High performance visible and near-infrared region electrochromic smart windows based on the different structures of polyoxometalates

Polyoxometalates (POMs) are a kind of metal oxide nanoclusters with excellent electrical properties, which have proved to be an excellent candidate for electrochromism (EC) materials. In this paper, we present a better performance POMs-based EC material on the TiO 2 substrate through adjusting the structure of the Well-Dawson type POMs with the electrodeposition method, which can overcome the high cost of the traditional methods such as vacuum evaporation or sputtering. The performance of the EC smart windows was fully tested. The maximum optical contrast for the K 10 [P 2 W 17 O 61 ]·20H 2 O (P 2 W 17 )-based EC smart window is 93.1% at the wavelength of 620   nm and for the K 6 [P 2 W 18 O 62 ]·14H 2 O (P 2 W 18 )-based EC smart window is 48.7% at 646   nm. The coloration time extracted for a 90% transmittance for the P 2 W 17 -based EC smart window is 0.9   s and for the P 2 W 18 -based smart window is 0.97   s; the coloration efficiency for the P 2 W 17 -based EC smart window is 205.3   cm 2   C −1 and the P 2 W 18 -based smart window is 176.8   cm 2   C −1 . Both of the P 2 W 17 - and P 2 W 18 -based EC smart windows have the feature of remarkable durability over 1000 cycles. The P 2 W 17 -based smart window has larger optical contrast and higher coloration efficiency than the P 2 W 18 -based smart window. More significantly, the near-infrared behavior of the P 2 W 17 under different applied potentials was recorded for the first time by using the smart window. We believe the performance of the P 2 W 17 -based smart window is the state-of-the-art among the POMs-based EC smart windows.