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Mathematical modeling helps researchers to understand the transport and kinetic phenomena within fuel cells and their effects on fuel cell performance that may not be evident from experimental work. In this thesis, a 2-D steady-state cathode model of a proton-exchange-membrane fuel cell (PEMFC) is developed. The kinetics of the cathode half-reaction were investigated, specifically the reaction order with respect to oxygen concentration. It is unknown whether this reaction order is one or one half. First- and half-order reaction models were simulated and their influence on the predicted fuel cell performance was examined. At low overpotentials near 0.3 V, the half-order model predicted smaller current densities (approximately half that of the first-order model). At higher overpotentials above 0.5 V, the predicted current density of the half-order model is slightly higher than that of the first-order model. The effect of oxygen concentration at the channel/porous transport layer boundary was also simulated and it was shown the predicted current density of the first-order model experienced a larger decrease (~10-15% difference at low overpotentials) than the half-order model. Several other phenomena in the cathode model were also examined. The kinetic parameters (exchange current density and cathode transfer coefficient) were adjusted to assume a single Tafel slope, rather than a double Tafel slope, resulting in a significant improvement in the predicted fuel cell performance. Anisotropic electronic conductivities and mass diffusivities were added to cathode model so that the anisotropic structure of the porous transport layer was taken into account. As expected, the simulations showed improved performance at low current densities due to a higher electronic conductivity in the in-plane direction and decreased performance at high current densities due to smaller diffusivities. Additionally, the concentration overpotential was accounted for in the model; however it had little influence on the simulation results. / Thesis (Master, Chemical Engineering) -- Queen's University, 2008-09-19 12:14:29.079

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This dissertation addresses the synthesis of oriented mesoporous ceramic films by evaporation induced self-assembly of surfactants and ceramic precursors in films dip coated from ethanol-rich sols. First, the kinetics of silica polycondensation in surfactant templated sol-gel films is studied both before and after deposition using infrared spectroscopy. These observations reveal an induction time (with minimal condensation rate) before curing begins in certain surfactant-templated silica films, which can be utilized to perform post-synthesis modification. This induction time is maximized at high humidity, and by long nonionic surfactant headgroups (rather than, for instance, a trimethylammonium headgroup). The second part of the dissertation addresses lattice Monte Carlo (MC) simulation of the effects of confinement on the 2D hexagonally close packed (HCP) phase formed by 60 vol% surfactant in a polar solvent. The effects of size and type of confining geometry (slit, cylindrical and spherical cavities) and of surface chemistry are simulated. The HCP mesophase orients orthogonal to chemically neutral surfaces which attract both head and tail of the surfactant equally. Novel mesophase geometries are simulated including radially oriented micelles, concentric helices, and concentric porous shells. Utilizing fundamental insights from the kinetics and MC studies, the third part of the dissertation describes the synthesis of silica films with orthogonally tilted HCP mesophase on chemically neutral surfaces. Crosslinking a random copolymer of polyethylene oxide (PEO)-polyproplyene oxide (PPO) on glass slides results in chemically neutral surfaces for the PEO-PPO-PEO triblock copolymer template (P123) used here. The orthogonal orientation of the HCP channels is confirmed using advanced x-ray scattering techniques and electron microscopy. The final part of the dissertation discusses applications of ceramic films with orthogonally tilted (ortho-) HCP mesophase. Silica membranes with ortho-HCP pores are prepared on porous alumina supports, and show permeability of ethanol orders of magnitude greater than films with parallel-oriented HCP channels. Size-selective filtration of gold nanoparticles confirms the absence of any nanoscale cracks in the membranes. For a second application, we prepare titania films with ortho-HCP mesopores. Careful crystallization of the films followed by spinning on an organic hole conducting polymer (P3HT) leads to active bulk heterojunction solar cells.

The purpose of this study was to examine the effects of body mass and sex on the joint biomechanics of the lower extremity during stair ascent and descent. Nineteen normal weight (8M and11F; BMI: 22.1 ± 1.8 kg/m2), 18 overweight (14M and 4F; BMI: 27.4 ± 1.3 kg/m2) and 8 obese subjects (3M and 5F; BMI: 33.3 ± 2.5 kg/m2) were recruited. Joint mechanical loading presented by joint moment of force and peak joint angles at the hip, knee, and ankle during stair climbing were recorded and analyzed using a motion analysis system with 10 cameras and 4 force plates. The MANOVA and linear regression analysis found a significantly larger knee extensor moment (p=0.026) among the overweight compared to the normal weight participants during descent. Sex differences were found in the peak joint angles, as the females abducted their knees more than the males (p=0.002; r(51) = 0.51) during descent.

Non-equilibrium boundary conditions based upon kinetic theory and linear irreversible thermodynamics are applied to the interface kinetics in vapor crystal growth of unitary and binary materials. These are compared to equilibrium boundary conditions in a simple, 1D closed ampoule physical vapor transport model. It is found that in cases where the diffusive impedance is negligible and when system pressure is low, surface kinetics play an important role in limiting the mass transport. In cases where diffusion is the dominant transport impedance, and/or when the pressure in the system is high, the kinetic impedances at the interfaces are negligible, as impedances due to diffusion and latent heat transport at the interfaces become more significant. The non-equilibrium boundary conditions are dependent upon the sticking coefficient of the surface. An experiment to estimate the sticking coefficient on solid surfaces is proposed. The non-equilibrium theory also predicts significant temperature jumps at the interfaces. / Graduate