Thin films of the cubic spinel Co,O4 were prepared by the sol-gel route from a Co(II) sulfate precursor using a dipcoating technique. The films (50 to 60 nm thick) were deposited on indium-tin oxide glass substrates with a single dipping. The electrochromic properties of the films were studied in an aqueous alkaline electrolyte (0.1 M LiOH) using cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemistry The intermediate oxide products that appeared during cycling at current peak potentials were analyzed by x-ray diffraction (XRD) and ex situ Fourier transform infrared (FTIR) reflection-absorption spectroscopy performed at near-grazing incidence angle conditions (NGIA). High hydration of the spinel structure enables complex redox processes to take place inside the structure or on the surface of the film when potential cycling is performed. Vibrational bands characteristic of the formation of CoO, Co(OH),, and hydrated Co,O4 phases have been assigned and discussed according to the results obtained from ex situ NGIA FTIR, CV, and XRD studies. The change in transmittance () = 634 nm) between bleached and colored states for single-dipped films was 25%, and for electrochromic efficiency (ii) was approximately 25 cm2 C'.

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Tungsten oxide films of thicknesses 1095 nm have been cathodically deposited onto ITO coated glass substrates kept at room temperature, at a rate of 13 nm/min. The electrolyte solution has been prepared by adding 0.025 M tungsten (dissolved in 30% H2O2) to 0.25 M H2SO4. XRD observations showed that all films are amorphous. The film resistivity at room temperature was found to be 9 × 106 Ω cm, and from the resistivity–temperature dependence, the thermal activation energy was obtained as 0.29 eV. The refractive index, n, and the extinction coefficient, k, have been computed from the corrected transmittance and reflectance over the spectral range 400 to 800 nm. Absorption versus photon energy curves give an indirect transition with optical energy gap of 3.25 and 3.36 eV for the as‐deposited and coloured states, respectively. The electrochromic properties of the prepared films have been investigated in situ and both solar transmittance and optical density have been evaluated in the coloured and bleached states. The electrochemical coloration and bleaching were performed in an electrolyte of 0.4 M H2SO4 solution. The coloration efficiency has been evaluated as 50 cm2/C at λ = 600 nm, which is comparable with the results obtained from films prepared by other methods.

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