Electrochromic and electrochemical properties of amorphous porous nickel hydroxide thin films

Nickel hydroxide films were prepared using the chemical bath deposition (CBD) technique. The amorphous nature of the films was confirmed by X-ray diffraction measurements. X-ray photoelectron spectroscopy (XPS) measurements showed that the films exhibited nickel hydroxide nature. The porosity of the films was studied using optical measurements. The electrochromic properties of the porous nickel hydroxide layers were investigated, using cyclic voltammetry, chronoamperometry, in situ transmittance, UV-vis spectroscopy, and impedance spectroscopy. The change in the optical density (ΔOD) was found to be 0.79 for the as-deposited nickel hydroxide films, whereas it is 0.53 and 0.50 for the films annealed at 150 °C and 200 °C, respectively. The in situ transmittance and chronoamperometry curves revealed that the annealed films had a very fast colouration (tc < 290 ms) and decolouration (tb < 130 ms). The measured colouration efficiencies range between 30 and 40 cm2/C. The impedance measurements revealed the faster colouration and good electrochromic properties for the annealed nickel hydroxide films.

► We examined the porosity effect on electrochromic properties of nickel hydroxide. ► CBD is of interest due to its low cost, environmental friendliness. ► Exclusive analysis on XPS measurements of nickel hydroxide samples is presented. ► Improved optical densities and response time (ms) of the samples have been obtained. ► The measured colouration efficiency ranges between 30-40 cm2/C.