Direct experimental comparison of YSZ electrolytes fabrication approaches: powder compression and slurry casting

Hydrogen related technologies have gained importance in the latest period due to the hydrogen role in the energy transition process from fossil to sustainable sources. Solid oxide cells (SOCs) represent one of the most promising technologies. Its basic unit comprises of an electrolyte, an anode and a cathode. Due to the high operation temperature (~ 800 °C) it does not need Pt-metals catalysts and features higher efficiency than lower temperature cells. However, the high operation temperature poses high requirements on the materials properties. Despite a significant material development, the electrolyte is still responsible for majority of ohmic losses in the system. An optimal electrolyte must be highly conductive and gas impermeable to achieve a high cell performance. Thus, the aim of this work of thesis is to fabricate the YSZ electrolyte with superior properties in a reproducible manner. Two different methods were used: powder compression and slurry casting, where the former is generally used for laboratory scale and the latter for industrial scale applications. The fabrication of electrolytes by powder compression was already optimized in previous works. Therefore, the properties of these electrolytes served as a reference benchmark. The main attention was, thus, paid to optimize the state-of-the-art fabrication method – the slurry casting. The morphology and electrochemical properties of fabricated electrolytes were analyzed in order to determine the impact of fabrication procedure conditions (e. g. sintering temperature and materials/slurry composition). Using both methods the electrolytes were successfully prepared. Despite a significant progress in the optimization of electrolyte preparation by slurry casting method, the gas impermeability was still compromised due to the remaining porosity within the samples. Thus, the sintering procedure needed to be optimized to ensure gas tightness. Yet, electrolytes fabricated by slurry casting method exhibited a significantly higher ohmic resistance compared to those prepared by powder compression. This thesis was developed in cooperation with the Department of Inorganic Technology of the University of Chemistry and Technology in Prague (UCTP), which made available its laboratories for the carrying out of the experimental process.