Electrochromic properties of nickel oxide films prepared by the oxidation of nickel-carbon composite films

Electrochromic (EC) nickel oxide (NiO) films were prepared either by plasma oxidation of vacuum-deposited nickel-carbon (Ni-C) composite films or by thermal oxidation of those films. EC properties of the TiO films were measured by cyclic voltammetry in 1 M KOH. The degree of electrochromism in the NiO films depended not only on the Ni-to-C (Ni/C) ratio in the Ni-C films but also on the oxidation conditions of the Ni-C films. The NiO him with a Ni/C ratio of similar to 0.6 showed the longest cycling ability among the films with three different Ni/C ratios (similar to 0.3, similar to 0.6 and similar to 1.2). The NiO film thermally oxidized at 500 degrees C showed smaller transmission modulation and passed charge density than the plasma oxidized film, but could be electrochemically switched for more than 5000 cycles without serious residual coloration.