Sodium Doped Strontium Silicates as Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells

Abstract

Solid oxide fuel cells (SOFCs) are considered as important green energy devices for the 21st century due to its high chemical to electrical energy conversion efficiency, modular design and fuel flexibility. However, the widespread commercialization of SOFCs has not been realized due to its cost associated with cell fabrication, electrode/ electrolyte materials and its maintenance. The conventional electrolyte, Yttria-stabilized Zirconia requires high operating temperature (800 - 1000 0C) to achieve sufficient oxide-ion conductivity, which increases the cost and exacerbates the instability between the components [1]. Therefore, there is considerable interest in developing alternative electrolytes with oxide ion conductivity > 10−2 S/ cm at intermediate temperature (IT) (500 - 700 0C). Hence, here we successfully synthesized IT electrolytes Sr1−xNaxSiO3− d (x = 0.0, 0.45) by solid state reactions. XRD, Solid state NMR, FE-SEM/ EDS and impedance spectroscopy are used for the structural and electrical studies. From the XRD, it is evident that both the samples can be indexed in monoclinic c2/c space group (15) [2]. 29Si solid state NMR reveals a sharp single peak at −86 ppm for SrSiO3. Broadening of the peak at ~ −89 ppm indicates the presence of glassy Na2Si2O5 phase in Sr0.55Na0.45SiO3− d [3]. FE-SEM image of Sr0.55Na0.45SiO3− d clearly shows the amorphous Na2Si2O5 dispersed in SrSiO3 insulating crystalline phase. EDS analysis confirms that grain is Na-deficient (SrSiO3) and grain boundary (GB) is Na-rich phase (Na2Si2O5). The doping of Na into SrSiO3 leads to the formation and segregation of glassy Na2Si2O5 along the GBs, which is the main reason for high electrical conductivity. Among, Sr1−xNaxSiO3− d (x = 0.0, 0.45), SrSiO3 behaves as an insulator and Sr0.55Na0.45SiO3− d exhibits highest conductivity in the measured temperature range, which makes it as electrolyte for intermediate temperature SOFCs. Figure 1