technology is considered as environmentally friendly because fuel cells are not limited by the Carnot cycle, and efficiently converts chemical energy into electrical energy which can be used for powering cars, laptops, buildings etc. One of the most promising fuel cell for portable devices is the polymer electrolyte membrane fuel cell (PEMFC). However, commercialization of PEMFC's is limited by several factors, including the insufficient properties of the current polymer membrane at temperatures above 100 º C, which are basically a consequence of the water that is necessary in the polymer membrane to facilitate the proton conduction. By operating the cell at temperatures in the range 150-200 ºC, many advantages could be reached at a system level.<br/><br>
<br/><br>
Consequently, the concept of fully polymeric proton conductors was investigated where the proton carriers were tethered to polymer backbones in order to avoid any leakage of the proton carrying component at elevated temperatures. Benzimidazole was chosen as the proton carrying component due to its inherent proton conducting properties and its high chemical and thermal stability. A series of model materials consisting of polymers with different chain structures and architectures and having benzimidazole units tethered via side chains were synthesized and investigated as proton conductors. A modular scheme to conveniently incorporate benzimidazole via thiol-ene coupling was developed. In general, the glass transition temperature was drastically increased when benzimidazole were tethered to the polymers with short side chains, indicating suppression of the segmental mobility of the polymers. This effect was attributed to the formation of hydrogen bonds between the benzimidazole units. When the length of the side chains was increased, the benzimidazole seemed to become decoupled from the polymer mobility of the backbone. It was concluded that the benzimidazole concentration and the segmental mobility of the polymers were the most important parameters to obtain high proton conductivities regardless of the polymer architecture. The conductivity was facilitated by high benzimidazole concentrations and high segmental mobility. However, since high benzimidazole concentrations suppressed the segmental mobility by the formation of strong hydrogen bonds, the benzimidazole content had to be balanced so that a reasonably high segmental mobility was retained. These findings suggested that polymers with a high concentration of the proton carrying species and a high segmental mobility have to be prepared in order to reach high conductivities. This may be accomplished by using long side chains when tethering the benzimidazole.},
  author       = {Persson, Christian},
  isbn         = {91-7422-099-3},
  keyword      = {Polymerteknik,biopolymers,Kemiteknik och kemisk teknologi,Polymer technology,Chemical technology and engineering,Materiallära,materialteknik,Material technology,Makromolekylär kemi,Macromolecular chemistry,proton-exchange membrane fuel cell,structure diffusion,thiol-ene reaction,segmental mobility,high temperature,benzimidazole,block copolymers,polymer electrolyte,anhydrous proton conductivity},
  language     = {eng},
  pages        = {127},
  publisher    = {ARRAY(0x8677530)},
  title        = {Intrinsically Proton-Conducting Benzimidazole Units Tethered to Different Polymer Chain Architectures},
  year         = {2005},
}