Polyoxometalates (POMs) demonstrate potential for application in the development of integrated smart energy devices based on bifunctional electrochromic (EC) optical modulation and electrochemical energy storage. Herein, a nanocomposite thin film composed of a vanadium-substituted Dawson-type POM, i.e., K7[P2W17VO62]·18H2O, and TiO2 nanowires were constructed via the combination of hydrothermal and layer-by-layer self-assembly methods. Through scanning electron microscopy and energy-dispersive spectroscopy characterisations, it was found that the TiO2 nanowire substrate acts as a skeleton to adsorb POM nanoparticles, thereby avoiding the aggregation or stacking of POM particles. The unique three-dimensional core−shell structures of these nanocomposites with high specific surface areas increases the number of active sites during the reaction process and shortens the ion diffusion pathway, thereby improving the electrochemical activities and electrical conductivities. Compared with pure POM thin films, the composite films showed improved EC properties with a significant optical contrast (38.32% at 580 nm), a short response time (1.65 and 1.64 s for colouring and bleaching, respectively), an excellent colouration efficiency (116.5 cm2 C−1), and satisfactory energy-storage properties (volumetric capacitance = 297.1 F cm−3 at 0.2 mA cm−2). Finally, a solid-state electrochromic energy-storage (EES) device was fabricated using the composite film as the cathode. After charging, the constructed device was able to light up a single light-emitting diode for 20 s. These results highlight the promising features of POM-based EES devices and demonstrate their potential for use in a wide range of applications, such as smart windows, military camouflage, sensors, and intelligent systems.

Polyoxometalates (POMs) are considered as an attractive option for electrochromic energy storage (EES) system due to their unique electrochemical feature. Herein, a composite film NW/P 2 W 17 /Cu (phen) 2 based on Dawsontype monolacunary POMs K 10 P 2 W 17 O 61 (abbreviated as P 2 W 17 ) and copper complex [Cu II (phen) 2 ](NO 3 ) 2 (abbreviated as Cu (phen) 2 ) formed on TiO 2 nanowire (abbreviated as NW) array substrate was fabricated by hydrothermal process and layer-by-layer self-assembly combination method. This rational designed film NW/P 2 W 17 /Cu (phen) 2 exhibits excellent tunable multicolor electrochromic behavior and improved pseudocapacitive performance with large optical modulation (43.7% at 600 nm), fast switching time (t c = 2.9 s, t b = 9.5 s), and high volumetric capacitance (228.0 F cm À3 at 0.3 mA cm À2 ). In the process of charge and discharge, the composite film can realize the transformation from light green to orange, green, and finally to blue-green color, successfully achieve the bridge between electrochromic behavior and energy storage, and monitor the level of stored energy by color change. This work showed great potential of POMs-based electrode materials for integrated electrochromism and energy storage applications.

Electrochromic supercapacitors (ECSCs) have recently received growing attention for potential smart energy storage components in intelligent electronics. However, in the development of ECSCs, the design and assembly of high-performance electrode...

The key challenge in the practical application of electrochromic energy storage devices (EESDs) is the fabrication of high-performance electrode materials. Herein, we deposited K7[La(H2O)x(α2-P2W17O61)] (P2W17La) onto TiO2 nanowires (NW) to construct an NW–P2W17La nanocomposite using a layer-by-layer self-assembly method. In contrast to the pure P2W17La films, the nanocomposite exhibits enhanced electrochromic and electrochemical performance owing to the 3D sea-cucumber-like microstructure. An EESD using the NW–P2W17La film as the cathode exhibited outstanding electrochromic and energy storage properties, with high optical modulation (48.6% at 605 nm), high switching speeds (tcoloring = 15 s, tbleaching = 4 s), and high area capacitance (5.72 mF cm−2 at 0.15 mA cm−2). The device can reversibly switch between transparent and dark blue during the charge/discharge process, indicating that electrochromic contrast can be used as a quantitative indicator of the energy storage status.