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Type of Document Dissertation Author Hall, Timothy David URN etd-09042007-154131 Title Performance Enhancement of Low Temperature Polymer Electrolyte Membrane Fuel Cells by Catalyst and Support Layer Modifications Degree Doctor of Philosophy Department Chemical Engineering Advisory Committee
Advisor Name Title George S. Howard Committee Chair Albert E. Miller Committee Member Davide A. Hill Committee Member Paul J. McGinn Committee Member Robert Nerenberg Committee Member Y. Elaine Zhi Committee Member Keywords
- Fuel Cells
- Nuvant
- Support Modifications
- Pulsed Electrodeposition
- PtCo
- Pt
- Catalyst Moropholgy
Date of Defense 2007-08-22 Availability unrestricted Abstract Possible enhancement of low temperature polymer electrolyte membrane fuel cells (PEMFC) or direct methanol fuel cells (DMFC) was investigated by modifying catalyst and support layers. Platinum (Pt) and platinum cobalt (PtxCo1-x) alloys were prepared by pulsed electrodeposition onto Toray carbon paper. Composite supports composed of either commercial multi-walled nanofiber (MWNF) mats or MWNF layers on a commercial backing were also investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and energy dispersive x-ray (EDX) were used to characterize the surface structure, composition, and catalyst loading. Various electrochemical techniques with a wet electrochemical cell, a Nuvant multi-array system, and a Scribner fuel cell system were used to study and rank the effectiveness of the catalysts and supports toward both the methanol oxidation reaction and the oxygen reduction reaction.The activity toward methanol oxidation of the electrodeposited Pt catalyst was found to be dependent on the deposited mass. Further comparisons between commercial
electrodes in the Nuvant system showed these deposits can yield activities comparable to those of commercially available electrodes. The structure of the Pt electrodeposits was highly non-uniform due to the H2 evolution during the deposition process blocking the cathodes surface. The activities of the planar structured PtxCo1-x deposits were insignificant for both oxygen reduction and methanol oxidation. The composition of the deposits ranged from 5 to 15 at% Pt. It was found by both the Nuvant and Scribner systems that the addition of a thin hydrophilic MWNF layer to a hydrophobic electrode would enhance the performance of a DMFC anode. In the Nuvant system, the addition of a thin hydrophilic MWNF layer to a hydrophobic electrode also enhanced the PEM cathode activity. This however was not corroborated by Scribner analysis, showing a performance below that of commercially available electrodes.
The best prepared electrode for the anode in a DMFC consisted of a pulse plated Pt catalyst loading of ~0.2 mg cm-2 and a composite support with a 2.0 mils PSF MWNF layer on a hydrophobic ELAT 2500LT backing. The best composite electrode for the cathode in a PEM fuel cells consisted of a 0.1 mil PSF MWNF layer on ELAT 2500LT backing.
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