Photochemical and photoelectrochemical behavior of a novel TiO2/Ni(OH)2 electrode

Transparent Ni(OH)(2) films were electrochemically deposited onto TiO2 layers which had been formed on conductive glass. This optically transparent composite electrode exhibited strong, reversible photochromic and electrochromic properties when either illuminated by a 75 W Xe lamp at open circuit or anodically polarized in 1.0 M aqueous NaOH electrolyte. The extent of electrode darkening depended on the intensity of UV light, exposure time, and applied potential. Electrochemical and optical-absorption measurements indicated that W-photogenerated holes in the TiO2 valence band recombined with electrons from the electrochromic Ni(OH)(2) layer, which consequently oxidized the Ni(OH)(2) tb NiOOH and darkened the composite electrode. Because the darkening process occurred only on the specific electrode areas which were exposed to Light, nonuniform illumination produced a patterned optical state of the;electrode.