Improved electrochromic performance of hierarchically porous Co3O4 array film through self-assembled colloidal crystal template

A hierarchically porous cobalt oxide (Co3O4) array film, in which the skeleton is composed of ordered non-close-packed bowl array possessing nanoporous walls, is successfully prepared by electrodeposition through self-assembled monolayer polystyrene sphere template. As an anodic coloring material for electrochromic application, the hierarchically porous Co3O4 array film exhibits enhanced electrochromic properties with higher optical modulation, faster switching speed and better cycling performance, compared to dense Co3O4 film. The porous Co3O4 array film presents a quite good transmittance modulation with 42% in the visible range and also shows good reaction kinetics with fast response time of about 2 s, much higher than those of the dense film (25% and 4.5 s). The better electrochromic performances of the porous film are attributed to its highly porous morphology, which shortens the ion diffusion paths and provides bigger surface area. (C) 2009 Elsevier Ltd. All rights reserved.