STRUCTURAL AND SPECTROELECTROCHEMICAL INVESTIGATIONS OF SOL-GEL DERIVED ELECTROCHROMIC SPINEL CO3O4 FILMS

Thin films of the cubic spinel Co3O4 were prepared by the sol-gel rout e from a Co(II) sulfate precursor using a dip-coating technique. The f ilms (50 to 60 nm thick) were deposited on indium-tin oxide glass subs trates with a single dipping. The electrochromic properties of the fil ms mere studied in an aqueous alkaline electrolyte (0.1 M LiOH) using cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemistry. Th e intermediate oxide products that appeared during cycling at current peak potentials were analyzed by x-ray diffraction (XRD) and ea: situ Fourier transform infrared (FTIR) reflection-absorption spectroscopy p erformed at near-grazing incidence angle conditions (NGIA), High hydra tion of the spinel structure enables complex redox processes to take p lace inside the structure or on the surface of the film when potential cycling is performed. Vibrational bands characteristic of the formati on of CoO, Co(OH)(2), and hydrated Co3O4 phases have been assigned and discussed according to the results obtained from ex situ NGIA FTIR, C V, and XRD studies. The change in transmittance (lambda = 634 ma) betw een bleached and colored states for single-dipped films was 25%, and f or electrochromic efficiency (eta) Was approximately 25 cm(2) C-1.