Abstract
Reversible electrochromic mirror by electroplating and electrodissolution of Ag film has been successfully formed onto transparent ITO electrode, without using Ag bromide ion complex. Pd nanoparticles were firstly deposited onto ITO electrode by chronopotentiometry as the pretreatment for forming mirror surface of Ag film. Without Pd nanoparticles on ITO electrode, the deposited Ag film becomes opaque white in appearance because of light scattering from less dispersive and quite large Ag hemispheric crystals on the ITO electrode. However, Ag mirror surface formation also required an addition to the electrolyte in addition to the deposition of Pd nanoparticles on the ITO electrode. Electrolyte additives 2-hydroxypyridine (2-HP) and citric acid were investigated for this purpose. Yellow color smooth Ag mirror surface was achieved at the electroplating condition of the constant cathodic current using 2-HP but electrodissolution of Ag film at the constant anodic current was imperfect due to remaining residue onto ITO electrode and the color of the Ag plating solution (electrolyte) changed from transparent to brown due to the oxidation of this additive. However, when citric acid was used as an additive, a smooth Ag mirror surface was created by electroplating using constant cathodic current. The SEM observation shows anisotropic Ag crystal growth as similar as that for the 2-HP additive. The plating time to form Ag mirror state became shorter than that for the 2-HP additive because the anisotropy ratio of citric acid would be larger than that of 2-HP. The electrodissolution of Ag film at the constant anodic current with citric acid shows that it’s almost back to the transparent ITO electrode at the transmittance of ca. 70% and the solution color of the electroplating bath is colorless and clear.
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