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Title page for ETD etd-07202015-161501

Type of Document Dissertation
Author Brodt, Matthew Ward
Author's Email Address matthew.w.brodt@vanderbilt.edu
URN etd-07202015-161501
Title Electrospun Nanofiber Electrodes for Hydrogen/Air Proton Exchange Membrane Fuel Cells
Degree PhD
Department Chemical Engineering
Advisory Committee
Advisor Name Title
Peter N. Pintauro Committee Chair
David E. Cliffel Committee Member
G. Kane Jennings Committee Member
M. Douglas LeVan Committee Member
  • fuel cells
  • cathodes
  • electrospinning
  • nanofiber electrodes
  • electrospun electrodes
Date of Defense 2015-07-15
Availability unrestricted
Nanofiber particle/polymer cathode mats, with an average fiber diameter in the 400-600 nm range, were fabricated by electrospinning mixtures of a proton exchange polymer and commercial Pt/C catalyst particles, incorporated into membrane-electrode-assembles (MEAs), and evaluated in a fuel cell test fixture. Nanofiber cathodes with a commercial Pt/C catalyst and a binder of Nafion and poly(acrylic acid) (PAA) were shown to work extremely well in hydrogen/air fuel cell MEAs. As compared to conventional painted cathode MEAs, they had a higher electrochemical surface area (39-45 m2/g for nanofibers vs. 30-36 m2/g for painted), higher mass activity (~0.16 A/mgPt vs. 0.11 A/mgPt), and higher power output (e.g., 396 mW/cm2 at 0.65 V with H2/air at ambient pressure and a cathode Pt loading of 0.10 mg/cm2 vs. 292 mW/cm2). MEA power output with nanofiber cathodes was insensitive to changes in fiber diameter and Nafion/PAA binder composition, indicating that precise control of these parameters is not required for commercial scale-up. The nanofiber electrode architecture did not significantly change the way fuel cell cathodes degraded during load cycling tests (Pt dissolution tests), but the nanofibers had a clear advantage in power retention after accelerated durability tests that simulate start-stop cycling (carbon corrosion tests). A second generation of nanofiber cathodes was fabricated with a binder of Nafion and poly(vinylidene fluoride) (PVDF). The addition of PVDF altered the hydrophilicity/hydrophobicity of the cathode and slowed the deleterious effects of carbon corrosion. Carbon corrosion rates were the same for both nanofiber and painted Nafion/PVDF cathodes, but the effect of corrosion on power output was much less severe for nanofiber cathodes. Cathodes with a low Nafion/PVDF ratio produced low power initially but the power density increased over the course of a carbon corrosion test. This unusual result was associated with the formation of hydrophilic carbon oxidation species at the catalyst support surface, which increased the hydrophilicity of the cathode.
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