Enhanced electrochromic performance of nanoporous NiO films

NiO films have been prepared via sol–gel dip coating method at 300 °C followed by annealing them at 300 °C for different durations (15–60 min). XRD spectra of the films reveal the amorphous nature of the films annealed for 15–45 min. The films annealed for 60 min exhibit crystalline nature with particle size of 7 nm. Good amount of porosity with an average pore size of 46 nm could be observed through the field emission SEM images for the films annealed for 30 min. The electrochromic properties have been studied using cyclic voltammetry (CV) and in-situ spectro-electrochemical techniques. The films annealed for 30 min exhibit maximum anodic/cathodic diffusion coefficient values. The same films exhibit the maximum color change (82.5%) with photopic constrast ratio of 12.16. The colouration and bleaching time of these films was 3.5 and 1.3 s, respectively. The films annealed for 30 min at 300 °C appear to show optimal electrochromic properties.