The synthesis of V(2)O(5)center dot 1.9H(2)O single crystals from VOSO4 by chemical oxidation with H2O2 through means of a hydrothermal route is demonstrated. The textural properties of this oxide are characterized by X-ray photoelectron spectroscopy, high-resolution analysis electron microscopy, X-ray diffraction analysis, and thermogravimetric analysis. The novel redox intercalation ability and ion selectivity for the potassium ion among Li, Na, and K ions reveal its promising application potential to K+ sensors, high-power rechargeable batteries, and the purification of potassium ions in aqueous media. (C) 2004 The Electrochemical Society.