Characterization of electrochromic nickel oxide thin films prepared by anodic deposition

Abstract

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 β-NiOOH and β-Ni(OH)₂, i.e. involving the redox reaction Ni³⁺+ e ⇄ Ni²⁺.