Structural, electrical and thermal studies on microwave sintered Dy and Pr co-doped ceria ceramics as electrolytes for intermediate temperature solid oxide fuel cells

Abstract

The present study was focused on the effects of co-doping on the conductivity enhancement of CeO2-based solid ceramics for application as electrolytes in intermediate temperature solid oxide fuel cells (IT-SOFCs) and the correlation of ionic conductivity variations with micro structural alterations resulting from the addition of co-dopants. Nano-crystalline Dy and Pr co-doped ceria Ce0.8Pr0.2−xDyxO2−δ solid solutions were successfully synthesized by sol–gel auto-combustion and innovative densification by energy efficient microwave sintering (MS) at 1300 °C. The XRD results in concurrence with Raman studies ascertained the formation of cubic fluorite structure in the entire range of composition. The lattice parameters obtained by Rietveld refinement showed lattice contraction with increased dysprosium content. MS has resulted in improved densification and the relative densities of all the samples were noticed above 96% of the theoretical density. TEM images confirmed the nano-crystalline character in the as-prepared samples with the particle sizes measured around 20 nm. SEM micrographs showed spherical faceted near-uniform grains (average grain sizes around 225 nm) with distinct grain boundaries and negligible porosity. Formation of oxygen vacancies and their concentration in all the samples was assessed with the help of Raman spectroscopy. Total ionic conductivity values and activation energies were measured depending on the Dy content. The ionic conductivity of the best composition was found to be 6.8 mS cm−1 at 500 °C. Thermal expansion co-efficient of the samples was matched with that of the commonly used electrode materials. These results gave rise to the firm conclusion that the investigated co-doped ceria has the potential to be utilized as an electrolyte for IT-SOFC applications.