On the pH-sensing properties of differently prepared tungsten oxide filmsol

In this paper, different preparation routes and designs for pH sensing metal/metal oxide electrodes are evaluated. Crystallographic changes in the oxide film are responsible for the pH-sensing capability of tungsten oxide. As the present oxide structure is directly limiting the measuring range, as-received tungsten oxide powders were heat treated to produce polymorphs of WO3, in an attempt to extend the measuring range. Furthermore, electrochemical oxide covered electrodes ranging from micro- down to nano-dimensions have been implemented. Optional coating with Nafion, serving as a membrane material, allows shifting the measuring range even to strongly alkaline conditions.