Designing Selective Electrode Materials for Electroanalysis –New Tungsten Bronzes as Selective Potassium Hosts

Abstract

Commercially available monoclinic tungsten oxide WO3 (Pearson symbol mP32) is investigated electrochemically for its selectivity and sensitivity towards potassium ion detection. Electroreduction in aqueous potassium chloride solution shows two distinct phases, identified as tungsten bronzes KxWO3 (phase 1: maximum x1 (Formula presented.) 0.1 and phase 2: maximum x2≈0.3). In situ synchrotron powder X-ray diffraction reveals the concomitant structural changes, and both phases are identified as new, so far unreported, perovskite-derived potassium bronzes (space group P4/nmm and I (Formula presented.) 3 m, respectively). In cyclic voltammetry, only the first insertion step is found to be reversible. Potentiostatic insertion and the subsequent voltammetric de-insertion show selectivity toward potassium against lithium and sodium in 0.1 M aqueous solutions. The sensitivity towards potassium is analysed in a concentration range between 1 mM and 100 mM. Two linear regions are found for the response, which we relate to two different rate-determining steps, depending on the concentration of potassium in solution.