Influence of transition or lanthanide metal doping on the properties of Sr0.6Ba0.4Ce0.9M0.1O3-δ (M = In, Pr or Ga) electrolytes for proton-conducting solid oxide fuel cells

Proton-conducting electrolytes offer an alternative electrolyte to replace the oxygen-ion conducting conventional electrolyte for solid oxide fuel cells (SOFCs). In this study, proton-conducting Sr0.6Ba0.4Ce0.9M0.1O3-8 (M = In, Pr, Ga) electrolytes without Zr were synthesized by the glycine-nitrate process for intermediate-temperature SOFC applications. The thermal decomposition and crystalline structure of the electrolyte powders were analysed by thermogravimetry (TG) analyses and X-ray diffraction (XRD), respectively. The morphological structure and chemical stability of the electrolyte pellets were examined by field-emission scanning electron microscopy (FESEM) and XRD. Electrochemical impedance spectroscopy (EIS) analysis was used to evaluate the proton conductivity of each electrolyte pellet at different operating temperatures (500-800 degrees C) in a gas mixture composed of hydrogen (10%) and nitrogen (90%) humidified at room temperature (wet H2/N2), air humidified at room temperature (wet air) and dry air. The ideal calcination temperature for the electrolyte is determined to be 1000 degrees C based on TGA and XRD analyses, which indicate a high degree of crystallization without any formation of secondary phases. Furthermore, the relative density of all sintered electrolyte pellets is found to lie within an acceptable range (>90%) for good ion conduction. The Sr0.6Ba0.4Ce0.9Ga0.1O3-8 electrolyte displays the highest relative density (99%). However, the chemical stability analysis shows that Sr0.6Ba0.4Ce0.9Pr0.1O3-8 is the most stable electrolyte with a small additional secondary phase. The EIS results indicate that the Sr0.6Ba0.4Ce0.9In0.1O3-8 electrolyte shows the highest ionic conductivities of 1.80 x 10-3, 2.26 x 10-3 and 1.28 x 10-3 S/cm at 700 degrees C in wet H2/N2, wet air and dry air, respectively. Overall, Sr0.6Ba0.4Ce0.9M0.1O3-8 doped with transition elements (In and Ga) are considered potential electrolytes for proton-conducting SOFCs. In terms of sinterability, chemical stability and proton conductivity, the Sr0.6Ba0.4Ce0.9In0.1O3-8 electrolyte doped with indium (In) is considered the best electrolyte in this work.

Automated summary

Proton-conducting Sr0.6Ba0.4Ce0.9M0.1O3-8 (M = In, Pr, Ga) electrolytes without Zr were synthesized using the glycine-nitrate process for intermediate-temperature solid oxide fuel cell (SOFC) applications. The electrolyte powders were analyzed for thermal decomposition and crystalline structure. The morphological structure, chemical stability, and proton conductivity of the electrolyte pellets were examined. It was determined that Sr0.6Ba0.4Ce0.9In0.1O3-8 is the best electrolyte in terms of sinterability, chemical stability, and proton conductivity.