Vanadium substituted Keggin-type POM-based electrochromic films showing high performance in a Li+-based neutral non-aqueous electrolyte

In this research, three vanadium substituted polyoxometalates (POMs) K3+n[PW12−nVnO40] (abb. PW12−nVn) (n = 1, 2, 3)-based electrochromic (EC) films were prepared using the electrodeposition method. The films not only show a good performance in terms of EC properties in an H+-based aqueous electrolyte, but also show good EC performance in a Li+-based non-aqueous electrolyte. Although the EC activity of POMs is lower in the neutral media than in acid media, the use of the neutral non-aqueous electrolyte does not result in the suppression of the EC performance. The large diffusion coefficient of the Li+ in the porous films guarantees the high performance. For the PW11V, PW10V2 and PW9V3-based films, the coefficients of Li+ are 4.05 × 10−11, 4.11 × 10−11, and 1.04 × 10−11 cm2 s−1, respectively. The PW10V2-based film shows the shortest response time for coloration which is even shorter than that shown in the H+-based aqueous electrolyte. The optical contrast of the films is also nearly the same as which achieved in the aqueous electrolyte media. The application of the non-aqueous neutral electrolyte would be beneficial for the fabrication of the POM-based EC device.