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 (Ce 0.8 Gd 0.2 O 1.9− 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 (Ce 0.8 Gd 0.2 O 1.9− 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 O 2− 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 Ce 0.8 Gd 0.2 O 1.9− 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.