Vertically Ordered Nanostructures for Energy Harvesting and StorageDesai, Umang (2013) Vertically Ordered Nanostructures for Energy Harvesting and Storage. Doctoral Dissertation, University of Pittsburgh. (Unpublished)
AbstractVertically ordered (1-D) nanostructures provide a promising alternative to conventional nanoparticle films used as electrode materials for energy conversion and storage devices. These 1-D nanostructures, in forms of nanowires or nanotubes, promote mass transfer and accessibility of the electrodes while providing a direct conduction path for electrons. Our work has been focused on synthesis and application of novel 1-D nanostructures for dye-sensitized solar cells (DSCs) and lithium-ion batteries (LIBs). The vertically aligned 1-D nanostructures are employed in DSCs to overcome the limitation of nanoparticle-based DSCs. Much longer electron life time has been observed in DSCs based on 1-D nanostructures compared to the nanoparticle-based ones, which allows us to use thicker sensitized film to improve the efficiency. We have developed a facile low-temperature hydrothermal method to synthesize vertically aligned ZnO nanowire arrays directly on transparent conductive oxide, and to use the ZnO nanowire arrays as a template to synthesize SnO2 nanotube arrays. In addition, we have developed a convenient approach that involves alternate cycles of nanowire growth and self-assembled monolayer coating processes for synthesizing multilayer assemblies of 1-D nanostructures with ultrahigh internal surface areas. The vertically aligned nanostructure also enables us to fabricate high-efficiency solid-state DSCs by replacing the liquid electrolyte with a solid hole transporting material. The vertically aligned nanostructures provide straight channels for filling the solid electrolyte, enabling the use of thicker photoanodes for solid-state DSCs. Significantly, by using vertically aligned multilayer arrays of TiO2-coated ZnO nanowires, liquid-electrolyte DSCs with power conversion efficiency up to 7.0% and solid-state DSCs with efficiency up to 5.65% have been obtained. Vertically ordered 1-D nanostructures also offer remarkable advantages for rechargeable LIBs including fast electron transport/collection and ion diffusion, enhanced electrode-electrolyte contact area, and facile accommodation of strains caused during the charge and discharge cycles. We have developed a method to fabricate SnO2 nanotube arrays and hybrid Sn-based nanotube arrays directly on current collecting substrate (Ti) and have evaluated their performance as anodes in rechargeable LIBs. The hybrid Sn-based nanotube arrays synthesized by us delivered a capacity of 710 mAh/g after 80 cycles with a low capacity fade. Share
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