| Abstract [eng] |
In large-scale energy conversion systems, hydrogen solid oxide fuel cells are gradually emerging as a promising technology that enables the highly efficient conversion of the chemical energy stored in hydrogen molecules into electricity, without releasing harmful byproducts into the environment. In order to reduce the high operating temperature of these fuel cells, cerium oxide, doped with rare earth elements (especially samarium and gadolinium), is being extensively studied. This ceramic material exhibits high oxygen ion conductivity at intermediate temperatures (500-700 °C) making it a strong candidate for electrolyte applications in fuel cells. This work examines in detail the physical properties of cerium oxide ceramics co-doped with samarium and gadolinium oxides. The literature review discusses the influence of dopant incorporation into the cerium oxide crystal lattice, the mechanisms of defect formation, and the factors that enhance or suppress ionic mobility at bulk and grain boundaries. The main methods of ceramic synthesis and their effect on the morphology and microstructure of the synthesized powders are reviewed. In addition, the importance of ceramic sintering and the influence of temperature on the crystalline structure and mechanical stability of the produced materials are highlighted. In order to investigate and compare the thermal, structural, morphological, and electrical properties of ceramics produced by different synthesis methods, a ceramic material with the stoichiometric formula Ce0.825Sm0.0875Gd0.0875O2-δ was prepared. Two chemical synthesis methods were selected for powder synthesis: the combustion method, which is fast and inexpensive, and the co-precipitation synthesis route, which is characterized by better uniformity of the synthesized particles. Thermal analysis of the resulting ceramic powders revealed that their behaviour during thermal treatment differs, indicating non-uniform decomposition processes occurring within the material. In both cases of ceramic synthesis, X-ray diffraction analysis confirmed a fluorite-type cubic structure but identified different mechanisms of crystal growth. Scanning electron microscopy studies showed that the synthesized powders have a similar structure: compact and homogeneous, differing only in the size of the formed grains. To investigate the electrical properties, the powders were compressed into dense, mechanically stable pellets. Impedance spectroscopy revealed that co-doping cerium oxide with samarium and gadolinium increases the ceramic’s bulk ionic conductivity, however, the overall conductivity is limited by the grain boundaries, which are strongly influenced by the choice of synthesis method. |
