Hydrothermal-synthesized mesoporous nickel oxide nanowall arrays with enhanced electrochromic application

Mesoporous NiO nanowall arrays are prepared by a facile hydrothermal synthesis method in combination with a following annealing process. The as-prepared NiO nanowalls have average diameters of ∼10 nm and composed of interconnected nanoparticles ranging from 5 to 30 nm. The NiO nanowall arrays show a hierarchical porous structure from mesopores of 5–20 nm to macropores of 30–200 nm. The electrochromic performances of the NiO nanowall arrays are characterized by means of UV–vis spectroscopy and cyclic voltammetry (CV) measurements. The mesoporous NiO nanowall arrays exhibit much better electrochromic performance with faster switching speed and higher color contrast than the dense NiO film. The mesoporous NiO nanowall arrays show a transmittance variation with 77% at 550 nm, and the coloration and bleaching times are 2 s and 2.5 s, respectively. The improved electrochromic performances are due to the porous morphological characteristics, which provide fast ion and electron transfer resulting in fast reaction kinetics and high color contrast.