| Summary: | NiO-loaded SnO<sub>2</sub> powders were prepared involving two chemical procedures. The mesoporous SnO<sub>2</sub> support was synthesized by a hydrothermal route using Brij 35 non-ionic surfactant as a template. The nickel loadings of 1 and 10 wt.%. NiO were deposited by the wet impregnation method. The H<sub>2</sub>S sensing properties of xNiO-(1-x)SnO<sub>2</sub> (x = 0, 1, 10%) thick layers deposited onto commercial substrates have been investigated with respect to different potential interfering gases (NO<sub>2</sub>, CO, CO<sub>2</sub>, CH<sub>4</sub>, NH<sub>3</sub> and SO<sub>2</sub>) over a wide range of operating temperatures and relative humidity specific for in-field conditions. Following the correlation of the sensing results with the morphological ones, 1wt.% NiO/SnO<sub>2</sub> was selected for simultaneous electrical resistance and work function investigations. The purpose was to depict the sensing mechanism by splitting between specific changes over the electron affinity induced by the surface coverage with hydroxyl dipoles and over the band bending induced by the variable surface charge under H<sub>2</sub>S exposure. Thus, it was found that different gas-interaction partners are dependent upon the amount of H<sub>2</sub>S, mirrored through the threshold value of 5 ppm H<sub>2</sub>S, which from an applicative point of view, represents the lower limit of health effects, an eight-hour TWA.
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