Thermodynamic stability of gadolinia-doped ceria thin film electrolytes for micro-solid oxide fuel cells

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.