Further XRD characterization of electrochromic nickel oxide thin films prepared by anodic deposition

Electrochromic (EC) behaviour of nickel oxide (NiOx) thin films, formed by potentiostatic electrodeposition in a nickel ammine complex solution (Ni(NH3)x2+; pH 9), were investigated using alkaline electrolyte solutions, KOH and (CH3)4NOH (pH 12.9). In both electrolytes, the fully oxidized composite films (F0.7/1.1), prepared by electrolysis at 1.1 V (vs. Ag/AgCl) followed by electrolysis at 0.7 V, commonly showed broadened UV–VIS spectra in the visible and near IR region compared with that prepared at 1.1 V (F1.1). Characterization of as-prepared, oxidized and reduced films in the electrolytes by low angle fixed X-ray diffraction (LAXRD) was performed to explain in detail the mechanism of the EC transformation of the films based on the conversion between two types of layered structure, α-Ni(OH)2/γ2-2NiO2·NiOOH or β-Ni(OH)2/β-NiOOH. A model according to the extraction/insertion of cations or water molecules from/into the interlayer was proposed.