Conducting polymers, metal oxides, and their effects on the oxidation of organic fuels at Pt or Pd

Abstract

The ideas explored in this thesis originate from the significant role of the support material in the performance of anodes in organic fuel cells. This text describes a variety of approaches to provide insight into the synthesis, structure, and roles of various supports in organic fuel oxidation at Pt or Pd. -- Potentiodynamic, potentiostatic, and galvanostatic regimes were used to polymerize pyrrole on carbon black (CB) electrodes. It was found that the electrochemical properties and structures of the CB/polypyrrole composites (PPCB) depended on the polymerization conditions. While potential-controlled polymerization regimes produced resistive PPCB films, constant current polymerization resulted in PPCB composites with high conductivity over a wide potential range. -- Potentiodynamic, potentiostatic, and galvanostatic regimes were used to polymerize pyrrole on carbon black (CB) electrodes. It was found that the electrochemical properties and structures of the CB/polypyrrole composites (PPCB) depended on the polymerization conditions. While potential-controlled polymerization regimes produced resistive PPCB films, constant current polymerization resulted in PPCB composites with high conductivity over a wide potential range. -- A methodology was developed to study support effects, based on the use of polyaniline (PANI) or various metal oxides (MOs) on glassy carbon (GC) as supports for organic fuel oxidation at Pt and Pd nanoparticles. Methanol oxidation at a GC/Ru oxide/Pt electrode was compared to GC/Pt, while a GC/PANI/Pt electrode did not show any enhancement. The same GC/PANI support (made in 0.1 M H₂SO₄), and also GC/PANI electrodes made in two other media (CF₃COOH and CF₃SO₃H), coated with Pd nanoparticles gave lower onsets and higher FA oxidation currents than at GC/Pd, providing unambiguous evidence for effects of PANI on this reaction at Pd. The method was further extended to ethanol oxidation at Pt supported on various MOs, where InSn oxide/Pt, GC/Ru oxide/Pt, GC/Sn oxide/Pt, and GC/RuSn oxide/Pt electrodes were superior to GC/Pt at all potentials. Sn oxide was effective at low potentials (E < +0.4 V/SCE), resulting in higher activities of the Sn oxide-containing electrodes over this range. At more positive potentials GC/Ru oxide/Pt gave superior activity due to the effectiveness of Ru oxide for CO oxidation.