CHARACTERIZATION OF ELECTROCHROMIC NICKEL-OXIDE THIN-FILMS PREPARED BY ANODIC DEPOSITION

Nickel oxide (NiOx) thin films have been prepared on transparent conducting indium tin oxide (ITO) substrates by anodic deposition from a nickel ammine complex solution. Electrochromic (EC) behaviour of these films was observed in a borate buffer solution at pH 10 in the potential range 0-1 V vs. Ag/AgCl; an as-prepared film (PF) was cathodically reduced to a colourless form (RF) and oxidized to a brown form (OF) by anodic polarization. Characterization of these films by low-angle incident X-ray diffraction and X-ray photoelectron spectroscopy with argon-ion (Ar+) etching revealed that the EC properties are based on the electrolytic transformation of the NiOx structure between beta-NiOOH and beta-NI(OH)2, i.e. involving the redox reaction Ni3+ + e reversible Ni2+.