Hydroxide Degradation Pathways for Substituted Trimethylammonium Cations: A DFT Study
Substituted trimethylammonium cations serve as small molecule analogues for tetherable cations in anion exchange membranes. In turn, these membranes serve as the basis for alkaline membrane fuel cells by allowing facile conduction of hydroxide. As these cations are susceptible to hydroxide attack, they degrade over time and greatly limit the lifetime of the fuel cell. In this research, we performed density functional theory calculations to investigate the degradation pathways of substituted trimethylammonium cations to probe the relative durability of cation tethering strategies in alkyl and aromatic tethers. Our results show that significant changes in calculated energy barriers occur when substitution groups change. Specifically, we have found that, when available, the Hofmann elimination pathway is the most vulnerable pathway for degradation; however, this barrier is also found to depend on the carbon chain length and number of hydrogens susceptible to Hofmann elimination. S{sub N}2 barriers were also investigated for both methyl groups and substitution groups. The reported findings give important insight into potential tethering strategies for trimethylammonium cations in anion exchange membranes.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22), Division of Materials Science and Engineering
- DOE Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1047946
- Report Number(s):
- NREL/JA-2C00-55329; TRN: US201216%%575
- Journal Information:
- Journal of Physical Chemistry. C, Vol. 116, Issue 17; ISSN 1932-7447
- Country of Publication:
- United States
- Language:
- English
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