Authors: Ryan Yarbrough
Source:  (article, 2020-01-01)
Field: Materials Science — Materials Chemistry

Metal oxide nanostructures for thermoelectric materials: experimental and computational materials performance evaluation Waste recovery technologies, which convert heat into usable energy can meet the global demand for energy. One solution to this issue is thermoelectric generators (TEGs), which converts heat into electricity. However, several aspects of current TEGs need radical improvement before they can compete with incumbent technologies. The commercially available TEGs operate at a low efficiency, are made from expensive, toxic, and rare materials, and very are very expensive with a low Return on Investment. Metal oxides are an emerging set of materials that could perhaps overcome these drawbacks. The properties of metal oxides can further be tailored and fine-tuned by nanostructuring them, resulting in freezing phonon modes and reducing the materials thermal conductivity. This dissertation research aims at investigating the thermoelectric properties (TE) of metal oxides nanostructures and compared their TE properties with TE properties of their bulk form powder materials, which define as having sizes above 100 nm in all dimensions. To do this, a new rapid designing and testing approach is developed by coupling a computational framework, which screens metal oxides with promising TE properties, with an experimental approach, which synthesize and evaluate TE properties of metal oxides nanostructuresand compared their thermoelectric properties with their counterparts of powder materials. Utilizing Density Functional Theory, (DFT) a computational approach is developed and can be used to rapidly predict the thermoelectric properties of most crystalline materials, enabling rapid screening of potential metal oxides candidates. A sol-gel method is developed to make nanomaterials of metal oxides. The effects of the solvent type and base concentration on nanomaterials? morphologies and crystallinity are investigated by making five different metal oxides; Manganese Oxide, Magnesium Hydroxide, Copper Oxide, Chromium Oxide, and Strontium Oxide. Combining experimental and computational methods, a comprehensive analysis of the thermoelectric properties for Manganese Oxide (Mn3O4) nanoparticles and MnO2 bulk powder is performed and compared with TE properties of its derivatives, Mn3O4, and MnO2. At the initial stages of evaluating the thermoelectric properties of manganese oxide, the pressed pellets of both Mn3O4 powder and its nanoparticle form were electrically insulating but showed a significantly high Seebeck coefficient in the range of 0.2 to 2 mV/K for the nanoparticles and 0.4 and 1.4 mV/K for the powder form, which is close to accepted values in literature. The TE properties of MnO2 predicted using the computational framework developed in this work further confirmed its validity and shows potential of applying the method to TE materials screening for other inorganic oxides and dichalcogenide. Materials science ; Thermoelectric effect ; Thermoelectric materials ; Nanotechnology ; Nanomaterials ; Oxide ; Thermoelectric generator ; Waste heat ; Nanostructure ; Thermal conductivity ; Mechanical engineering ; Metallurgy ; Composite material ; Thermodynamics Chemical and Physical Properties of Materials