Date of Award

8-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemistry

Committee Member

Dr. Stephen E. Creager, Committee Chair

Committee Member

Dr. George Chumanov

Committee Member

Dr. William T. Pennington

Committee Member

Dr. Joseph S. Thrasher

Abstract

This dissertation describes research on the development, preparation, and characterization of advanced cathode materials for use in proton-exchange membrane fuel cells (PEMFC). In addition, the development of electroanalytical testing tech-niques for the characterization of PEMFC materials is discussed, including a method to independently measure ionic and electronic conductivities in thin films. Commer-cially available Vulcan-XC72 was modified with zirconia (ZrV) via a condensation reaction. Platinum catalyst nanoparticles were homogeneously deposited onto the surface of the ZrV support. The materials (Pt/ZrV) were then treated with various small molecules containing phosphonate groups that selectively bound to the surface of the zirconia through robust Zr-O-P chemical bonding. These materials were char-acterized with X-ray powder diffraction (XRPD), transmission electron micrscopy (TEM), scanning electron micrscopy (SEM), N2 physisorption analysis, ex situ and in situ cyclic voltammetry, etc. The in situ cyclic voltammtery measurements were performed in a micro fuel cell. The fabrication and validation of the micro fuel cell are discussed. Additionally, single-cell testing was performed on the modified Pt/ZrV samples. Proton-exchange membrane fuel cells are complicated systems. The perfor-mance, as indicated by area-normalized cell current and power, is governed by many transport mechanisms, including ion, electron, and reactant gas transport. Optimization of one transport property often opposes the others, making the PEMFC perfor-mance optimization a delicate balance of parameters. Modifying the surfaces of cata-lyst materials with di-acid species, such as m-sulfophenylphosphonic acid (mSPPA), should provide additional sites for proton conduction, while achieving a high electronic conductivity from the catalyst support, and good transport of reactant gas species from the porosity of the carbon. The hope is to increase the three-phase (ions, elec-trons, gases) contact zone in electrode and stability of the electrode through surface modification.

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