Highly porous nickel oxide thin films prepared by a hydrothermal synthesis method for electrochromic application

We report NiO nanowall thin films prepared by a facile hydrothermal synthesis method and their electrochromic application. The as-prepared porous nanowall NiO thin films show a highly porous structure built up by many interconnected nanoflakes with a thickness of about 30 nm. The electrochromic performances of the NiO films are characterized by means of UV–vis spectroscopy and cyclic voltammetry (CV) measurements. The effect of the annealing temperature on electrochromic properties is discussed. The NiO nanowall film annealed at 300 °C exhibits much better electrochromic performance than those counterparts annealed at higher temperature. The film annealed at 300 °C exhibits a noticeable electrochromism with reversible color changes from transparent to brown dark and presents a transmittance variation with 77% at 550 nm. The NiO nanowall film also shows good reaction kinetics with fast switching speed, and the coloration and bleaching times are 3 s and 4 s, respectively. The improved electrochromic performances are due to the porous morphological characteristics with fast ion and electron transfer resulting in fast reaction kinetics and high color contrast.