Mechanisms of Protonic Surface Transport in Porous Oxides: Example of YSZ

The electrical properties and the charge carrier mechanism of porous 8 mol % yttria-stabilized zirconia (8YSZ) ceramic samples have been investigated over wide ranges of relative -humidity (RH); and temperature (25-400 degrees C). The presence pf humidity introduces protonic surface Conduction, and porous YSZ shhws pure protonic conduction below similar to 150 degrees C. H/D isotope effect studies combined with transport number measurements reveal a change in transport mechanism from structural diffilsion (Grotthuss type) to vehicular transport when the relative humidity exceeds similar to 60% RH, coinciding with a. changein the adsorbed water-layer from an ice-like to a water-like structure. Similarly, the activation energy for proton transport decreases from 0.43 to 0.28 eV when the relative humidity increases from 20% RH to 84% RH, reflecting changes in the enthalpies of armation and migration of charged species with increasing water layer thickness.