Uncovering Alternate Pathways to Nafion Membrane Degradation in Fuel Cells with First-Principles Modeling
Name
Uncovering_Alternate_Pathways_to_Nafion_Membrane_Degradation_in_Fuel_Cells_with_First-Principles_Modeling_v1.pdf
Description
Submitted version
Size
3.27 MB
Format
Adobe PDF
Checksum (MD5)
ed889be1d089abae1fcc92b83f26c1df
Author(s)
Bajaj, Akash
Liu, Fang
Kulik, Heather J
Date Issued
2020
Journal
Journal of Physical Chemistry C
Publisher
American Chemical Society (ACS)
Version
Original manuscript
Abstract
Polymer electrolyte membrane fuel cells (PEMFCs) represent promising energy storage solutions, but challenges remain to maximize their utility. Nafion is frequently employed as the PEMFC membrane material, but degradation of Nafion can limit the life of PEMFCs. Using hybrid density functional theory (DFT), we carry out reaction pathway analysis on a range of candidate degradation pathways on both pristine and defect-containing models of Nafion. Degradation of pristine Nafion initiated by hydrogen radicals involves moderate (ca. 20 kcal/mol) barriers lower than alternative pathways initiated by hydroxyl radicals. We propose a new pathway for continued Nafion degradation after initial H radical attack in the presence of H2O2. This pathway has a modest barrier and provides a mechanistic basis for the production of experimentally observed trifluoroacetic acid and hydrogen fluoride. Our work suggests inherent limits to mechanistic studies that use hydroxyl radical as the sole radical source to model Nafion degradation under operating conditions. We observe that hydroxyl-radical-only degradation mechanisms have barriers competitive with hydrogen radical species only for initiation at carboxylic acid defects on the main chain or sulfonic acid functional groups on the Nafion side chain. We confirm our observations with DFT by comparison to correlated wave function theory. Our study highlights the importance of thorough first-principles modeling to identify the most probable, low-energy pathways for materials degradation.
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
Massachusetts Institute of Technology. Department of Materials Science and Engineering
Terms of Use
Creative Commons Attribution-Noncommercial-Share Alike
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1021/ACS.JPCC.0C04417
