چكيده به لاتين
Due to the importance of solid oxide fuel cell (SOFC) electrolyte on its performance and operating temperature, using modern methods to reduce costs and improve electrolyte properties, has always been of interest to researchers. In this research, the flash sintering method is used to produce the bilayer electrolyte (yttria-stabilized zirconia (YSZ) - gadolinia doped ceria (GDC)) because of its ability to sinter materials at low temperatures and very short times. The effect of process parameters on electrolyte properties has been studied.
Green YSZ tape was fabricated by tape casting method and coated by GDC using wet spray method. Response surface methodology was used to determine the experiment's situation and to interpretation the data. The relative density was measured by the Archimedes method. Structural, microstructural, chemical analysis, and electrical properties were studied by XRD, SEM, EDX, and EIS methods, respectively. Captured movies were used for shrinkage and incubation time calculations. SOFC performance was measured by a fuel cell testing system by the stepwise electrical load.
Results show that increasing current density leads to an increment of relative density. Flash sintered samples with LSM contact paste reach to higher density relative to samples flash sintered with Pt paste. A critical electric field strength (80V/cm) was needed to flash happening. Increasing electric field strength shortens the incubation time but does not affect sample density. A cubic to tetragonal transformation was detected at electric field strength higher than 300V/cm. By using EIS it revealed that higher oxygen vacancy in the grain boundary is responsible for improved ionic conduction in flash sintered samples. A starting mechanism for flash phenomena was suggested according to observation such as the higher critical field strength at reducing atmosphere and impossibility of flash without using contact paste. In the suggested mechanism, the oxygen molecule at ambient atmosphere reacts with oxygen vacancy and oxygen ion in the lattice. Also, we found that the effect of electric field in enhancing the diffuson of Zr and Ce cations is graetter than the temperature. By controlling the process parameter it is possible to reduce interdiffusion layer thickness. Flash sintering of YSZ/GDC dual-layer (T=800°С, E=80V/cm, J=200mA/mm2) reduced interdiffusion layer thickness to 1 μm. The thickness was 20 μm for conventionally sintered one (1450°С for 4 hours). The power density of SOFC based on flash sintered electrolyte was 300mW/cm2, which is about 15% higher than conventionally sintered one.
