SPUTTER-DEPOSITED MEDIUM-TEMPERATURE SOLID OXIDE FUEL-CELLS WITH MULTILAYER ELECTROLYTES

The deposition, interfacial impedances, and characteristics of solid oxide fuel cells (SOFC) with thin-film multi-layer electrolytes are described. The cell layers - a 1 mum thick Ag-YSZ cermet cathode, a 15 to 20 mum thick electrolyte, and a 1 to 2.5 mum thick Ni-YSZ anode - were deposited on porous alumina by reactive magnetron co-sputtering of metal targets in Ar-O2 mixtures. The effect of adding Y-stabilized Bi2O3 (YSB) and Y-doped CeO2 (YDC) layers at the yttria-stabilized-zirconia (YSZ) electrolyte surfaces was investigated. The open circuit voltage of the H2/H2O (3%), Ni-YSZ/electrolyte/Ag-YSZ, air fuel cells tested at 750-degrees-C was 0.78-0.85 V, less than expected theoretically, indicating some porosity in the electrolyte layers. The cell resistance was 4.5 OMEGA cm2 for a YSZ electrolyte, due mainly to the electrode interfacial resistances, and the maximum power density was 35 mW/cm2. Adding a 60 nm-thick YSB layer at the YSZ/Ag-YSZ interface reduced the air electrode resistance from almost-equal-to 1.4 to 0.45 OMEGA cm2, leading to an increase in the maximum power density to almost-equal-to 50 mW/cm2. Adding a 100 nm-thick YDC layer at the Ni-YSZ/YSZ interface further increased the maximum power density to 110 MW/CM2 at a cell resistance of 1.6 OMEGA CM2 . The three-layer YSB/YSZ/YDC electrolyte thus resulted in a factor-of-three increase in power density over a YSZ electrolyte.