Cathodic insertion of ions in tungsten(VI) oxide from aqueous media

Abstract

Electrochemical insertion of ions in monoclinic tungsten(VI) oxide from aqueous solutions was investigated at room temperature. The solutions were nitric acid and solutions of Group I and II nitrates. In all the performed insertions, except with lithium nitrate, the obtained intercalates had the composition H_xWO₃ (0.07 < x < 0.84). Within this compositional range two types of hydrogen intercalated materials were obtained, both with tetragonal symmetry. For low degrees of insertion (0.07 < x < 0.17) the lattice constants were a = b = 5.225(2) and c = 3.884(4) Å. For high degrees of insertion (0.50 < x < 0.84) the lattice constants were a = b = 5.358(2) and c = 3.749(5) Å. With lithium nitrate as electrolyte solution intercalates with composition Li_xWO₃ were obtained. After exposure to air the lithium intercalated compounds were tetragonal with lattice constants a = b = 5.1996(2) and c = 3.8402(1) Å. The processes where barium nitrate was used as electrolyte were studied in detail, and the electrochemical processes were determined. The intercalates were characterized using X-ray powder diffraction, and Rietveld refinements of the structures of H_0.12WO₃ and Li_xWO₃ were performed.