In this study, the effects of electrode microstructure and electrolyte parameters on intermediate temperature solid oxide fuel cell (ITSOFC) performance were investigated using a one-dimensional SOFC model from the Pacific Northwest National Laboratory (PNNL). After a brief review of the fundamental SOFC operating processes and a literature review incorporating more advanced SOFC topics, such as electrode microstructure modeling and mixed ionic and electronic (MIEC) composite cathodes, it was determined from the PNNL benchmark results that the dominating ITSOFC losses were caused from the activation and Ohmic overpotentials. The activation overpotential was investigated through the exchange current density term, which is dependent on the cathode activation energy, the cathode porosity, and the pore size and grain size at the cathode triple phase boundary (TPB). The cathode pore size, grain size, and porosity were not integrated in the PNNL model, therefore, an analytical solution for exchange current density from Deng and Petric (2005) was utilized to optimize their effects on performance. The Ohmic loss was determined to be entirely dependent on the electrolyte ionic conductivity, and an optimal value for this conductivity was determined. Simultaneous optimization of the above parametric evaluations led to a 388 % increase in performance from the PNNL benchmark case at 600 °C. Although this was deemed successful for this project, future research should be focused on numerically quantifying and modeling the electrode microstructure in two and·three-dimensions for more accurate results, as the electrode microstructure may be highly multi-dimensional in nature.

<p dir="ltr">Catalyzing a green hydrogen economy can accelerate progress towards achieving the goal of a sustainable energy map with net-zero carbon emissions by rapid strides. An environmentally benign electrochemical energy conversion system is the Polymer Electrolyte Fuel Cell (PEFC) which uses hydrogen as a fuel to produce electricity and is notably used in a variety of markets such as industries, commercial setups, and across the transportation sector, and is gaining prominence for use in heavy-duty vehicles such as buses and trucks. Despite its potential, the commercialization of PEFCs needs to address several challenges which are manifested in the form of mass transport limitations and deleterious mechanisms at the interfacial scale under severe operating conditions. Achieving a robust electrochemical performance in this context is predicated on desired interactions at the triple-phase boundary of the electrochemical engine of the PEFC – the porous cathode catalyst layer (CCL) where the principal oxygen reduction reaction (ORR) takes place. The liquid water produced as a byproduct of the ORR helps minimize membrane dehydration; however, excess water renders the reaction sites inactive causing reactant starvation. In addition, the oxidation of the carbonaceous support in the electrode and loss of valuable electrochemically active surface area (ECSA) pose major barriers that need to be overcome to ameliorate the life expectancy of the PEFC.</p><p dir="ltr">In this thesis, the multimodal physicochemical interactions occurring inside the catalyst layer are investigated through a synergistic blend of visualization and computational techniques. The spatiotemporal dynamics of capillary force-driven liquid transport that ensues concentration polarization thereby affecting the desired response will be probed in detail. The drop in efficacy of the ORR due to competing catalyst aging mechanisms and the impact of degradation stressors on chemical potential-induced instability will be examined. The reaction-transport-mechanics interplay in core-shell nanoparticles, a robust class of electrocatalysts that promises better mass activity compared to the single metal counterparts is further highlighted. Finally, the influence of electrode microstructural attributes on the electrochemical performance of the reverse mode of fuel cell operation, i.e., Proton Exchange Membrane Water Electrolyzers (PEMWEs) is investigated through a mesoscale lens.</p>