Synergistic effect of manganese co-doping on densification, mechanical integrity and ionic conductivity of samarium-doped ceria electrolytes for intermediate-temperature solid oxide fuel cell applications

Abstract

In intermediate-temperature solid oxide fuel cells (IT-SOFCs), samarium-doped ceria (SDC) is one of the promising electrolytes due to its ability to provide high oxygen-ion conductivity and chemical stability. In this study, SDC electrolyte co-doping with manganese with three concentrations, 1%, 5%, and 10%, was synthesized with a solid-state reaction method and sintered at 1450°C without any calcination process. X-ray diffraction, densification, shrinkage, hardness, and ionic conductivity were done on manganese co-doped SDC electrolyte. X-ray diffraction (XRD) analysis confirmed that all compositions are in tetragonal fluorite structure formation. Co-doping manganese on SDC significantly enhanced the shrinkage from SDC 11.82% to 1Mn-SDC 21.52%. However, this experiment found that shrinkage was not directly correlated with densification; 10Mn-SDC exhibits 16.94% shrinkage and 90.54% relative density, while the optimum composition 1Mn-SDC exhibits 21.52% shrinkage and 90.18% relative density. The optimum composition, 1Mn-SDC, exhibits the highest Vickers hardness of 701.3 HV compared with 402.0 HV for undoped SDC. Impedance spectroscopy shows the conductivity improvement: at 300°C, 1Mn-SDC achieved 9.97  10^–2 S/cm compared to SDC, which showed a value of 7.1  10^–4 S/cm. Meanwhile, 800°C 1Mn-SDC reached 25.14 S/cm, outperforming SDC, which achieved 7.28 S/cm. On energy activation, it decreases from 1.27 eV to 0.79 eV, which indicates a lower energy barrier for conduction. These studies demonstrate that co-doping manganese on SDC significantly enhances the mechanical and electrochemical performance of SDC electrolytes, with 1Mn-SDC providing the most balanced combination of hardness and ionic conductivity for IT-SOFC applications.