| In the field of catalysis, the development of alternative catalysts for the oxygen reduction reaction (ORR) in Polymer Electrolyte Membrane Fuel Cell (PEMFC) cathodes has been an ongoing task for researchers over the past two decades. PEM fuel cells are considered to be potential replacements for internal combustion engines in automobiles, and their reduced emissions and better efficiency would have huge payoffs for our environment, and in reducing our nation's dependence on foreign oil. To date, PEMFC cathode over-potentials are still significant, and the only materials discovered to be highly active and stable catalysts in an acidic environment are platinum-based. Despite several major advances in recent years in reducing platinum loading in fuel cell electrodes, the high expense and low availability of platinum will hinder the large-scale commercialization of PEM fuel cells. The most hopeful advances being made in replacing platinum are related to pyrolyzed organic macrocycles with transition metal centers (such as Fe or Co porphyrins and phthalocyanines). Encouragingly, it has recently been discovered that active electrodes could be prepared by heat-treating metal and nitrogen precursors (not necessarily organic macrocycles) together in the presence of a carbon support.; In the first study of this dissertation, catalysts for the Oxygen Reduction Reaction (ORR) were prepared by the pyrolysis of acetonitrile over various supports. The supports used included Vulcan Carbon, high purity alumina, silica, magnesia, and these same supports impregnated with Fe, Co, or Ni in the form of acetate salt. The catalysts were characterized by BET surface area analysis, BJH Pore Size Distribution (PSD), conductivity testing, Transmission Electron Microscopy (TEM), Temperature Programmed Oxidation (TPO), Thermo-Gravimetric Analysis (TGA), X-Ray Diffraction (XRD), X-ray Photo-electron Spectroscopy (XPS), Mossbauer Spectroscopy, Rotating Disk Electrode (RDE) half cell testing, and full PEMFC testing. The most active catalysts were formed when Fe was added to the support before the pyrolysis; however, samples in which no metal was added still showed elevated activity for oxygen reduction. The alumina-based samples showed the best activity, although they were less conductive, even after exposed alumina was dissolved away with hydrofluoric acid. Within a support family, the more active catalysts had a higher amount of pyridinic nitrogen, as determined from XPS. A theory has been proposed to explain this trend based on the formation of different nano-structures depending on which support material is used for the acetonitrile decomposition. According to this theory, nitrogen-containing carbon samples with nano-structures that result in more edge planes being exposed (the plane in which all pyridinic nitrogen is found) will be more active for the ORR. Recommendations for further research in this area are presented.; In volume II of this dissertation, Cu-based catalysts for hydrogen production from methanol and water were studied. These catalysts have applications for mobile fuel cells that rely on hydrogen production from easier to store liquid fuels, such as methanol. |
