Novel morphology changes from 3D ordered macroporous structure to V₂O₅ nanofiber grassland and its application in electrochromism

Because vanadium pentoxide (V₂O₅) is the only oxide that shows both anodic and cathodic coloration electrochromism, the reversible lithium ion insertion/extraction processes in V₂O₅ lead to not only reversible optical parameter changes but also multicolor changes for esthetics. Because of the outstanding electrochemical properties of V₂O₅ nanofibers, they show great potential to enhance V₂O₅ electrochromism. However, the development and practical application of V₂O₅ nanofibers are still lacking, because traditional preparation approaches have several drawbacks, such as multiple processing steps, unsatisfactory electrical contact with the substrate, expensive equipment, and rigorous experimental conditions. Herein, we first report a novel and convenient strategy to prepare grass-like nanofiber-stacked V₂O₅ films by a simple annealing treatment of an amorphous, three-dimensionally ordered macroporous vanadia film. The V₂O₅ nanofiber grassland exhibits promising transmittance modulation, fast switching responses, and high color contrast because of the outstanding electrochemical properties of V₂O₅ nanofibers as well as the high Li-ion diffusion coefficients and good electrical contact with the substrate. Moreover, the morphology transformation mechanism is investigated in detail. © 2015, Nature Publishing Group. All rights reserved.