Abstract
Alternative energetic systems of the new generation conceptually differ from conventional energy systems, and among them one of the most perspective technologies is the technology of solid oxide fuel cells (SOFCs). Based on their characteristics SOFC are considered third-generation devices and occupy a leading position compared to the other fuel cell types. One of the most important components of the SOFC from an operational aspect is the solid electrolyte and its characteristics. Today, as the electrolyte for SOFC, cerium-oxide (CeO2) doped with rare earth ions is increasingly used due to better properties at lower temperatures in the range of 500-700 °C, which is the working temperatures for intermediate temperature solid oxide fuel cells (IT-SOFC). As an example application of CeO2 as solid electrolyte, in this paper the three different oxides in the form of solid solutions doped ceria (Ce0.80 Re0.20 O2-δ; Re= Yb3+, Y3+, Sm3+) were successfully synthesized by using self-propagating reaction at room temperature (SPRT method). This method was enabled to obtain very precisely, the targeted stoichiometry of the final products. The influence of different sized ionic radius on the properties synthesized nanopowders was investigated by using XRDP, Raman spectroscopy and TEM methods. According to XRPD and Raman spectroscopy results, single phase solid solutions of the fluorite structure were evidenced regardless of the type of dopants. Nanometric dimensions of the crystallites of the synthetized powders were confirmed by XRPD and TEM methods. A part of the obtained powdery samples was densified in ambiental air for 2 h at 1,550 °C. The sintering process did not lead to loss of the mole fraction (20%) of dopants in final compositions. Techniques such as XRPD, SEM and electrochemical impedance spectroscopy (EIS) were used for microstructural and electrical characterization of the sintered samples. The highest electrical conductivity (2.19 × 10−2 Ω−1 cm−1) was found for the sample with the composition Ce0.80 Y0.20 O2-δ, at 700 °C. For the intermediate temperature range, the value of conductivity activation energy for this sample was 0.28 eV. The results of electrical conductivity and high thermal stability for solid electrolytes based on rare earth doped CeO2 promote this type of material as a good candidate for application in IT-SOFC.
