Reducing effect of contaminants in solid oxide fuel cell electrolyte by spark plasma sintering

Spark plasma sintering (SPS) technology was adopted to reduce the detrimental effect of SiO₂ and Cr₂O₃ contaminants on 8 mol-% yttria stabilised zirconia (YSZ) electrolyte. Contamination of SiO₂ not only significantly reduces the ionic conductivity of the YSZ electrolyte, especially grain boundary conductivity, it also retards the densification process during sintering. Also, the addition of 0·5 wt-%Cr₂O₃, whilst marginally reducing grain boundary conductivity, can promote the densification process regardless of sintering technique adopted, be it conventional electrical resistance heating or SPS. The effects of SPS sintering conditions, such as sintering temperature, isothermal dwell time, applied uniaxial pressure and number of repeated SPS cycles on the relative density and ionic conductivity of the contaminated YSZ electrolytes were investigated in detail. The results showed that SPS sintering could alleviate the harmful effect of contaminants on grain boundary conductivity, with minimal effect on the grain interior conductivity. It can also sinter the YSZ electrolyte to near full density (about 98%) in around 3 min.