Reactive Sputtering Deposition and Electrochemical Characterisation of Thin Solid Electrolyte Membranes for Solid Oxide Fuel Cells

Solid oxide fuel cells directly convert the chemical energy of a fuel into electricity. To enhance the efficiency of the fuel cells, the thickness of the gastight solid electrolyte membranes should be as thin as possible. Y2O3-stabilised ZrO2 (YSZ) electrolyte films were prepared by reactive sputtering deposition using Zr/Y targets in Ar/O-2 atmospheres. The films were 5 - 8 mu m thin and were deposited onto anode substrates made of a NiO/YSZ composite. After deposition of a cathode with the composition La0.65Sr0.35MnO3 the electrochemical properties of such a fuel cell were tested under operating conditions at temperatures between 600 degrees C and 850 degrees C. Current-voltage curves were recorded and impedance measurements were performed to calculate apparent activation energies from the fitted resistance data. The conductivity of the YSZ films varied between 4.6.10(-6) S/cm and 2.2.10(-5) S/cm at 400 degrees C and the fuel cell gave a reasonable power density of 0.4 W/cm(2) at 0.7 V and 790 degrees C using H-2 with 3 % H2O as fuel gas. The gas compositions were varied to distinguish the electrochemical processes of the anode and cathode in the impedance spectra.