Metal oxide electrocatalysts for alternative energy technologies

This dissertation focuses on the development of metal oxide electrocatalysts with varying applications for alternative energy technologies. Interest in utilizing clean, renewable and sustainable sources of energy for powering the planet in the future has received much attention. This will address the growing concern of the need to reduce our dependence on fossil fuels. The facile synthesis of metal oxides from earth abundant metals was explored in this work. The electrocatalysts can be incorporated into photoelectrochemical devices, fuel cells, and other energy storage devices. The first section addresses the utilization of semiconductors that can harness solar energy for water splitting to generate hydrogen. An oxysulfide was studied in order to combine the advantageous properties of the stability of metal oxides and the visible light absorbance of metal chalcogenides. Bi2O2S was synthesized under facile hydrothermal conditions. The band gap of Bi2O2S was smaller than that of its oxide counterpart, Bi2O3. Light absorption by Bi2O2S was extended to the visible region (> 600 nm) in comparison to Bi2O3. The formation of a composite with In2O3 was formed in order to create a UV irradiation protective coating of the Bi2O2S. The Bi2O2S/In2O3 composite coupled with a dye CrTPP(Cl) and cocatalysts Pt and Co3O4 was utilized for water splitting under light irradiation to generate hydrogen and oxygen. The second section focuses on improving the stability and light absorption of semiconductors by changing the shapes and morphologies. One of the limitations of semiconductor materials is that recombination of electron-hole pairs occur within the bulk of the materials instead of migration to the surface. Three-dimensional shapes, such as nanorods, can prevent this recombination in comparison to spherical particles. Hierarchical structures, such as dendrites, cubes, and multipods, were synthesized under hydrothermal conditions, in order to reduce recombination and improve photocatalytic activity. Another disadvantageous property of semiconductors is that photocorrosion of metal chalcogenides such as CdS occurs. In an attempt to prevent this, these materials were coated with more stable oxides such as Cu2O and TiO2. The photocatalytic activity of these CdS multipods protected by the stable oxides was enhanced in comparison to CdS particles. The third section describes the synthesis and the use of mixed metal oxides for alcohol oxidation. Presently, Pt is the most active and efficient metal catalyst for alcohol oxidation in fuel cells. It is necessary to develop cheaper, earth abundant metals that can replace Pt. Mixed metal oxides based on Mo-V-(Te,Nb)-O were synthesized under hydrothermal conditions. These materials were incorporated into an electrochemical cell and used to oxidize cyclohexanol. At low temperatures of 60 °C, cyclohexanol was converted to cyclohexanone, cyclohexene, and adipic acid on Mo-V-O, Mo-V-Te-O, and Mo-V-Te-Nb-O respectively. The present work showed that these interesting materials might potentially be utilized as a catalyst in complex alcohol fuel cell technologies. In the final section, the electrochemical actuation in conducting polymers is studied. Conducting polymers, such as polypyrrole (PPy), and polythiophene (PTh), are often incorporated into actuators, sensors, and energy storage devices such as supercapacitors. The mechanism of the actuation in these polymers due to the insertion/removal of ions was studied. Electrochemical quartz crystal microbalance (EQCM) studies and in situ electrochemical stress measurements were the techniques used to study and to understand the observed actuation mechanism. The bilayer polypyrrole/polythiophene (PPy PTh) polymer film showed potential for enhancing the actuation and capacitance in energy storage devices