Electrochemical sensors based on transition metal oxide bronzes

Abstract

Tungsten and molybdenum oxide bronzes of the general formulas A_xMO₃ and A_xM₆O₁₇ (A=K, Li, Na; M=W, Mo) are well known as electrode materials with good response to pH changes. However, there is also a high cross sensitivity to other ions, e.g. Na⁺ or Li⁺. Currently, the synthesis of tailored materials for special applications is the priority task. Preparation routes such as fused salt electrolysis, solid state reactions in vacuum or hydrothermal synthesis were studied. New compounds of the general formula Li_xMo_1−yW_yO₃ and also A_xWO₃ (A = bi- or trivalent) have a high technological potential. Preliminary experiments have shown that some of these new materials possess properties of reference electrodes within a restricted pH range. To prepare electrodes, usually single crystals are required. This is adverse because of high operating expense of single crystal synthesis. In some cases it is also possible to use polycrystalline materials for the preparation.