Investigating the physico-chemical and electrochemical properties of various aliovalent cations doped ceria powders for electrolytic applications in solid oxide fuel cells

Abstract

Solid oxide fuel cells (SOFCs) are one of the most efficient energy conversion devices, yet their high operating temperatures have caused a bottleneck towards their commercialization. Due to sufficient conductivity and stability below 600 °C, doped ceria is under investigation for electrolytic applications in SOFCs. During this study, starting with Ce0.8Sm0.2O2-δ, 5% of Sm3+ was replaced by dopants of varying valencies and sizes giving Ce0.8Sm0.15X0.05O2-δ (where X = Bi3+, Mg2+, Li+), thereby aiming to keep the total dopant concentration constant. The structure-property relationship was studied using a number of techniques including XRD, Raman spectroscopy, FTIR spectroscopy and temperature dependent EIS. XRD indicated the presence of a minor phase belonging to MgO for the Mg2+ co-doped sample. Raman spectroscopy showed the presence of δ-Bi2O3 for Bi3+ doped SDC. Based on the quantitative analysis of Raman data we concluded that the materials were multi-phasic and co-dopants addition did not have a noticeable influence especially on defect concentration. In EIS data, measured from of 550–750 °C, change in conductance behavior was shown by Arrhenius plots for SCB and SCM when the test temperature was raised over 650 °C, possibly reflecting the combined conduction due to the additional phases along with SDC for these samples. Poor solubility of the non-rare earth metal ions into the ceria lattice was observed. This study suggests the need of a comprehensive analysis of doping mechanism preferably by synchrotron-based techniques to effectively incorporate low-cost non-rare earth metals into ceria lattice.