Virginia Tech
Structure-Morphology-Property Relationships in Perfluorosulfonic Acid Ionomer Dispersions, Membranes, and Thin Films to Advance Hydrogen Fuel Cell Applications
Abstract
dc:description.abstractRecent efforts toward the commercialization of hydrogen fuel cells, a sustainable energy technology, have led to interest in the effects of industrial processing parameters on the morphology and properties of fuel cell ionomers. The ionomer functions as a solid electrolyte membrane on the order of microns thick and as a thin film on the order of tens of nanometers in the catalyst layer. Industrial manufacture of the membrane and catalyst layer is typically a roll-to-roll process that involves casting a colloidal dispersion of the fuel cell ionomer in predominantly mixed alcohol/water solvent systems onto a backing film or substrate, followed by evaporation of the solvent and annealing of the ionomer at elevated temperatures. The current benchmark fuel cell ionomers are a class of polymers with pendant perfluorinated side chains terminating in sulfonic acid groups, called perflurosulfonic acid ionomers (PFSAs). The purpose of this dissertation is to investigate the effects of industrial processing parameters such as dispersion solvent composition, solvent evaporation temperature, and annealing temperature on fuel cell-relevant properties of PFSA solid electrolyte membranes and model thin films. Particular focus is given to newer-generation PFSAs and the effect of their different chemical structures on the morphology and properties of dispersions, membranes, and thin films. Dipole-dipole interactions between colloidal aggregates modulated by solvent composition were found to significantly influence the viscosity of PFSA dispersions. A framework of PFSA-solvent interactions is developed to predict the onset of dipole-dipole interactions as a function of PFSA chemical structure and solvent composition. Increased steric hindrance of shorter PFSA side chain chemical structures is found to inhibit morphological development, resulting in membranes with poorer wet and dry mechanical properties. A shorter side-chain PFSA is suggested to require higher processing temperatures to achieve performance equivalent to a PFSA with slightly longer side chain. The morphology and properties of model PFSA thin films are demonstrated to decay to quasi-equilibrium values upon physical aging at both low and high relative humidity (RH). Thin film swelling curves are demonstrated to be superposable by implementing an aging time-RH shift factor, allowing for prediction of quasi-equilibration times under given fuel cell operating conditions.
Degree
thesis:*- Name thesis:degree_name
- Doctor of Philosophy
- Level thesis:degree_level
- doctoral
- Discipline thesis:degree_discipline
- Macromolecular Science and Engineering
- Department dc:contributor.department
- Chemistry
- Grantor dc:publisher
- Virginia Tech
- Year dc:date.issued
- 2022
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Novy, Melissa Hoang Lan
- Chair dc:contributor.committeechair
-
- Moore, Robert Bowen
- Committee members dc:contributor.committeemember
-
- Bortner, Michael J.
- Kusoglu, Ahmet
- Ellis, Michael W.
- Lin, Feng
Subjects
dc:subject × 4Rights
dc:rights- Statement dc:rights
-
- In Copyright
- Licence dc:rights.uri
- Language dc:language.iso
- en
Identifiers
dc:identifier.*- Dc Identifier Other
- vt_gsexam:35066
- OAI identifier oai:identifier
- oai:vtechworks.lib.vt.edu:10919/110879