Three types of super-acidic sulfated zirconia were prepared by various means, using hydrated zirconia and sulfuric acid. The proton conductivities were evaluated at 20 to 150C under a saturated water vapor pressure. It was found that the SOx concentration on sulfated zirconia varied markedly; depending upon the preparation method. The S/Zr atomic ratio changed from 0.046, for samples prepared from a mixture of hydrated zirconia powder and sulfuric acid, to 0.35 for samples prepared from a mixture of hydrated zirconia sol and sulfuric acid. A powder compact of the former sulfated zirconia exhibited a proton conductivity of 4 x 10−2S/cm at 70C and 8 x 10−3 S/cm at 150C. That of the latter sulfated zirconia exhibited a high conductivity of 5 x 10−2S/cm at 60 to 150C. The electronic polarization induced by SOx was assumed to improve the Lewis and Brønsted acidities on Zr; leading to higher proton conductivities.

Proton Conductivity of Superacidic Sulfated Zirconia. S.Hara, M.Miyayama: Solid State Ionics, 2004, 168[1-2], 111-6