Development of Neodymium Doped Ceria Based Electrolytes for Applications in Intermediate Temperature Solid Oxide Fuel Cells (SOFCs)

Abstract

Solid oxide fuel cells (SOFCs) are currently attracting tremendous interest because of their huge potential in stationary heat and power generation. Currently SOFCs utilize Yttria stabilized zirconia as electrolyte material that works efficiently from 800-1000°C. The major current impediment of commercializing SOFCs is their high cost that results from high operating temperature. The need at this stage is to develop such materials that can offer better ionic conductivity at low temperature. Pure Ceria is poor ionic conductor but its conduction properties can be greatly enhanced by doping it with some trivalent rare earth atom such as Neodymium (Nd). In literature, there is not enough data available for Neodymium doped Ceria (NDC) electrolytes that can be a substitute for YSZ as they provide higher ionic conductivity at low temperatures. In this dissertation, two compositions Ce0.80Nd0.20O1.90 (NDC20) and Ce0.75Nd0.25O1.875 (NDC25) were initially selected to investigate the structural and electrical properties of Neodymium doped ceria electrolyte using sol-gel route. X-ray diffraction (XRD) and scanning electron microscope (SEM) results showed that powder particles containing cubic fluorite structure with homogenous and spherical shape with an average size of 1.1 μm were formed at pH10. DC electrical conductivity values for NDC25 and NDC20 were found to be 7.9x10-5 S/cm and 3.67x10-5 S/cm respectively at 650°C. We further enquired the effect of small amount of Sm, Y and K2CO3 to improve the conduction mechanism in NDC25. Conductivity of NDC25 greatly improved by adding small amount of Sm with composition of Ce0.75Sm0.15Nd0.10O1.875 (SNDC) and Y with composition of Ce0.75Y0.15Nd0.10O1.875 (YNDC) at 700°C . It was also depicted that Sm and Nd are best co-dopants for Ceria. K2CO3 was added into NDC25 with 10 and 20% by volume. It was observed carbonates greatly increased the conductivity values of NDC25 from 7.9x10-5 S/cm to 1.03x10-3 S/cm. The sequence in the conductivity values at 700°C found to be KNDC20>KNDC10>SNDC>YNDC>NDC25>NDC20.