Revisiting Fe-doped 8YSZ as the electrolyte of SOFC – From sintering to electrochemical performance

Abstract

One of the main challenges in preparing a dense and ionic conductive yttria-stabilized zirconia (YSZ) solid electrolyte is its high sintering temperature. Iron has been suggested as an efficient additive for Yttria-stabilized Zirconia (YSZ) to reduce its sintering temperature with the least detrimental effect on ionic conductivity. In this study, a deeper exploration of the iron’s effect on the physical, microstructural, and electrical properties of YSZ was conducted. 8YSZ samples with different contents of Fe2O3 (0, 1, 3, 5, 7 mol%) were prepared by tape casting and sintered at 1200 °C and 1300 °C for 4 h. X-Ray diffraction (XRD) analysis, scanning electron microscopy (SEM), optical dilatometry, and electrochemical impedance spectroscopy (EIS) were performed. The results showed that iron does not affect the stability of the cubic phase structure. Estimating oxygen vacancy concentrations by EIS revealed that increasing Fe2O3 concentration resulted in decreamnet of oxygen vacancy concentrations at the space-charged layer and deteriorates the grain boundary conductivity. On the other hand, adding Fe2O3 led to grain growth and grain boundary length reduction which, as an opposite factor, reduced the destructive effect of grain boundary on conductivity. The maximum total ionic conductivity of 0.044 S/cm was achieved by adding 3 mol% of Fe2O3 to 8YSZ sintered at 1300 °C.