Part I: Synthesis and characterization of titania and magnesium nanoparticles for hydrogen production and storage. Part II: Characterization and growth of branched silicon nanowires grown via a simultaneous vapor-liquid-solid and vapor-solid-solid mechanism.

摘要

A single pot synthesis has been developed in our lab to produce 5 nm dyed-platinized TiO2 nanoparticles for hydrogen production. The particles produce hydrogen with Pt and Ru amounts as low as 0.15 wt%. and 0.02 wt%, respectively. Even with such low amounts the material exhibits significant increase in the catalysis of water splitting. The synthesis, characterization and hydrogen producing properties are described in Chapter 1.;Chapter 2 is adapted from a published book chapter and gives a broad overview of the use of Mg for hydrogen storage. It covers several methods of synthesizing Mg nanomaterials and the effects that various dopants have on its hydrogen storage properties. The chapter also specifies different techniques in which hydrogen storage properties can be analyzed. The Ni doped Mg nanoparticles mentioned in Chapter 2 was developed and studied in the Prieto lab and some of the work done thus far is detailed in Chapter 3. The Ni doped Mg nanoparticles are of particular interest because of the unexplained increase in hydrogen sorption kinetics. Sorption kinetics are expected to decrease after cycling due to particle agglomeration. However, Ni doped Mg particles exhibit an increase in performance after several cycles. For this reason, an in depth analysis of the material and it's kinetic behavior has been performed. Although hydrogen is a promising method of storing solar energy harnessed by the use of TiO 2 photocatalysts, other routes, such as batteries, need also be explored.;The initial synthesis of the branched silicon nanowires was a serendipitous event. The branched wires were originally observed whilst experimenting with the feasibility of growing Cu2Sb nanowires via a Vapor-Liquid-Solid (VLS) mechanism. The compound Cu2Sb is a Li-ion battery anode material that is of major interest in the Prieto group. The end goal was to produce high purity low defect crystals of Cu2Sb nanowires that could be cycled and the lithiation and de-lithiation of the material could be well characterized without the effects of impurities or crystal defects. However, during the attempted synthesis of this compound, the growth of highly branched silicon nanowires was observed. The branched wires were characterized and the once serendipitously grown wires are now reproducible. Chapter 4 includes the characterization and initial proposed growth mechanism. My contribution to this project has been to improve upon the growth parameters and further understanding of the growth mechanism. Many assumptions had been made about the growth process and the roles of many growth parameters were misinterpreted, understating the importance of the parameters toward the wire growth. It was determined that the Au catalyst initially used to grow the branched wires was not necessary for wire growth and also detrimental to the yield of branched wires. Using only Cu as a catalyst increases the yield of the branched wires. However, the substrates must be properly treated prior to the reaction in order for Cu to deposit on the substrate to initiate wire growth during the reaction. Chapter 5 includes an in-depth study of substrate preparation and conditions necessary for branched Si nanowire growth. If copper is to be used as catalysts for the growth of Si nanowire arrays, the interaction within the Cu-Si system need to be well characterized. Chapter 6 entails a description of the properties of the branched Si nanowires that expose interesting characteristics unique to the Cu-Si system. The unique interaction of Cu and Si allows for the growth of these novel nanostructures. The growth mechanism depends on the combination of the crystalline orientation of wire growth, defects within the crystal, and the fast diffusion of Cu into these defects, Although not fully confirmed, the proposed growth mechanism may aid in the development of clever ways to grow complex nanowire arrays for use as photovoltaics. (Abstract shortened by UMI.).