Fracture toughness and strength distribution at room temperature of zirconia tapes used for electrolyte supported solid oxide fuel cells

Abstract

Zirconia tapes are established for the application as electrolytes in solid oxide fuel cells. One of their functional tasks is to provide the structural integrity of the cell. The mechanical failure of the electrolyte would cause leakage between the electrodes, leading to a reduction of the performance of a whole fuel cell stack. In order to assess the reliability of a certain zirconia tape with respect to a specific stress distribution and environment, the strength has to be properly characterised. In the present study a selection of several commercial highly ionic conductive scandia doped zirconia tapes was investigated regarding their strength under inert and humid conditions at room temperature, which required the determination of the elastic constants and the fracture toughness as well.The strength of the different zirconia tapes ranks according to their fracture toughness, while the strength distributions typically exhibit a Weibull modulus of m = 10. It was found that all tapes suffer from sub critical crack growth, which leads to a limited lifetime at a given static load and a drastic reduction of the room temperature strength at time scales relevant for actual operation.