Constrained and non-constrained sintering of plasma-sprayed zirconia based electrolytes for SOFCs

Kurzfassung

The current development in SOFCs is focused on reducing the operating temperature below 800°C. The reduced operating temperature promotes durability of cells and decreases stringent demands on peripheral components. However, with lower temperature the ionic conductivity of electrolytes decreases. Thickness reduction of the conventionally used yttria-stabilized zirconia electrolyte by using nanostructured particles as feedstock is a possibility to avoid this problem. Another possibility is the use of an electrolyte with improved ionic conductivity for intermediate temperature SOFCs, e.g. scandia-stabilized zirconia. Within this work zirconia based electrolyte layers were deposited on metal substrates using plasma spraying. As all thermal sprayed coatings contain some porosity, which influences the cell performance, the sprayed electrolyte layers were sintered in a second step. Plasma-sprayed coatings were under compressive stresses. In order to achieve a better understanding of differences in the sintering behaviour, plasma sprayed layers were sintered under constrained and non-constrained conditions in the temperature range of 800 to 1520 °C and characterised. Sintering properties, microstructure, and conductivity of sprayed and sintered electrolyte layers were investigated.