Synthesis and characterization of electrochromic plate-like tungsten oxide films by acidic treatment of electrochemical anodized tungsten

Tungsten films on ITO glass were anodized into a porous amorphous WO3 film morphology at 60 V. The follow-up acidic treatment of the anodized WO3 films in H2SO4 solution transformed the morphology into plate-like WO3·2H2O. Glancing incident X-ray diffraction and Raman scattering spectra indicated that the growth of plate-like WO3·2H2O films was caused by a dissolution-precipitation reaction in H2SO4 solution. The plate-like WO3·2H2O transformed into monoclinic WO3 by dehydration at 400 °C, and it collapsed into a dense particle-like one at 500 °C due to the strain of dehydration. Due to its highly porous plate-like morphology, the 400 °C-annealed WO3 film has the highest optical modulation of 52% and coloration efficiency of 71 cm2/C at 633 nm.