An experimental investigation into micro-fabricated solid oxide fuel cells with ultra-thin La_0.6Sr_0.4Co_0.8Fe_0.2O₃ cathodes and yttria-doped zirconia electrolyte films

Thin-film solid oxide fuel cells (SOFCs) were fabricated with both Pt and mixed conducting oxide cathodes using sputtering, lithography, and etching. Each device consists of a 75-150 nm thick yttria-stabilized zirconia (YSZ) electrolyte, a 40-80 nm porous Pt anode, and a cathode of either 15-150 nm dense La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δ (LSCF) or 130 nm porous Pt. Maximum powers produced by the cells are found to increase with temperature with activation energies of 0.94-1.09 eV. At 500 °C, power densities of 90 and 60 mW cm^-2 are observed with Pt and LSCF cathodes, respectively, although in some conditions LSCF outperforms Pt. Several device types were fabricated to systematically investigate electrical properties of components of these fuel cells. Micro-fabricated YSZ structures contacted on opposite edges by Pt electrodes were used to study temperature-dependent in-plane conductivity of YSZ as a function of lateral size and top and bottom interfaces. Si/Si₃N₄/Pt and Si/Si₃N₄/Au capacitor structures are fabricated and found to explain certain features observed in impedance spectra of in-plane and fuel cell devices containing silicon nitride layers. The results are of relevance to micro-scale energy conversion devices for portable applications.