The Performance Tuning Of The Electrochromic Materials Based On Polyoxometalates

Electrochromic materials have received much attention in chemistry and materials science owing to their potential applications in smart windows, displays and car rear-view mirrors. Polyoxometalates (POMs) represent a well-known class of structurally well-defined metal oxide nanoclusters. POMs are promising candidates due to their diverse structures and good reversible redox activity.In this paper, we focus on the fabrication of POMs-based film materials by layer-by-layer method (LbL) and investigation of the electrochromic performances.1 We successfully fabricated the multilayer film composed of the polyoxometalate cluster K10[P2W17O61] (P2W17), Neutral Red (NR) and polyallylamine hydrochloride (PAH) by the LbL method. The characterization of UV-vis spectroscopy reveals that POM, PAH and NR were constantly deposited in the ultrathin films. The surface morphology was investigated by SEM, which is uniform and smooth. This composite film demonstrates color changes from deep pink to light purple, then to dark purple-blue, achieving tunable color of electrochromic material. Furthermore, the different color can be considered as different spectral signal. Therefore, the composite film may become a promising candidate for application in tunable-color electrochromic devices and data-storage devices.2 We reported the preparation of multilayer film consisting of tungstophosphate (P2W18), PAH and TiO2 by the LbL technique. The composite film was characterized by UV-vis spectrum, scanning electron micrpscopy (SEM), cyclic voltammetry (CV) and chronoamperomtric (CA). The characterizations of UV-vis spectrum and CV confirm the incorporation of P2W18 and TiO2 into the composite film. The composite film displays enhanced electrochromic stability due to the presence of TiO2. The performance of high optical contrast, suitable response time and low operation potential and long-term stability should be promising to meet the requirement for electrochromic devices.3 A composite film containing P2W18, PAH and poly(3,4-ethylenedioxythiophene) (PEDOT) was fabricated by smart combination of LbL with electro-polymerization methods. The multilayer film is synthesized by forming P2W18 layer with PAH using the LbL technique, followed by deposition of PEDOT layer using electro-polymerization in aqueous solution. From the experimental results, the composite film displays enhanced electrochromic performance by combination of PEDOT with P2W18, resulting in the optical contrast of 54.7% at 600 nm and the absorbance without noticeable change upon 1500 cycles. Furthermore, the film provides broader absorption throughout the visible region. Spectroelectrochemical investigation demonstrates that both PEDOT and P2W18 synchronously contribute to electrochromic coloration. The existence of polyelectrolyte PAH in a condensed, coiled conformation is responsible for enhanced stability. These results demonstrate the essential role of POMs in improving functionality on PEDOT. The smart combination of LbL and electro-polymerization methods provides a convenient means to create new materials based on both PEDOT and POMs.4 We successfully constructed a nanocomposite film containing P2W18, carbon nanotubes (CNTs) and chitosan (CS) by LbL method. Chitosan was chosen as cationic polyelectrolyte for dispersing CNTs to form a stable CS-CNTs composite, which was assembled with anionic P2W18. The composite material displays enhanced electrochromic performance, with the optical contrast of 20.3% and coloration efficiency of 91.5 cm2 C-1 at 620 nm. Furthermore, the film displays the increased thickness and surface roughness by incorporation of CNTs into the P2W18 film. Obviously, the presence of CNTs has the strong influence on the multilayer structure, leading to high optical contrast and coloration efficiency. The results demonstrate the essential role of CNTs in enhancing electrochromism on POMs.