High surface proton conduction of a-axis oriented CeO_2- thin film on (200) YSZ substrate

We have prepared a-axis oriented CeO2-delta thin films prepared on yttrium-stabilized zirconium (200) single crystal substrates by RF magnetron sputtering using a ceramic target. The amount of oxygen vacancies in the CeO2-delta thin films was quantitatively evaluated by X-ray absorption spectroscopy and defect chemical analysis. In terms of its electronic structure, the O 1s photoemission spectrum of the wet-annealed film shows an O-H bond peak, which suggests proton conduction. The a-axis oriented CeO2-delta thin film annealed at 600(degrees)C in a wet atmosphere exhibit high proton conductivity of more than 10(1) Scm(-1)K at medium temperature range from 300(degrees)C to 550(degrees)C by thermal activation process and surface proton conductivity of sigma T = similar to 7.0 x 10(-1) Scm(-1)K by Grotthuss mechanism below 50(degrees)C. The enhancements of proton conductivities are considered to be due to large amount of oxygen vacancies of similar to 3.3% at the surface of wet-annealed CeO2-delta thin film. These results indicate that the wet-annealed a-axis oriented CeO2-delta thin films can be applied as an electrolyte for solid oxide fuel cell operating at medium temperature range or electric double layer transistor operating below 50(degrees)C.