Electrochromic properties of NiOx prepared by low vacuum evaporation

Nickel oxide (NiOx) thin films were prepared by a low vacuum evaporation (LVE) onto fluorine doped tin oxide (FTO) coated glass substrates. Electrochromic test device (ECTD) was constructed by using these films as working electrodes, together with the FTO/glass as an opposite (counter) electrode in alkaline environment (0.1 M NaOH aqueous solution). Those films exhibited anodic electrochromism, changing color from transparent white-yellowish to dark brown. The coloration and bleaching times, defined as time to reach 23 of the final change in transmittance, were found to be 1.7 and 4.2 s, respectively. ectrochromic characteristics were recorded by using cyclic voltammetry. The optical transmission spectra of the bleached and colored states were recorded in the visible part of the spectrum. The Fourier-transform infrared (FTIR) reflection spectra of the sample in the bleached and colored states were measured at near normal incidence angle. The dependence of the transmission of the sample at wavelength λ=670 nm on the electric charge transported to the anode were also examined. The coloration efficiency was calculated to be 32.4 cm2/C from the slope of the graphical presentation of the optical density as a function of the charge density, during the charge extraction. The spontaneous ex situ change of coloration with time and stability of the sample in the bleached and colored states were also examined.