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Microstructural and performance analysis of fuel cell electrodes
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- Author / Creator
- Sabharwal, Mayank
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Microscopy techniques have emerged as a powerful tool to study the morphology of fuel cell porous media. Mathematical parametrization of the microscopy images is important to characterize the porous media microstructure and compare the differences between various samples. A framework which can process microscopy images to generate a microstructure and perform statistical and functional characterization is necessary to streamline the process of going from images to performance.
This thesis presents an open-source numerical framework for microstructural analysis of fuel cell porous media. The framework can be used to: i) process raw data from microscopy images; ii) statistically characterize the microstructure using two-point correlation function, chord length function and pore size distribution; iii) generate stochastic reconstructions of porous media; iv) generate voxel based meshes; and v) study gas transport, charge transport and electrochemical reactions under dry and wet conditions.
The numerical tools developed in this thesis are used to analyze the effect of catalyst layer microstructure on the transport properties and electrochemical performance by studying the: i) effect of catalyst layer porosity and local saturation on the effective diffusivity; ii) effect of the catalyst layer pore size distribution on the electrochemical performance under dry and wet conditions; and iii) effect of ionomer content and distribution on the effective transport properties and electrochemical performance. Stochastic reconstructions are used to generate catalyst layers (CLs) with different microstructures for these studies.
Numerical simulations are used to study gas transport in CLs with different porosities and local saturations. Partially saturated CL reconstructions were obtained using a novel nucleation based water intrusion algorithm. The effective diffusivities computed for CLs with different porosities and local saturations are used to develop a correlation based on the percolation theory which was only dependent on the effective porosity and average pore radius of the CL.
Electrochemical simulations on CLs with different pore size distributions show negligible variations under dry conditions because mass transport is limited by the interfacial resistance of the ionomer film. Under wet conditions, the electrochemical performance initially remains constant and then decreases rapidly beyond a certain saturation due to pore blockage by liquid water. The results from the current study indicate that a CL with smaller and more hydrophobic pores would be better at delaying the onset of flooding in the CL and therefore, have a higher performance at a given capillary pressure.
CL reconstructions with different ionomer contents and distributions are generated using the ionomer reconstruction algorithm presented in this work. Results show that the ionomer distribution had a significant impact on the effective protonic conductivity and electrochemical performance at low I/C ratios. The effective diffusivity in the CL also decreases when the ionomer distribution is changed from uniform to non-uniform.
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- Graduation date
- Fall 2019
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.