Three‐dimensional knotting of W17O47@PEDOT:PSS nanowires enables high‐performance flexible cathode for dual‐functional electrochromic and electrochemical device

Abstract An efficient integration of electrochromic and electrochemical devices into one flexible entity enables both energy storage and energy‐saving dual‐functionalities. For this purpose, achieving both high electrochromic and electrochemical performance is the key aspect. Herein, a new 3D architecture is successfully made by knotting W 17 O 47 @PEDOT (poly(3,4‐ethylenedioxythiophene)):PSS (poly(styrenesulfonate)) nanowires with NaWO 3 nanoknots, and interestingly, the 3D W 17 O 47 /(NaWO 3 ‐knots)@PEDOT:PSS cathode thus‐made simultaneously exhibits a large optical modulation (79.7% at 633 nm), an ultra‐long cycling life (76% of original optical modulation retained after 12 400 cycles), and a high areal capacitance (55.1 mF cm −2 at 0.1 mA cm −2 ). Our density functional theory (DFT) calculations demonstrate that the much improved dual‐functional performance is correlated to the raised electronic conductivity and ion adsorption at the W 17 O 47 /(NaWO 3 nanoknots) interface, together with the ion adsorption of PEDOT:PSS in the 3D‐knotted architecture. As a proof‐of‐concept application, different‐sized flexible dual‐functional electrochromic/electrochemical devices (FDEDs) were assembled and investigated for various application scenarios, including a smart window (15 cm × 10 cm), a wearable wristband (20 cm × 2.5 cm), and a smart eyeglass. The smart window made of the FDED enables a large temperature difference of 27.6°C confirm‐tested in model houses, where the energy source also powers three light‐emitting diodes (LEDs). The understandings of the key governing principles in the electrodes and dual‐functionalities provide a timely foundation for the new generation flexible multifunctional devices. image