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Next-generation micro-solid oxide fuel cells for portable devices require nanocrystalline thin-film electrolytes in order to allow fuel cell fabrication on chips at a low operation temperature and with high power outputs. In this study, nanocrystalline gadolinia-doped ceria (Ce0.8Gd0.2O1.9− x) thin-film electrolytes are fabricated and their electrical conductivity and thermodynamic stability are evaluated with respect to microstructure. Nanocrystalline gadolinia-doped ceria thin-film material (Ce0.8Gd0.2O1.9− x) exhibits a larger amount of defects due to strain in the film than state-of-the-art microcrystalline bulk material. This strain in the film decreases the ionic conductivity of this ionic O2− conductor. The thermodynamic stability of a nanocrystalline ceria solid solution with 65 nm grain size is reduced compared with microcrystalline material with 3–5 μm grain size. Nanocrystalline spray-pyrolyzed and PLD Ce0.8Gd0.2O1.9− x thin films with average grain sizes larger than 70 nm show predominantly ionic conductivity for temperatures lower than 700°C, which is high enough to be potentially used as electrolytes in low to intermediate-temperature micro-solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: The grain coarsening in dense nanocrystalline gadolinia-doped ceria (CGO) and CeO2 was studied for the grain size regime from 10 to 250nm. Dense ceria-based thin films were prepared by spray pyrolysis and pulsed laser deposition on sapphire substrates. The small grain-sized CGO and CeO2 microstructures were surprisingly stable and showed self-limited grain growth and relaxation of the microstrain with time. In this regime, material transport occurs via grain boundary diffusion leading to densification and grain coarsening in the thin films. A continuous transition to common grain growth kinetics was observed for larger grains at higher temperatures. [Copyright &y& Elsevier]

Abstract: Nickel oxide/Ce0.8Gd0.2O1.9− x (NiO/CGO) films were deposited by spray pyrolysis and pulsed laser deposition on polished CGO electrolyte pellets. The thicknesses of the as-deposited films were 500–800 nm. The sprayed films showed a homogeneously distributed nano-grain sized microstructure after annealing in air whereas the PLD films exhibited a texture with elongated columnar grains oriented perpendicular to the substrate surface. The electrochemical performance of the Ni/CGO cermet thin film anodes was measured in a symmetrical anode/electrolyte/anode configuration in a single gas atmosphere setup by impedance spectroscopy. The polarization resistance of 60/40 vol.% Ni/CGO spray pyrolysed films decreased with decreasing grain size and was 1.73 and 0.34 Ω·cm2 for grain sizes of 53 and 16 nm, respectively, at 600 °C in 3% humidified 1:4 H2:N2. The activation energy was 1.45 and 1.44 eV in the temperature range of 400–600 °C. The performance of the 49/51 vol.% Ni/CGO PLD cermet film was comparable to the spray pyrolysis films and was 0.68 Ω·cm2 at 600 °C with an activation energy of 1.46 eV. The electrochemical performance was similar to state-of-the-art thick film anodes and the Ni/CGO thin film cermets are promising candidates as electrodes in micro solid oxide fuel cells. [Copyright &y& Elsevier]