Thesis (M. Phil.)--University of Hong Kong, 1979.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

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published_or_final_version / Chemistry / Master / Master of Philosophy

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Hydrogen is considered to be the fuel of the future as it is clean and abundant. Together with the rapidly developing fuel cell technology, it can sustain an environmentally sound and efficient energy supply system. Developing the technologies of palladium-based membrane for hydrogen separation and palladium nanostructured materials for hydrogen sensing and hydrogenation catalysts makes the "hydrogen economy" possible. This is because these technologies will allow for commercially viable production of comparatively cheap and high-quality hydrogen, and safety of its application. Based on the market requirements and interest in the development of a hydrogen economy, the purposes of this thesis are to develop thin palladium membrane for hydrogen separation and to explore an economic method for the synthesis of palladium nanowires in potential engineering applications. The original contributions of this thesis are outlined below: / The investigation of deposition progress of a palladium membrane on porous stainless steel substrate illustrates that palladium deposits will form a network structure on pore areas of the substrate surface in the initial stages. A bridge model is presented to describe the formation of a membrane. This model is confirmed from the cross-section of the deposited membranes. Based on the bridge model and the experimental measurements of palladium membranes deposited on the pore area of the substrates, the thickness of a palladium membrane deposited on 0.2 mum grade porous stainless steel substrate can be effectively controlled around 1.5∼2 mum, and the thickness of a palladium membrane deposited on 2 mum grade porous Inconel substrate can be effectively controlled around 7.5∼8 mum. Comparing the thickness and quality of palladium membranes deposited on the same substrates with the data in the literature, the thicknesses of the membranes prepared in this program are lower. The obtained result will be beneficial in the design and manufacture of suitable membranes using the electroless deposition process. / In the initial deposition stages, palladium nanoparticles cannot be deposited at the surface of the SiO2 inclusions that appear at the substrate surface. With the extension of deposition time, however, palladium nanoparticles gradually cover the SiO2 inclusions layer by layer due to the advance deposited palladium nanoparticles on the steel substrate surrounding them. The effect of the SiO2 inclusions on palladium deposits cannot be neglected when an ultra-thin membrane having the thickness similar to the size of inclusions is to be built. / The chemical reaction between phosphorus (or phosphate) and palladium at high temperature can take place. This reaction causes surface damage of the membranes. If palladium membranes are built on the porous substrates that contain phosphorus or phosphate used in the inorganic binders, they cannot be used over 550°C. This result also implies that palladium membranes cannot be employed on the work environment of phosphorus or phosphates. / Palladium nanowires are well arranged by nanoparticles at the rough stainless steel surface. The formation procedures consist of 3 stages. In the initial stage, palladium nanoparticles are aligned in ore direction, then the nanowire is assembled continuously using follow-up palladium deposits, and finally the nanowire is built smoothly and homogeneously. It is also found that palladium nanoparticles generated from the autocatalytic reaction are not wetting with the steel substrate and they are not solid and easily deformed due to the interfacial tension when they connect to each other. / Various palladium nanowire arrays possessing the morphologies of single wires, parallel and curved wires, intersections and network structures are illustrated. The results demonstrate that palladium nanowires can be built in a self-assembled manner by palladium nanoparticles in the initial deposition stages. Such self-assembled nanowires may attract engineering applications because electroless deposition process and preparation of a substrate are simple and inexpensive. / The diameter of palladium nanowires can be effectively controlled by the concentration of PdCl2 in the plating solution and deposition time. The size of palladium nanoparticles generated from the autocatalytic reaction is directly dependent on the concentration of PdCl2 in the plating solution. The higher the concentration of PdCl2 in the plating solution is, the smaller the deposited palladium nanoparticles are. The experimental results provide a controllable method for the fabrication of palladium nanowire arrays with potential engineering applications.

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