Humidity-sensing behaviour of surface-modified zirconia

The humidity-sensing properties of one of the most well-known solid superacids, namely, sulfated zirconia, have been systematically investigated in order to correlate the mechanism of humidity sensing with the strength and distribution of acid sites on the surface. The surface-modified zirconia shows an unprecedented resistance change (10(11) to 10(4) Ohm) with change in the relative humidity with a superior slope illustrating better sensitivity compared to normal ceramic oxides. Measurements of adsorption enthalpy for surface-modified and conventional zirconia indicate an energetically favourable interaction of water vapour with the oxide surface in the presence of sulfate species. Morphological characterization using scanning electron microscopy reveals the importance of particle size and surface texture in controlling the humidity-sensing behaviour. In addition, physicochemical characterization techniques like X-ray diffraction and IR spectroscopy have confirmed the role of sulfur species on the surface in causing the high humidity sensitivity.