Chemical and Optical Properties of Electrochromic Nickel Oxide Films

Thin films of nickel oxide-nickel hydroxide are investigated to determine electrochromic switching properties. Crystalline nickel oxide films are synthesized by electrochemical deposition and by anodization of nickel electrodes. Electrochemical deposition using nickel sulfate-based chemistry is used to deposit films directly on doped tin oxide-coated glass. Spectral solar transmittance is obtained for films switched in liquid cells containing a KOH electrolyte. The solar transmittance (Ts) can be switched from Ts (bleached) = 0.73 to Ts (colored)= 0.35 for films with thickness of about 500 Å. Voltammetric data is correlated to known electrochemical processes for nickel electrodes. The nickel oxide films are chemically analyzed using a sputter-Auger microprobe and x-ray photoelectron spectroscopy. As a result of combined analysis, it was determined that these films transform from uncolored to colored states by the reversible transformation of nickel hydroxide Ni(OH)2 to nickel oxyhydroxide NiOOH and that dehydrated films correspond chemically to NiO.

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