R Vasquez Cavieres’s research while affiliated with Swiss Federal Institute of Aquatic Science and Technology and other places

To increase power density at reduced temperature operation of SOFC, thin film 8YSZ electrolytes were deposited on Ni–YSZ anode support plates by tape casting and cofiring. Cathode behaviour, limiting cell output at lower temperature, was studied in more detail. Cathodes were deposited by screenprinting and firing. With consecutive layers of doped lanthanum manganite and cobaltite, power density of 0.5 W cm−2 at 750°C was obtained using hydrogen fuel. On cells of 100 cm2, no fuel diffusion limitation above 70% conversion occurred, and electrical efficiency of 35% was achieved. Actual cell temperature increases significantly above a current density of 0.3 A cm−2. This effect causes erroneous electrode and cell characteristics.

oarse 8YSZ powders destined for plasma spray deposition were obtained from three different suppliers (Hochrhein, Magnesium Elektron, Unitec). Their ionic conductivities were measured by impedance spectroscopy on pellets prepared by vacuum hot pressing. Density was adequate for one powder (Unitec, 95%) but poor for the other two (73-80%). For the latter samples, conductivity was a factor of 1.5 below reference values for pure dense 8YSZ, owing to their porosity. For the former samples, however, the conductivity was a factor > 3 below 8YSZ reference values. An additional resistance, responsible for this large discrepancy, appeared in the impedance response and is ascribed to the distinct microstructure at intergranular zones within these otherwise dense samples.