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Mingzhe Yu PhD thesis.pdf (3.79 MB)

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Design and controlled synthesis of complex metal oxide nanostructures and study of their advanced energy applications

Yu, Mingzhe
http://rave.ohiolink.edu/etdc/view?acc_num=osu1448004174

Abstract Details

2015, Doctor of Philosophy, Ohio State University, Chemistry.
Nano-structured metal oxides are of significance for fundamental science and practical applications because of their widely tunable physiochemical properties and excellent stability under various conditions. The synthetic chemistry of metal oxide nanostructures with controlled properties and innovation of their device applications are two interesting and crucial topics towards large-scale industrial production and commercialization. The focus of this dissertation is on the design and controlled synthesis of wide-bandgap metal oxide semiconductor nanostructures and study of their device applications for electrocatalysis and photocatalysis. The controlled hydrothermal synthesis of p-type copper-based delafossite compounds (e.g. CuGaO2) and n-type titanium oxide (i.e., TiO2) on substrates are systematically studied. Their structural, chemical and optical properties are characterized via X-ray diffraction, electron microscopy, photoelectron spectroscopy and diffuse-reflectance spectroscopy. The obtained CuGaO2 and TiO2 nanostructures have been applied as semiconductor electrodes in p-type dye-sensitized solar cells, lithium-air and lithium-iodine solar batteries. A combination of absorption spectroscopy, electro-analytical techniques and photoelectrochemical methods are employed to evaluate the materials’ electrochemical and electronic performance within different device configurations. Obtaining delafossite CuGaO2 nanoparticles is challenging but desirable for high-surface area device applications such as dye-sensitization and trace gas detection. The phase formation and crystal growth mechanism of delafossite CuGaO2 under low-temperature hydrothermal conditions are studied. The stabilization of CuI cations in aqueous solution and the controlling of the hydrolysis of GaIII species are found to be the two crucial factors that determine the phase formation. The oriented attachment (OA) growth is proposed as the crystal growth mechanism to explain the formation of large CuGaO2 nanoplates. Delafossite CuGaO2 nanoparticles on a 20 nm-size have been successfully synthesized for the first time. The synthesized light-colored CuGaO2 is applied as photocathodes in p-type dye-sensitized solar cells for the first time and presents significantly higher photovoltage compared to conventional NiO-based solar cells. Under 1 Sun AM 1.5 illumination, a Voc of 357 mV has been achieved, which is among the highest values that have been reported for p-DSSCs. Well-aligned TiO2 nanorods on stainless steel and titanium substrates and nano-particles are synthesized through the hydrothermal process under controlled acidic conditions. The dye-sensitized TiO2 nano-structures have been applied as photoelectrodes in solar-powered electrochemical energy storage devices (i.e., solar batteries), for the simultaneous conversion and storage of solar energy. The solar battery integrates a photo-electrochemical cell and an electrochemical cell into a single device and is able to harvest solar energy and store it in-situ within the device via a photocharging process and distribute the energy as electric power when needed. A lithium-oxygen (Li-O2) solar battery is demonstrated with a dye-sensitized TiO2 photoelectrode. A triiodide/iodide redox shuttle is used to couple a built-in nano-structured photoelectrode with the oxygen air electrode for the photo-assisted charging of a Li-O2 battery. On charging under illumination, triiodide ions are generated on the photoelectrode, and subsequently oxidize Li2O2. Because of the contribution of the photovoltage, a “negative” charging overpotential appears. The introduction of the TiO2 photoelectrode here offers a novel strategy to address the overpotential issue of current non-aqueous Li-O2 batteries. Another lithium-iodine (Li-I) solar flow battery (SFB) has also been constructed with integrating the TiO2 semiconductor photoelectrode with a Li-I redox battery. During the photo-assisted charging process, I- ions are photoelectrochemically oxidized to I3-, harvesting solar energy and storing it as chemical energy. The Li-I SFB can be charged at a voltage of 2.90 V under 1 sun AM 1.5 illumination, which is lower than its discharging voltage of 3.30 V. The charging voltage reduction translates to energy savings of close to 20% compared to conventional Li-I batteries.
Yiying Wu (Advisor)
190 p.
Chemistry; Materials Science

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Citations

  • Yu, M. (2015). Design and controlled synthesis of complex metal oxide nanostructures and study of their advanced energy applications [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1448004174

    APA Style (7th edition)

  • Yu, Mingzhe. Design and controlled synthesis of complex metal oxide nanostructures and study of their advanced energy applications. 2015. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1448004174.

    MLA Style (8th edition)

  • Yu, Mingzhe. "Design and controlled synthesis of complex metal oxide nanostructures and study of their advanced energy applications." Doctoral dissertation, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1448004174

    Chicago Manual of Style (17th edition)

osu1448004174
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This open access ETD is published by The Ohio State University and OhioLINK.