REDUCTION OF THERMAL EXPANSION IN YTTRIA-STABILIZED ZIRCONIA (YSZ) SOLID OXIDE FUEL CELL (SOFC) ELECTROLYTE BY TUNGSTEN ADDITION

The current research is focused on tungsten addition to YSZ solid electrolyte in the initial synthesis and its effect on the properties and performance of the fuel cell. Zirconium tungstate is known for having a negative thermal expansion whereas YSZ expands considerably with temperature. Lower thermal expansion in the electrolyte may result in better compatibility to perovskite-type cathodes and a shorter starting time. Cubic YSZ with 20 at.% Y and 1 at.% W was synthesized using the sol-gel method, from yttrium nitrate hexahydrate, zirconium oxynitrate hydrate and tungstic acid dissolved in ethanol. The resulting powder was heat treated at 400-1200 °C for 2 hours to achieve crystallinity. It was found that the best crystallinity was achieved at 1200 °C. XRD results show a single cubic phase after the powder was air quenched. In addition, the thermal diffusivity was determined using Laser Flash Analysis (LFA), and the thermal expansion using Thermomechanical analysis (TMA).