Studies of some technologically important interfaces.

摘要

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.;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.;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 (Sn 2-) 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.