Nanosize hexagonal tungsten oxide for gas sensing applications

Tungsten oxides and tungsten oxide hydrates are among the most used materials in electro-, photo- and gaso-chromic applications. Lately, tungsten oxides have been commonly applied as sensing layers for hazardous gas detection as well. In this work, a soft chemical nanocrystalline processing route has been demonstrated for the preparation of hexagonal tungsten oxides. The acidic precipitation was followed by hydrothermal and heat treatments at low temperatures. The morphology of parent phases, such as amorphous WO₃·2H₂O, orthorhombic WO₃·1/3H₂O, and resulting oxides with open structured nanosized hexagonal platelets of h-WO₃ particles have been studied by scanning electron microscopy (SEM), by conventional transmission electron microscopy (TEM) and by high resolution transmission electron microscopy (HRTEM). Structural and electrochemical performance of thin films have been determined by atomic force microscopy and cyclic voltammetry. The ion insertion properties of tungsten oxide hydrate and tungsten oxide films show a clear dependence on the presence of structural water and on the close packed structure. Sensing properties of the prepared tungsten oxides have been tested with respect to ammonia gas.