Pure inorganic multi-color electrochromic thin films: vanadium-substituted Dawson type polyoxometalate based electrochromic thin films with tunable colors from transparent to blue and purple

Abstract

A polyoxometalate (POM)-based pure inorganic multi-color electrochromic thin film is reported. The films are fabricated by a facile solution-based electrodeposition method. One to three vanadium atoms substituted Dawson type POMs α-K_6+n[P₂W_18−nV_nO₆₂]·18H₂O (n = 1, 2, 3) are used as electrochromic materials. With the increase of the amount of vanadium atoms in the molecule, multi-color changes are detected gradually and the performances are also enhanced with the increase of the amount of vanadium atoms. The tri-vanadium substituted POM-based film reveals the highest performance among the three films whose optical contrast is up to 91.8%, and response time for coloration and bleaching is 3.5 s and 3.9 s, respectively. It has a coloration efficiency of 176.8 cm C⁻¹ and shows maximum absorption peak shifts at 586 nm, 577 nm and 555 nm followed by the increase of the applied potential. The performances of the films do not show obvious changes after the test of 1000 cycle’s consecutive double-potential step chronoamperometric experiments which indicate their good durability.