Advanced

Proton-Conducting Sulfonated and Phosphonated Polymers and Fuel Cell Membranes by Chemical Modification of Polysulfones

Lafitte, Benoit LU (2007)
Abstract (Swedish)
Popular Abstract in Swedish

Polymerelektrolytbränslecellen utmärker sig som en framtida effektiv och miljövänlig kraftkälla för bland annat fordon. Den bakomliggande teknologin är dock komplex och grundar sig till stor del på material och komponenter som kräver ytterliggare utveckling. En av de största hindren för bränslecellsteknologins utveckling är kravet på nya, långlivade och billiga polymermembran som tillåter bränslecellen att fungera vid höga temperaturer utan krav på omfattande uppfuktning. Utvecklingen av protonledande membran med en sådan egenskapsprofil utgör idag en verklig utmaning för polymer- och materialkemister världen över. I detta sammanhang riktas stora satsningar mot ett antal olika kemiskt stabila... (More)
Popular Abstract in Swedish

Polymerelektrolytbränslecellen utmärker sig som en framtida effektiv och miljövänlig kraftkälla för bland annat fordon. Den bakomliggande teknologin är dock komplex och grundar sig till stor del på material och komponenter som kräver ytterliggare utveckling. En av de största hindren för bränslecellsteknologins utveckling är kravet på nya, långlivade och billiga polymermembran som tillåter bränslecellen att fungera vid höga temperaturer utan krav på omfattande uppfuktning. Utvecklingen av protonledande membran med en sådan egenskapsprofil utgör idag en verklig utmaning för polymer- och materialkemister världen över. I detta sammanhang riktas stora satsningar mot ett antal olika kemiskt stabila jon-innehållande aromatiska polymerer. Inom ramen för detta doktorandprojekt har nya bränslecellsmembran baserade på aromatiska polysulfoner med funktionella sulfon- eller fosfongrupper designats, syntetiserats och undersökts. Polysulfoner är högpresterande termoplaster med utmärkta kemiska, mekaniska och termiska egenskaper. Genom att isolera de joniska sätena på polymerens sidokedjor ? långt från dess huvudkedja ? kan den nanometriska fasseparationen mellan de hydrofoba och hydrofila domänerna i membranen manipuleras. Detta kan i sin tur ge upphov till membran med goda egenskaper, framför allt en välbalanserad vattenupptagningsförmåga.



Membran med en kontrollerad vattenupptagningsförmåga framställdes genom att fästa sulfonsyraenheter på molekylärt styva aromatiska sidokedjor. Detta kunde åstadkommas genom att reagera litierad PSU med 2-sulfobensoesyraanhydrid. Längden på de aromatiska sidokedjorna kunde ökas genom utvecklandet av en ny reaktionsväg där litierade polysulfoner fick reagera med 4-fluorobensoylklorid. Detta gav upphov till polymerer med fluorobensoyl-sidokedjor. Fluoratomerna i dessa kedjor var aktiverade för nukleofil substitution, vilket innebar att en mängd olika nukleofiler kunde användas för att vidare modifiera polymeren. I ett första experimentellt försök byttes de aktiverade fluoridgrupperna ut mot sulfofenoxi- eller sulfonaftoxienheter i en nukleofil substitution, katalyserad av kaliumkarbonat. Denna reaktion gick till full omsättning och substitutionsgraden kunde enkelt kontrolleras genom litieringsgraden av polymeren i det första steget. Genom att använda en snarlik metodik kunde polymerer med di- och trisulfonerade aromatiska sidokedjor syntetiseras. I synnerhet membran baserade på en polysulfonhuvudkedja med sidokedjor av disulfonerad naftoxibenzoyl påvisade en tydlig fasseparation mellan de hydrofoba huvudkedjorna och de hydrofila sulfonerade sidokejorna, och kunde därmed bilda ett väldefinerat nätverk av vattenfyllda nanoporer. Detta nätverk gav upphov till en utmärkt protonledning och en välkontrollerad vattenupptagning, i motsats till konventionellt sulfonerade aromatiska polymerer.



