Selectivity problem of metal oxide based sensors in the presence of water vapors

We report our recent results on comparative analysis of sensing properties for two-component nanodispersed oxide systems: SnO2–MetOx (Met=Ti, Zr, Hf, Y and La) and SnO2-noble metals (Pt, Pd, Rh). 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 hydroxylation degree, estimated by FTIR and TGA. Poor selectivity of SnO2 doped with noble metals was found and explained by interaction of H2 and H2O with the same surface species (most probably surface oxygen). Rather good selectivity of blank SnO2 and SnO2–MetOx (especially doped with IVB elements) seems to be related with H2 interaction with surface hydroxyls, which are supposed to be inactive for direct water chemisorption.