Gadolinium doped ceria nanostructured oxide for intermediate temperature solid oxide fuel cells

Highlights: • The ratio of chelating and polymeric agents has effect on the morphology and electrical properties of GDC electrolyte. • XRD data confirmed a single phase fluorite type structure. • Both total and grain boundary ionic conductivities increase as grain size becomes finer. • The oxygen ion conduction is controlled by grain boundary. -- Abstract: Effect of complexing agent/transition metal ratio (R = CA/TM; R = 1, 2, and 3) on microstructure, and physical and electrical properties of Gd_0.1Ce_0.9O_2-δ (GDC) powders synthesized by a polymeric route based on a modified sol-gel method, was studied. The samples were characterized by Termogravimetry (TG), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), dilatometry and impedance spectroscopy (IS). XRD and SEM-EDS analyses confirmed attainment of stoichiometric composition, and the formation of a single-phase fluorite-type structure at 800 °C. It was found that grain size increased upon increasing both temperature and R ratio, with measured average grain sizes of 0.9, 1.4, and 1.9 µm for GDC-R1, GDC-R2, and GDC-R3, respectively. A remarkable increase in specific surface area (A_BET) is observed in GDC-R1 (6.4 m²/g) in comparison with GDC-R2 (15.2 m²/g) and GDC-R3 (15.9 m²/g) powders. GDC-R1 sample sintered at 1400 °C presented the lowest values for average grain size. This sample also exhibited the highest ionic conductivity (σ_600°C=1.42 × 10⁻² S·cm⁻¹, σ_700°C=5.12 ×10⁻² S·cm⁻¹) and the lowest value for energy activation (Ea = 0.66 eV) in air.