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.

This thesis deals with liquid aprotic electrolytes based on sulfolane with added flame retardant. The theoretical part of the thesis explains concepts - mainly aprotic electrolytes, flame retardants, and their practical use. It also discusses lithium - ion accumulators and materials used in them while focusing on the electrolyte function. The practical part of the thesis aims to measure the properties of aprotic electrolytes: their conductivity, potential window and flashpoint. It also contains a review of the measurement results.