Pore-Water and Proton Transport in Polymer Electrolyte Membrane Fuel Cell: Molecular Dynamics and Mono- and Bimodal Wetting Treatments of Mesopore Hydrated Nafion.
dc.contributor.author | Hwang, Gi Suk | en_US |
dc.date.accessioned | 2011-01-18T16:12:38Z | |
dc.date.available | NO_RESTRICTION | en_US |
dc.date.available | 2011-01-18T16:12:38Z | |
dc.date.issued | 2010 | en_US |
dc.date.submitted | 2010 | en_US |
dc.identifier.uri | https://hdl.handle.net/2027.42/78840 | |
dc.description.abstract | Water states and water/proton transport in nanopores of hydrated Nafion, a chosen electrolyte in polymer electrolyte membrane fuel cell, are explained using molecular dynamics (MD) aided bimodal pore-size/water-wetting model. The bimodal model is developed based on the effective Debye screening length for pore water confined by heterogeneously ionized surface, and using small-angle X-ray scattering (SAXS) measurements and existing pore-size distribution. The smaller pores (1 nm) critically confine water and promote capillary condensation (hydrophilic-like), while hindering transport. The larger pores (4 nm) delay the condensation (hydrophobic-like), while allowing bulk-like transport. In a pore network, the small pores selectively wet, while the large pores provide dominant adsorption and transport channels, a novel attribute of the bimodal model. Also, in contrast to the existing Nafion backbone-hydration model, a hydration-dependent, temperature-dependent sulfonic acid surface density is proposed. The bimodal model succeeds in predicting the pore-water states and the transition in adsorption with capillary condensation in the large pores and negligible contribution from the small pores. These are in agreement with experiments. This transition also results in the proton conductivity jump by allowing dominant proton hopping through the larger pores in the network. The bimodal wetting describes the capillary water flow, where the small hydrophilic-like pores provide dominant flow channels, whereas water in the large pores remains immobile due to adsorption only. This water flow network results in lower liquid saturation distribution, in general agreement with the limited experimental results. At elevated temperatures, it is suggested that the sulfonic acid surface site density reduces due to pore surface stretching (relaxing backbone), resulting in hydrophobicity, most pronounced in the large pores. This delays the capillary condensation and decreases adsorption, and masks the transition in proton conductivity. The pore-water state/content for optimal cell operation is also discussed. | en_US |
dc.format.extent | 6180204 bytes | |
dc.format.extent | 1373 bytes | |
dc.format.mimetype | application/pdf | |
dc.format.mimetype | text/plain | |
dc.language.iso | en_US | en_US |
dc.subject | Pore Water | en_US |
dc.subject | Molecular Dynamics | en_US |
dc.subject | Adsorption | en_US |
dc.subject | Proton Transport | en_US |
dc.subject | Nafion | en_US |
dc.subject | Water Diffusion | en_US |
dc.title | Pore-Water and Proton Transport in Polymer Electrolyte Membrane Fuel Cell: Molecular Dynamics and Mono- and Bimodal Wetting Treatments of Mesopore Hydrated Nafion. | en_US |
dc.type | Thesis | en_US |
dc.description.thesisdegreename | PhD | en_US |
dc.description.thesisdegreediscipline | Mechanical Engineering | en_US |
dc.description.thesisdegreegrantor | University of Michigan, Horace H. Rackham School of Graduate Studies | en_US |
dc.contributor.committeemember | Kaviany, Massoud | en_US |
dc.contributor.committeemember | Lastoskie, Christian M. | en_US |
dc.contributor.committeemember | Matzger, Adam J. | en_US |
dc.contributor.committeemember | Thompson Jr, Levi T. | en_US |
dc.subject.hlbsecondlevel | Mechanical Engineering | en_US |
dc.subject.hlbtoplevel | Engineering | en_US |
dc.description.bitstreamurl | http://deepblue.lib.umich.edu/bitstream/2027.42/78840/1/gshwang_1.pdf | |
dc.owningcollname | Dissertations and Theses (Ph.D. and Master's) |
Files in this item
Remediation of Harmful Language
The University of Michigan Library aims to describe library materials in a way that respects the people and communities who create, use, and are represented in our collections. Report harmful or offensive language in catalog records, finding aids, or elsewhere in our collections anonymously through our metadata feedback form. More information at Remediation of Harmful Language.
Accessibility
If you are unable to use this file in its current format, please select the Contact Us link and we can modify it to make it more accessible to you.