published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

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As a material whose applications are many and growing, zinc oxide still remains a complex system whose photoluminescent (PL), structural, electrical, and photocatalytic properties have not been fundamentally understood. The luminescent properties of zinc oxide (ZnO) nanocrystals (NCs) are very sensitive to crystal structure, and defect states in zinc oxide, which in turn is very sensitive to preparation methods, post-synthesis workup, and thermal treatments. Understanding and managing this rich defect chemistry is critical to controlling ZnO properties. As the surface-to-volume ratio of ZnO increases as materials enter the quantum regime, the surface defects play a stronger role. The exact role of the defect states and their contribution to the physical and chemical properties of ZnO has been studies in great lengths yet still remains controversial.

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A numerical model for solid oxide fuel cells with Ni-infiltrated porous anode has been described. The novel contribution of the work is the development of a semi-continuous film model to describe the infiltrated Ni-phase. This model relates experimentally controllable parameters, namely, Ni- loading, porosity and pore size to the effective electronic conductivity of the Ni-phase and the number of active reaction sites or the triple phase boundary (TPB). The semi-continuous film model was incorporated in a two-dimensional (2D) SOFC model. The 2D model considers the coupled gas-phase transport, charge transport and electrochemical kinetics to directly examine the effect of Ni loading and porosity on the electrochemical performance of Ni-infiltrated SOFC anodes. From the semi-continuous film model, an optimal Ni loading that corresponds to a maximum in TPB length was identified. Comparison of effective electronic conductivity and TPB length for a Ni-infiltrated anode with those for a composite Ni-YSZ anode suggests that an infiltrated Ni anode with adequate electrical conductivity and sufficiently high TPB length can be fabricated even at a very low Ni loading. Comparison of various porous anodes with varying Ni loading, it was determined that maximum electrochemical performance does indeed correspond to anode with maximum TPB length. It was also determined that an infiltrated anode will have higher performance capabilities when compared to the conventional composite electrodes. However, degradation of performance may result due to degradation of connectivity in the infiltrated Ni. The methodology to model the latter effect was also proposed. / Thesis (Master, Chemical Engineering) -- Queen's University, 2012-06-13 13:09:49.182