Electrobleaching of WO₃ as probed by Raman scattering

The electrobleaching of WO₃ films formed onto a Pt plate by vacuum deposition has been investigated in the aqueous solution containing 0.1 mol/1 H₂SO₄ by Raman spectroscopy. Raman bands due to the WO₃ film did not shift in frequency during the bleaching reaction in the solution but increased in intensity with passing time due to the increase in transmissivity of the chromic WO₃ in the visible region. A fact of particular interest is that at the early stage of bleaching the intensity of Raman scattering from the tungsten oxide increased in proportion to the square root of the elapsed time. This fact strongly suggests that the bleaching rate is conditioned by the diffusion of H⁺ from the oxide phase to the solution phase. Raman bands due to hydration were also observed at the very beginning of the bleaching in the solution, which demonstrates that H₂O as well as H⁺ was injected into the oxide in the coloring process.