Influence of alumina dopant on the properties of yttria-stabilized zirconia for SOFC applications

The most important component of the solid oxide fuel cell (SOFC) is the dense electrolyte. Besides gastightness it must fulfill the requirements of good ionic conductivity and stability in reducing and oxidizing atmospheres. For this application yttria-stabilized zirconia is widely used. In this paper the effect of calcination temperature and milling time for zirconia powder stabilized with 8 mol% yttria (8YSZ) on the gastightness of the electrolyte layer was investigated. The influence of the addition of 0.77, 2 and 4 wt% Al2O3 to 8YSZ powder on the tightness and the sinterability of the electrolyte layer was studied. The performance of the cell with the electrolyte doped with 0.77 wt% Al2O3 was also investigated. The experiments show that the electrolyte layer, which was fabricated from 8YSZ powder (calcined at 1200°C) with particle size distributions of 0.25 μm–<0.3 μm (d50), gives the lowest leak rate. The Al2O3 added to 8YSZ improved the electrolyte tightness by increasing the sinterability of the electrolyte layer and reducing the sintering time. The performance of a cell with Al2O3 added to the electrolyte is better than that of a cell with an electrolyte of pure 8YSZ, especially at operating temperatures between 800 and 900°C.