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Abstract: We report on single phase polycrystalline Ba0.5Sr0.5Co0.8Fe0.2O3 thin films grown on (100) (Y2O3)0.08(ZrO2)0.92 substrates by radio frequency sputtering. Detailed studies on electrical conductivity as a function of temperature up to 500°C are carried out for films in the 20–100nm thickness range. Free-standing thin film micro-solid oxide fuel cells utilizing nanostructured Ba0.5Sr0.5Co0.8Fe0.2O3 cathodes are fabricated and tested for the first time. A maximum power density of 35mWcm−2 at 520°C was obtained with Ba0.5Sr0.5Co0.8Fe0.2O3/(Y2O3)0.08(ZrO2)0.92/Pt micro-solid oxide fuel cells. These results indicate the significance of microstructure on electrical properties of Ba0.5Sr0.5Co0.8Fe0.2O3 and present the first successful thin film micro-solid oxide fuel cells integrating Ba0.5Sr0.5Co0.8Fe0.2O3. We anticipate these results to be of relevance in advancing micro-solid oxide fuel cells for reduced temperature operation with dense oxide cathodes. [Copyright &y& Elsevier]

Abstract: Functional all-oxide thin film micro-solid oxide fuel cells (μSOFCs) that are free of platinum (Pt) are discussed in this report. The μSOFCs, with widths of 160μm, consist of thin film La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) as both the anode and cathode and Y0.08Zr0.92O1.96 (YSZ) as the electrolyte. Open circuit voltage and peak power density at 545°C are 0.18V and 210μWcm−2, respectively. The LSCF anodes show good lattice and microstructure stability and do not form reaction products with YSZ. The all-oxide μSOFCs endure long-term stability testing at 500°C for over 100h, as manifested by stable membrane morphology and crack-free microstructure. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of high performance nanostructured oxide electrodes is critical to advancement of energy technologies such as intermediate temperature solid oxide fuel cells. In this communication, we demonstrate that photo-excitation during crystallization of nanostructured 60-nm-thick La0.6Sr0.4Co0.8Fe0.2O3−δ films leads to a significant improvement in electrical conductivity. Crystallization kinetics is also enhanced by photo-excitation while the crystallization onset temperature remains similar. [Copyright &y& Elsevier]

Abstract: Dense ultra-thin nanocrystalline La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) films with thickness of ∼50nm, have been sputtered on nanoporous anodic alumina-supported nanocrystalline thin film yttria-stabilized zirconia and patterned by photolithography into microelectrodes. This approach enables low-temperature (425–550°C) electrochemical properties of dense ultra-thin nanocrystalline LSCF to be characterized. The results reveal that the electrochemical resistance of nanocrystalline ultra-thin LSCF is dominated by the oxygen surface exchange reaction at the electrode surface with an activation energy of 1.1eV. Area-specific resistance of LSCF was obtained and the results are of potential relevance to utilizing nanostructured oxide cathodes for micro-SOFCs operated at low temperatures. [Copyright &y& Elsevier]

Abstract: 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 75–150nm thick yttria-stabilized zirconia (YSZ) electrolyte, a 40–80nm porous Pt anode, and a cathode of either 15–150nm dense La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF) or 130nm porous Pt. Maximum powers produced by the cells are found to increase with temperature with activation energies of 0.94–1.09eV. At 500°C, power densities of 90 and 60mWcm−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. [Copyright &y& Elsevier]

Abstract: Nanocrystalline lanthanum strontium cobalt ferrite (LSCF) ultra-thin films with high in-plane electrical conductivity have been deposited by RF sputtering from composite targets. The films, with nominal thickness of 54nm, are crystalline when annealed or deposited at temperatures above 450°C. Effects of annealing temperature, annealing time, and substrate temperature on crystallization, microstructure, and room temperature lateral electrical conductivity have been systematically studied. No interfacial reaction products between the LSCF and single crystalline yttria-stabilized zirconia (YSZ) were observed from X-ray diffraction studies upon annealing until 750°C. In-plane electrical conductivity as high as 580Scm−1 at 650°C has been observed for LSCF thin films deposited on single crystalline YSZ substrates and sputtered nanocrystalline YSZ thin films; while activation energy for conductivity were determined to be 0.15eV and 0.10eV for the former and latter films, respectively, in 650–400°C range. The high in-plane electrical conductivity for the nanocrystalline LSCF ultra-thin films is likely attributed to their low level of porosity. Micro-solid oxide fuels cells using 15nm thick LSCF films as cathodes and sub-100nm yttria-doped zirconia thin film electrolytes have been fabricated successfully and demonstrated to achieve peak power density of 60mWcm−2 at 500°C. Our results demonstrate that RF sputtering provides a low-temperature synthesis route for realizing ultra-thin nanocrystalline LSCF films as cathodes for intermediate- or low-temperature solid oxide fuel cells. [Copyright &y& Elsevier]