Low temperature proton conduction in bulk nanometric TiO2 prepared by high-pressure field assisted sintering

We investigated the conductivity of high-density bulk-anatase samples with a grain size between 24 and 56 nm prepared by high pressure field-assisted sintering. When exposed to humid atmosphere, the insurgence of proton conductivity was observed for temperatures below 350 degrees C. Below this temperature, the samples showed a conductivity several orders of magnitude higher than that measured under dry oxygen atmosphere. The protonic conductivity strongly increased as grain size decreased, while a negligible dependence from porosity was observed when the latter ranged between 8 and 25 vol%. If compared with zirconia- and ceria-based nanomaterials with similar grain size, bulk nanometric anatase showed the highest low temperature protonic conductivity as well as the highest crossover temperature between dry and humid conduction behavior.