Det var också av stort intresse att undersöka alternativa syraenheter då desulfonering kan vara en kritisk faktor vid höga temperaturer. Jonomerer baserade på fosfonsyraenheter har normalt en högre hydrotermisk stabilitet jämfört med sulfonsyraenheter, och är därför intressanta i detta sammanhang. En fosfonerad polysulfon framställdes genom att reagera litierad polysulfon med klorofosfonsyraestrar. Koncentrationen av dessa fosfonsyraenheter, som fästes direkt på de aromatiska ringarna i polysulfonen, var dock för låg för att ge upphov till ett tillräcklig vattenupptag och protonledning. Detta problem kunde kringgås på ett originellt sätt genom att först syntetisera en polymer med joderade bensoylsidokedjor med hjälp av litieringskemi. Polysulfonen modifierades sedan ytterliggare med syfte att koppla sura -CF2PO3H2 grupper på de aromatiska sidokedjorna. Membran framställda från polymerer med 0.90 mmol fosfonsyraenheter per gram torr polymer tog upp 6 vikts-% vatten efter att ha sänkts ned i vatten vid rumstemperatur. Ledningsförmågan hos detta membran visade sig dessutom vara jämförbar med membran baserade på en sulfonerad polysulfon med 0.86 mmol sulfonsyra per gram torr polymer. (Less)
Abstract
The proton exchange membrane fuel cell (PEMFC) is currently emerging as an efficient and environmentally friendly power source. The technology is very complex and relies ultimately on materials and components which need further development. One of the major hurdles for advancing the PEMFC technology is currently the demand for new durable low-cost polymeric membranes that will allow fuel cell operation at high temperatures without extensive humidification requirements. Thus, the design and preparation of functional high-performance proton-conducting membranes with the critical set of properties is a major challenge for polymer and materials chemists around the world today. In this context, major efforts are directed towards different... (More)
The proton exchange membrane fuel cell (PEMFC) is currently emerging as an efficient and environmentally friendly power source. The technology is very complex and relies ultimately on materials and components which need further development. One of the major hurdles for advancing the PEMFC technology is currently the demand for new durable low-cost polymeric membranes that will allow fuel cell operation at high temperatures without extensive humidification requirements. Thus, the design and preparation of functional high-performance proton-conducting membranes with the critical set of properties is a major challenge for polymer and materials chemists around the world today. In this context, major efforts are directed towards different durable aromatic main-chain ionomers. In the present thesis project, new fuel cell membrane materials based on polysulfones (PSUs) functionalized with sulfonated or phosphonated moieties via lithiation chemistry have been designed, synthesized and investigated. PSUs are high performance thermoplastics with excellent chemical, mechanical and thermal properties. By isolating the ionic sites on side chains, away from the polymer main chain, the nanophase separation between the hydrophobic and the hydrophilic domains of the hydrated membrane may be manipulated and influenced, which in turn may provide membranes with balanced water sorption characteristics.



Membranes with controlled water uptake were obtained by attaching the sulfonic acid unit to stiff aromatic side chains. This was conveniently achieved by reacting lithiated PSU with 2-sulfobenzoic acid cyclic anhydride in a one-pot reaction. In order to increase the length of the aromatic spacers, a new pathway was developed where lithiated PSU was reacted with 4-fluorobenzoyl chloride. This afforded PSUs with pendant fluorobenzoyl side chains in which the fluoride groups are activated for nucleophilic substitution. As a result, a wide range of nucleophiles may be used to further substitute the polymer. In an initial effort, the activated fluoride groups were replaced by sulfophenoxy or sulfonaphthoxy units in a potassium carbonate-mediated nucleophilic substitution reaction. This reaction proceeded under full conversion and the degree of substitution was easily controlled by the degree of lithiation in the first step. Using a similar methodology, PSUs carrying di- and trisulfonated aromatic side chains were successfully synthesized. In particular, membranes based on a PSU main chain carrying disulfonated napthoxybenzoyl side chains exhibited a distinct phase separation between the hydrophobic polymer main chain and the hydrophilic sulfonated side chains, and formed a well-defined and efficient network of water-filled nanopores. The latter resulted in excellent proton conductivity at controlled levels of water uptake in contrast to conventional sulfonated aromatic polymers.



