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A comparative study of anion-exchange membranes tethered with different hetero-cycloaliphatic quaternary ammonium hydroxides

Dang, Hai-Son LU and Jannasch, Patric LU (2017) In Journal of Materials Chemistry A 5(41). p.21965-21978
Abstract
Quaternary ammonium (QA) cations with high alkaline stability are crucial for the long term performance of anion-exchange membrane (AEM) fuel cells. Here, we have tethered poly(phenylene oxide) (PPO) with 8 different hetero-cycloaliphatic QA cations via pentyl spacer chains. The thermal and alkaline stability, as well as hydroxide ion conductivity, were systematically evaluated with the primary aim to identify degradation reactions and establish cation design principles. The study included AEMs functionalized with 1-methylazepanium, 1-methylpyrrolidinium, 1-methylmorpholinium, quinuclidinium, as well as 1-methyl-, 1,4-dimethyl-, 1,3,5-trimethyl-, and 1,2,6-trimethylpiperidinium, all within a narrow ion exchange capacity (IEC) range. For... (More)
Quaternary ammonium (QA) cations with high alkaline stability are crucial for the long term performance of anion-exchange membrane (AEM) fuel cells. Here, we have tethered poly(phenylene oxide) (PPO) with 8 different hetero-cycloaliphatic QA cations via pentyl spacer chains. The thermal and alkaline stability, as well as hydroxide ion conductivity, were systematically evaluated with the primary aim to identify degradation reactions and establish cation design principles. The study included AEMs functionalized with 1-methylazepanium, 1-methylpyrrolidinium, 1-methylmorpholinium, quinuclidinium, as well as 1-methyl-, 1,4-dimethyl-, 1,3,5-trimethyl-, and 1,2,6-trimethylpiperidinium, all within a narrow ion exchange capacity (IEC) range. For reference, PPO was also functionalized with trimethylammonium and dipropylmethylammonium cations on pentyl spacers, and with trimethylammonium and 1-methylpiperidinium QAs in benzylic positions directly on the PPO backbone. The alkaline stability of hetero-cycloaliphatic QA cations was found to depend critically on their position in the polymer structure, ring size, the presence of an additional heteroatom and ring substitution pattern. For example, 1,2,6-trimethylpiperidinium and 1-methylazepanium degraded via Hofmann elimination and 1-methylmorpholinium via ring opening by both Hofmann elimination and substitution reactions, while no degradation was detected by 1H NMR spectroscopy of other cations after 16 days in 1 M NaOH at 90 °C. The hydroxide ion conductivity of the AEMs in the study reached between 64 and 150 mS cm-1 at 80 °C, depending on cation and IEC. AEMs tethered with pyrrolidinium, piperidinium and quinuclidinium cations via pentyl spacers were found to show the best overall properties. Hence, the combined results provide insights that may guide the selection of cationic groups and membrane materials to improve the durability and performance of alkaline electrochemical energy conversion and storage devices. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Materials Chemistry A
volume
5
issue
41
pages
21965 - 21978
publisher
Royal Society of Chemistry
external identifiers
  • scopus:85032358464
  • wos:000413734800040
ISSN
2050-7488
DOI
10.1039/C7TA06029G
language
English
LU publication?
yes
id
77916201-8e0e-470f-928c-7cb0a7cda0fe
date added to LUP
2017-10-02 19:53:23
date last changed
2018-01-16 13:20:20
@article{77916201-8e0e-470f-928c-7cb0a7cda0fe,
  abstract     = {Quaternary ammonium (QA) cations with high alkaline stability are crucial for the long term performance of anion-exchange membrane (AEM) fuel cells. Here, we have tethered poly(phenylene oxide) (PPO) with 8 different hetero-cycloaliphatic QA cations via pentyl spacer chains. The thermal and alkaline stability, as well as hydroxide ion conductivity, were systematically evaluated with the primary aim to identify degradation reactions and establish cation design principles. The study included AEMs functionalized with 1-methylazepanium, 1-methylpyrrolidinium, 1-methylmorpholinium, quinuclidinium, as well as 1-methyl-, 1,4-dimethyl-, 1,3,5-trimethyl-, and 1,2,6-trimethylpiperidinium, all within a narrow ion exchange capacity (IEC) range. For reference, PPO was also functionalized with trimethylammonium and dipropylmethylammonium cations on pentyl spacers, and with trimethylammonium and 1-methylpiperidinium QAs in benzylic positions directly on the PPO backbone. The alkaline stability of hetero-cycloaliphatic QA cations was found to depend critically on their position in the polymer structure, ring size, the presence of an additional heteroatom and ring substitution pattern. For example, 1,2,6-trimethylpiperidinium and 1-methylazepanium degraded via Hofmann elimination and 1-methylmorpholinium via ring opening by both Hofmann elimination and substitution reactions, while no degradation was detected by <sup>1</sup>H NMR spectroscopy of other cations after 16 days in 1 M NaOH at 90 °C. The hydroxide ion conductivity of the AEMs in the study reached between 64 and 150 mS cm<sup>-1</sup> at 80 °C, depending on cation and IEC. AEMs tethered with pyrrolidinium, piperidinium and quinuclidinium cations via pentyl spacers were found to show the best overall properties. Hence, the combined results provide insights that may guide the selection of cationic groups and membrane materials to improve the durability and performance of alkaline electrochemical energy conversion and storage devices.},
  author       = {Dang, Hai-Son and Jannasch, Patric},
  issn         = {2050-7488},
  language     = {eng},
  number       = {41},
  pages        = {21965--21978},
  publisher    = {Royal Society of Chemistry},
  series       = {Journal of Materials Chemistry A},
  title        = {A comparative study of anion-exchange membranes tethered with different hetero-cycloaliphatic quaternary ammonium hydroxides},
  url          = {http://dx.doi.org/10.1039/C7TA06029G},
  volume       = {5},
  year         = {2017},
}