W/WO₃/TiO₂ Multilayer Film with Elevated Electrochromic and Capacitive Properties

Electrochromic capacitors, which are capable of altering their appearances in line with their charged states, are drawing substantial attention from both academia and industry. Tungsten oxide is usually used as an electrochromic layer material for electrochromic devices, or as an active material for high-performance capacitor electrodes. Despite this, acceptable visual aesthetics in electrochromic capacitors have almost never been achieved using tungsten oxide, because, in its pure form, this compound only displays a onefold color modulation from transparent to blue. Herein, we have designed W/WO₃/TiO₂ multilayer films by a magnetron sputtering device. The impact of TiO₂ layer on the optical and electrochemical properties was investigated. The results show that the optimum thickness of the TiO₂ layer is 10 nm. The as-prepared film displays a high coloration efficiency (CE) of 74.2 cm² C^-1, a high areal capacitance of 32.0 mF/cm², an excellent rate performance (with the areal capacitance still retaining 87% of the maximum capacitance at a current density of 1 mA/cm²), and a high cycle life (with a capacity retention of 91% after 1000 cycles).