The investigation of alternative acidic moieties is also of great interest since desulfonation may become a critical issue at high temperatures. This has motivated the search for ionomers based on phosphonic acid units, which generally have a higher hydrothermal stability than sulfonic acid units. Phosphonated PSU was successfully prepared by reacting lithiated PSU with chlorophosphonic acid esters. However, as underlined in a recent literature review, the acidity of phosphonic acid units directly attached to aromatic rings was too low to result in reasonable levels of water uptake. An original approach was therefore developed in which PSU with pendant iodinated benzoyl side chains were prepared via lithiation chemistry. The latter polymer was then further modified to yield the more acidic ?CF2PO3H2 units located on aromatic side chains. Membranes based on ionomers having 0.90 mmol of phosphonic acid units/g of dry polymer took up 6 wt% water when immersed at room temperature, and levels of conductivity comparable to those reached by a membrane based on a sulfonated polysulfone having 0.86 mmol of sulfonic acid/g of dry polymer were recorded. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Dr. Améduri, Bruno, Laboratory of Macromolecular Chemistry, UMR (CNRS) 5076, Ecole Nat Sup de Chimie de Montpellier, Fra
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Macromolecular chemistry, Makromolekylär kemi, Material technology, Materiallära, materialteknik, chemical modification, lithiation, fuel cells, polyelectrolyte, sulfonated polymers, proton-conducting polymer membranes polysulfone, phosphonated polymers
pages
207 pages
publisher
Division of Polymer & Materials Chemistry
defense location
Center for Chemistry and Chemical Engineering, Lecture Hall B
defense date
2007-02-26 10:15
ISBN
978-91-7422-146-6
language
English
LU publication?
yes
id
27b6932f-81a9-4e6c-9579-80bbce1c0473 (old id 548017)
date added to LUP
2007-10-09 11:49:36
date last changed
2016-09-19 08:45:15
@misc{27b6932f-81a9-4e6c-9579-80bbce1c0473,
  abstract     = {The proton exchange membrane fuel cell (PEMFC) is currently emerging as an efficient and environmentally friendly power source. The technology is very complex and relies ultimately on materials and components which need further development. One of the major hurdles for advancing the PEMFC technology is currently the demand for new durable low-cost polymeric membranes that will allow fuel cell operation at high temperatures without extensive humidification requirements. Thus, the design and preparation of functional high-performance proton-conducting membranes with the critical set of properties is a major challenge for polymer and materials chemists around the world today. In this context, major efforts are directed towards different durable aromatic main-chain ionomers. In the present thesis project, new fuel cell membrane materials based on polysulfones (PSUs) functionalized with sulfonated or phosphonated moieties via lithiation chemistry have been designed, synthesized and investigated. PSUs are high performance thermoplastics with excellent chemical, mechanical and thermal properties. By isolating the ionic sites on side chains, away from the polymer main chain, the nanophase separation between the hydrophobic and the hydrophilic domains of the hydrated membrane may be manipulated and influenced, which in turn may provide membranes with balanced water sorption characteristics.<br/><br>
<br/><br>
Membranes with controlled water uptake were obtained by attaching the sulfonic acid unit to stiff aromatic side chains. This was conveniently achieved by reacting lithiated PSU with 2-sulfobenzoic acid cyclic anhydride in a one-pot reaction. In order to increase the length of the aromatic spacers, a new pathway was developed where lithiated PSU was reacted with 4-fluorobenzoyl chloride. This afforded PSUs with pendant fluorobenzoyl side chains in which the fluoride groups are activated for nucleophilic substitution. As a result, a wide range of nucleophiles may be used to further substitute the polymer. In an initial effort, the activated fluoride groups were replaced by sulfophenoxy or sulfonaphthoxy units in a potassium carbonate-mediated nucleophilic substitution reaction. This reaction proceeded under full conversion and the degree of substitution was easily controlled by the degree of lithiation in the first step. Using a similar methodology, PSUs carrying di- and trisulfonated aromatic side chains were successfully synthesized. In particular, membranes based on a PSU main chain carrying disulfonated napthoxybenzoyl side chains exhibited a distinct phase separation between the hydrophobic polymer main chain and the hydrophilic sulfonated side chains, and formed a well-defined and efficient network of water-filled nanopores. The latter resulted in excellent proton conductivity at controlled levels of water uptake in contrast to conventional sulfonated aromatic polymers.<br/><br>
<br/><br>
The investigation of alternative acidic moieties is also of great interest since desulfonation may become a critical issue at high temperatures. This has motivated the search for ionomers based on phosphonic acid units, which generally have a higher hydrothermal stability than sulfonic acid units. Phosphonated PSU was successfully prepared by reacting lithiated PSU with chlorophosphonic acid esters. However, as underlined in a recent literature review, the acidity of phosphonic acid units directly attached to aromatic rings was too low to result in reasonable levels of water uptake. An original approach was therefore developed in which PSU with pendant iodinated benzoyl side chains were prepared via lithiation chemistry. The latter polymer was then further modified to yield the more acidic ?CF2PO3H2 units located on aromatic side chains. Membranes based on ionomers having 0.90 mmol of phosphonic acid units/g of dry polymer took up 6 wt% water when immersed at room temperature, and levels of conductivity comparable to those reached by a membrane based on a sulfonated polysulfone having 0.86 mmol of sulfonic acid/g of dry polymer were recorded.},
  author       = {Lafitte, Benoit},
  isbn         = {978-91-7422-146-6},
  keyword      = {Macromolecular chemistry,Makromolekylär kemi,Material technology,Materiallära,materialteknik,chemical modification,lithiation,fuel cells,polyelectrolyte,sulfonated polymers,proton-conducting polymer membranes polysulfone,phosphonated polymers},
  language     = {eng},
  pages        = {207},
  publisher    = {ARRAY(0x968a080)},
  title        = {Proton-Conducting Sulfonated and Phosphonated Polymers and Fuel Cell Membranes by Chemical Modification of Polysulfones},
  year         = {2007},
}