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Focusing on the application of carbon slurry electrodes in advanced electrochemical power and energy storage systems, the electrical conductivity of such electrodes is thoroughly investigated experimentally. A slurry electrode made from steam-activated Norit is analyzed to estimate its electronic and ionic conductivities separately. A single-pass rectangular flow channel with three different widths of 4.1, 3.6, and 3.1 cm is used to investigate the effect of the flow channel geometry on slurry electrode conductivity. Three different slurry concentrations of 5, 10, and 15 wt % are investigated, while electronic and ionic conductivities are separately measured using distilled water and sulfuric acid as electrolytes. The charge conduction improvement due to the availability of more charge-carrying particles in the slurry is quantified, and it is shown that up to about 220 and 120% increase in electronic conductivities can be achieved by increasing carbon loading from 5 to 10 and 15 wt %, respectively. Analysis of slurry conductivity variations from a static condition to a flow rate of 280 mL min–1 with different channel widths and concentrations shows that the slurry conductivity reaches a maximum value at an intermediate flow rate and is then gradually decreased. The optimum working condition of a slurry electrode is finally discussed.

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The impedance characteristics of proton exchange membrane (PEM) fuel cells are studied and analyzed in this thesis. The modeling approaches presented in literature are thoroughly reviewed and categorized as the measurement-modeling and process-modeling approaches. In the former category, a hypothetical equivalent circuit which has the impedance characteristics similar to measured impedances is presented. Since the equivalent circuit is not directly resulted from the physical and chemical properties of the PEM fuel cells, the majority of the measurementmodeling approaches lead to dubious conclusions. In the process-modeling approach, on the other hand, the governing equations of the fuel cell must analytically be solved to determine and the impedance. However, a few process-modeling approaches presented in literature have shown to be indirectly based on the same assumptions as the measurement-modeling approach, and hence, those can also lead to similar conclusions. Therefore, these process-modeling approaches are referred to as the semi-process models here.In this thesis, the first complete process model for PEM fuel cells is presented which is not based on the above-mentioned assumptions. For each source of the losses in the fuel cell (i.e., the ohmic, activation and concentration overpotentials), a process model and equivalent circuit are obtained and compared against the impedance measurements reported in literature. The complete model (obtained by combining the models of the three losses) is then verified against the impedances measured in different operating conditions. Using the verified model, the measured Nyquist plots of the PEM fuel cells reported in literature are categorized. As a result, the dominant physical and chemical parameters controlling various arcs of the Nyquist plot are determined. Finally, the sensitivity analysis of the impedance characteristics of fuel cells is conducted using the verified model. As a result of this analysis, a minimum change in the operating conditions which results in statistically different Nyquist plots are determined.Finally, as an application of the model presented here, the impedance of the cell in the anode and cathode starvation modes are studied. It is shown that the anode starvation cannot be recognized from the impedance measurements, as predicted by the model. iii Preface This research was conducted in the Advanced Thermo-Fluidic Laboratory (ATFL) at University of British Columbia, Okanagan campus, under supervision of Dr. Mina Hoorfar. The results of this research have been published in several peer-reviewed journal articles and conference proceedings. Chapter 1 includes the discussions published as a review journal article (S.M. Rezaei Niya, M. Hoorfar (2013) 'Study of proton exchange membrane fuel cells using electrochemical impedance spectroscopy technique -A review ', Journal of Power Sources, Vol. 240, and also a journal article discussing the details of the process modeling approach (S.M. Rezaei Niya, M.Hoorfar (2015) 'Measurement, semi-process and pr...

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The paper presents an approach for estimating the permeability of a porous medium that is based on the characteristics of the porous structure. The pressure drop in different fluid flow passages is estimated and these are combined to evaluate the overall reduction. The theory employed is presented and the level of accuracy for different cases is discussed. The successive steps in the solution algorithm are described. The accuracy and computational efficiency of the approach are compared with results obtained from a finite-element-based multiphysics formulation. It is shown that for a comparable accuracy, the computational efficiency of the approach can be two orders of magnitude faster. Finally, the model predictions are examined with conventional relationships that have been reported in the literature and are based on permeability-porosity relationships. It is shown that estimating the permeability of a porous medium using porosity can lead to an order of magnitude error and the expected permeability range in different porosities is presented using 10 000 random structures.