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Lookup NU author(s): Sam Power, Dr Corinne Wills, Dr Casey Dixon, Dr Paul Waddell, Dr Julian Knight, Professor Mohamed MamloukORCiD, Dr Simon DohertyORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
Understanding the alkaline stability of quaternary ammonium (QA) cations tethered to polymer-based anion exchange membranes (AEMs) is crucial to advance the long-term performance of AEM based devices such as fuel cells and electrolysers. A library of model QA cations with N-phenyl and N-benzyl tethers have been synthesised and alkaline degradation revealed that the former were much less stable towards hydroxide than their benzylic counterparts. DFT studies conducted at different levels of hydration support the relative stability of the QA cations and demonstrate the critical effect of hydroxide solvation on their alkaline stability. Calculations show that reducing the hydration number of -OH increases the rate of degradation and leads to a change in the major degradation pathway. The N-benzyl-6-azonia-spiro[5.5]undecane (N-benzyl-ASU) cation was found to be the most stable QA group under standard testing conditions with a half-life of 2,595 h in 3M NaOH at a hydration number of 4.8, despite N-phenyl-ASU having a higher computed LUMO energy which suggests that the LUMO energy alone is not an accurate indicator of alkaline stability. This study highlights the importance of considering the method of tethering the QA group to the polymer backbone and controlling the level of hydroxide hydration when synthesising and testing QA cations for use as AEMs. This work has led to structure-stability correlations that will inform the design of QA cations with improved stability profiles.
Author(s): Power SDT, Wills C, Dixon CM, Waddell P, Knight J, Mamlouk M, Doherty S
Publication type: Article
Publication status: Published
Journal: ACS Applied Energy Materials
Year: 2025
Pages: ePub ahead of Print
Online publication date: 28/06/2025
Acceptance date: 20/06/2025
Date deposited: 29/06/2025
ISSN (electronic): 2574-0962
Publisher: American Chemical Society
URL: https://doi.org/10.1021/acsaem.5c01293
DOI: 10.1021/acsaem.5c01293
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