Enhanced electrochromic properties of ordered porous nickel oxide thin film prepared by self-assembled colloidal crystal template-assisted electrodeposition

Highly ordered porous NiO film is prepared by self-assembled monolayer polystyrene sphere template-assisted electrodeposition. The as-prepared NiO film shows an ordered hexagonal close-packed bowel-like array that is made up of macrobowls with about 500 nm in diameter. The electrochromic properties of NiO film are investigated in an aqueous alkaline electrolyte (0.1 M KOH) by means of transmittance, cyclic voltammetry and chronoamperometry measurements. The ordered porous NiO film prepared with PS sphere template exhibits a noticeable electrochromism with reversible color changes from transparent to dark brown, and presents quite good transmittance modulation with a variation of transmittance up to 76% at 550 nm. The ordered porous NiO film also shows high coloration efficiency (41 cm2 C−1), fast switching speed (3 s and 6 s) and good cycling performance, compared with the dense NiO film prepared without PS sphere template. The improvements of electrochromic performances are attributed to the highly porous morphology, which shortens the ion diffusion paths and provides bigger surface area.