Selectivity problem of SnO2 based materials in the presence of water vapors

We report on a comparative analysis of the sensing properties for two-component nanodispersed oxide systems: SnO2–MetOx (Met = Ti, Zr, Hf, Y and La) and SnO2–noble metals (Pd, Pt, Rh and their binary mixtures). The sensor signals towards 20 ppm H2 as a function of temperature (50–550 °C) and ambient humidity (0, 20, 50 and 80% RH at 25 °C) were compared in the light of surface hydroxyls, studied by FTIR and TGA. Cross-sensitivity tests towards H2 in the presence of H2O and towards H2O in the presence of H2 were used to better understand the poor selectivity of SnO2 doped with noble metals. The latter was explained by interaction of H2 and H2O with the same surface species (most probably surface oxygen). The better selectivity of blank SnO2 and SnO2–MetOx (especially SnO2–TiO2) seems to be related to the interaction of H2with surface hydroxyls, which are supposed to be inactive for direct water chemisorption.