The thickness dependence of oxygen permeability in sol-gel derived Ce _o.8Gd_O.2O_2-δ-CoFe₂O ₄ thin films on porous ceramic substrates: A sputtered "Blocking" Layer for thickness control

Mixed conductive oxides are a topic of interest for applications in oxygen separation membranes as well as use in producing hydrogen fuel through the partial oxidation of methane. The oxygen flux through the membranes is governed both by the oxygen ionic conductivity as well as the material's electronic conductivity; composite membranes like Ce_o.8Gd_O.2O _2-δ (CGO)-CoFe₂O₄ (CFO) use gadolinium doped ceria oxides as the ionic conducting material combined with cobalt iron spinel which serves as the electronic conductor. In this study we employ 50 nm sputtered CeO₂ layers on the surface of porous CGO ceramic substrates which serve as solution "blocking" layers during the thin film fabrication process facilitating the control of film thickness. Films with thickness of - 2 and 4 microns were prepared by depositing 40 and 95 separate sol-gel layers respectively. Oxygen flux measurements indicated that the permeation increased with decreasing membrane thickness; thin film membrane with thickness on the micron level showed flux values an order of magnitude greater (0.03 mol1cm₂ s) at 800°C as compared to 1mm thick bulk ceramic membranes (0.003 imolIcm₂).