The behavior of SrCe0.95Th0.05O3 in various gases at high temperatures was investigated. In the case of air, O or N, the material exhibited a low electronic-hole conduction below 800C and an O ionic conduction above 800C; with activation energies of about 30kJ/mol and 164 to 181kJ/mol, respectively. The material became a proton conductor in H or CH4 at 500 to 900C, with a proton conductivity of between 0.001 and 0.01S/cm. This was 2 to 3 orders of magnitude higher than the electronic or O ionic conductivity in air or O. The activation energy for proton conduction was equal to 49kJ/mol in CH4 and 54kJ/mol in H. The conductivity in water vapor-saturated N, air or O was higher than that in the corresponding gas without water vapor. The presence of water vapor did not affect the conductivity in H or CH4. Gas permeation measurements showed that membranes of the present material were impermeable to H when the membrane was exposed to H or CH4 upstream and to N or O downstream. The results confirmed that this was a pure proton conductor, with very low electronic and O ionic conductivities.

Electrical Conducting Properties of Proton-Conducting Terbium-Doped Strontium Cerate Membrane. X.Qi, Y.S.Ling: Solid State Ionics, 1999, 120[1-4], 85-93