Simultaneous visualization and quantification of real-time charge in a smart electrochromic supercapacitor based on a wisteria-like polyoxometalate/W18O49 nanowire composite

Novel materials with highly synchronized electrochromic (EC) and energy storage properties are needed to simultaneously visualize and quantify the real-time charge state of energy storage devices. Herein, a film was prepared by the Layer-by-Layer assembly of W18O49 nanowires and a Preyssler-type polyoxometalate (POM) [P5W30O110]15− (P5W30). The introduction of amorphous POM decreased the band gap to 2.54 eV, which greatly facilitated the synergy between the EC and charge storage properties. Driven under a low voltage of −0.6 V, this W18O49/P5W30 composite film displayed strong and reversible changes in its optical absorbance in both the visible and near-infrared regions, and it also showed the typical pseudocapacitance behavior with an area capacitance of 34.71 mF cm−2. Moreover, this film was able to simultaneously quantify and visualize its own energy storage state and photothermal conversion in real time by significant color changes (maximum chromaticity difference: 72.44) and high absorbance changes (1.11 at 650 nm and 1.11 at 1200 nm). In addition, a gel EC supercapacitor based on the W18O49/P5W30 film as cathode and NiO film as anode exhibited an absorbance variation up to 0.75 and an area capacitance as high as 4.42 mF cm−2, and it successfully powered a light emitting diode using the stored electrical energy. This work not only broadens the application scope of POM-based EC materials but also provides a feasible design strategy for next-generation smart energy storage devices.