When 11:30 AM - 1:30 PM Jan 25, 2016
Where 2000A Phoenix Memorial Lab
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Controlling Nanostructure for Catalytic and Electrochemical Energy Storage Materials


Tapiwa Mushove
Thesis Defense

Levi Thompson and Katsuyo Thornton, advisors.

 

Materials with precisely controlled nanostructures are needed to significantly enhance the efficiencies of next-generation chemical conversion and energy storage systems. This dissertation employs photo- and electrochemical synthesis techniques to control nanostructure for catalytic and electrochemical energy storage materials. We also define nanostructure-function relationships for three material systems. The ultimate goal was to develop design rules for the synthesis of materials with superior performance.

 

Single layer, multilayer, and wave-like hematite nanotube arrays with controlled structure and dimensions were fabricated via the electrochemical anodization of high-purity iron foils. During fabrication, the current response of the films was tracked to characterize the growth process. Four distinct stages were identified with regard to the evolution of the nanotube arrays: an ohmic response stage, an oxide film formation stage, a chemical dissolution stage, and a steady-state growth stage. Morphological, optical, and photoelectrochemical properties of the hematite electrodes were characterized and correlated with their photoelectrochemical water oxidation performances. Charge carrier transport and the active electrochemical surface area of the different morphologies played a key role with regard to the photocatalytic performance.

 

Next, niobium pentoxide (Nb2O5) nanotube array and planar electrodes were fabricated by varying the synthesis conditions during electrochemical anodization. The Li+ ion intercalation behavior of the electrodes was characterized. Nb2O5 nanotube arrays exhibited a four-fold improvement in the charge storage capacity and faster ion diffusion when compared to planar electrodes. Electrochemical performance differences between the two morphologies were a result of increased surface areas, and shorter ion diffusion lengths in the nanotube arrays.

 

Finally, light of varying wavelengths was used to control the photodeposition of noble metals on tungsten trioxide. The noble metal particle sizes and total metal loadings were strong functions of the illumination time, while the nanoparticle geometry was controlled by the illumination wavelength. Intrinsic variations in the plasmonic responses of the noble materials across the UV-vis spectrum allowed for control of the nanoparticle geometries. These photodeposited materials were evaluated for the selective hydrogenation of crotonaldehyde, a model α,β-unsaturated aldehyde, and the results were correlated with key nanostructural properties of the noble metal particles.