| Improving Plasma Sprayed YSZ Coatings for SOFC Electrolytes | ||
| Dr. Asif A. Syed1, Mr. Hannes Weckmann2, Ms. Zeynep Ilhan1, Dr. Johannes Arnold1 and Dr. Günter Schiller1, 1ITT, German Aerospace Center (DLR), Pfaffenwaldring 38 – 40, Stuttgart, 70569, Germany, 2BMW, Pfaffenwaldring 38 – 40, Stuttgart, 70569, Germany Yttrium- fully stabilized Zirconia (YSZ-FSZ), is the most widely used electrolyte material in high temperature SOFCs. The recent attempts directed towards reducing operating temperature of YSZ-based SOFCs were accompanied with decreased electrolyte thickness in order to compensate for higher ohmic losses at lower temperatures. Thinner electrolyte, however, leads to inferior leak tightness of theses layers, which consequently causes lower open circuit voltage (OCV) and thus lower power densities of SOFC. This issue is of primary concern in plasma sprayed YSZ electrolytes.
The present work investigates the influence of feedstock powder and plasma forming gases on the leak tightness of vacuum plasma sprayed YSZ deposits. The two selected feedstock powders were commercially available fused and crushed YSZ, stabilized with 8 or 9.5 mole % Y2O3, having a very similar particle size range (-22+5 µm). Both powders were sprayed with a torch consisting Mach 3 deLaval anode nozzle on porous FeCrMnTi alloy substrates at 8 kPa chamber pressure. A D-optimal Design of Experiments was developed to study the influence of three plasma forming gases (Ar, He and H2) on deposition efficiency of powders and the leak rates of the coatings. Better deposition efficiency of YSZ powders was achieved principally by spraying with higher plasma enthalpy whereas plasma gas mass flow rates exercised minor effect. Deposit leak tightness was predominantly influenced by plasma gas mass flow rates and plasma enthalpy had little measurable effect. These results suggested that higher particle velocity is the major criteria for improving deposit leak tightness whereas particle temperature controls their deposition efficiency. Online particle diagnostics were employed to verify these results.
Electrochemical testing of SOFCs, consisting of similar VPS NiO+YSZ anode and different YSZ electrolyte deposits, were performed to conclude the influence of leak tightness and microstructure of electrolyte deposit on cell behavior. | ||