UBC Theses and Dissertations
Studies of some technologically important interfaces Teo, Mark Yu Chao
This thesis discusses surface and interfacial investigations for two technologically important areas. The first area focuses on surface modification of oxidized high-purity aluminum for improved interfacial bonding with an organosilane, bis-1,2-(triethoxysilyl)ethane (BTSE), for adhesion promotion and corrosion protection. BTSE adsorption onto various pre-treated oxidized aluminum surfaces are compared. Secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to assess the effects of pre-treatment on the direct Al-O-Si covalent bonding and the strength of adhesive bonding. Applying a sulphuric-chromic (FPL--Forest Products Laboratory) pre-treatment to native oxide on high-purity Al generates a compact, well-anchored oxide layer with a surface that is effective for Al-O-Si bonding after BTSE coating. H₂ plasma pre-treatments improve BTSE chemisorption on FPL pre-treated Al surfaces. However, heat pre-treatments can modify a native Al oxide surface for increased adhesion with BTSE. The second area focuses on the use of transition metal chalcogen thin films and powders in oxygen reduction reaction (ORR) catalysis for proton exchange membrane (PEM) fuel cells. A novel combination of micro-Raman spectroscopy and scanning Auger microscopy (SAM) enabled the identification of different elemental compositions at local regions of a Co-Se thin film which led to a reinterpretation of Raman peaks reported previously. Raman characterization of sputtered Fe-S, Co-S and Ni-S thin film surfaces identified the respective disulfide structures and suggested the presence of polysulfides (Sn²⁻) which may contribute to an improved ORR catalytic activity when compared to the corresponding disulfide standard. A sputtered Co-Ni-S thin film containing (Co,Ni)S₂ solid solution with possible polysulfides showed an enhanced ORR catalytic activity compared with other samples. A method for synthesizing high-purity, crystalline CoSe₂ powder on high-area carbon support is established; its surface and bulk structures are confirmed by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), micro-Raman spectroscopy, XPS and SAM. CoSe₂ demonstrated significant ORR catalytic activity with an OCP of 0.81 V and higher current density than CoSe. CoSe₂, characterized by combining SAM and backscattered electron (BSE) imaging, was electrochemically modified via cyclic voltammetry to give a Se-rich surface to enhance its ORR catalytic activity.
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