High‐Performance Electrochromic Energy Storage Devices Based on WO3 Nanoflower Via In Situ Intercalation With Polyaniline

Abstract Structural design and interlayer architecture of electrochromic (EC) materials play significant role in their performance. Herein, tungsten trioxide (WO 3 ) nanoflowers have been synthesized through in situ intercalation with polyaniline (PANI), developing a 3D hierarchical structure with optimized interlayered spacing. The PANI‐WO 3 composite showed superior EC stability due to improved ion storage capacity by 3D hierarchical structure with extended surface area for ion interaction. The enlarged layer spacing of PANI‐WO 3 composites allows for accommodating more exchangeable Li + . The PANI‐WO 3 film maintains remarkable cycling stability, retaining 80% of its initial capacity after 30000 cycles. The EC device based on PANI‐WO 3 demonstrates high optical modulation (57% at 633 nm), rapid switching speeds (coloration to 23% in 15 s and bleaching to 80% in 10 s) and high coloration efficiency (168 cm 2 C −1 ). Meanwhile, the PANI‐WO 3 EC supercapacitor achieves a high specific capacitance (121 mF cm −2 at 0.2 mA cm −2 ) and prolonged cyclic life (specific capacity remains at 58% and coulombic efficiency at 65% after 1500 cycles). The PANI‐WO 3 serves as an effective candidate for the fabrication of high‐performance EC devices (ECDs) with potential applications in energy‐saving smart windows, outdoor static displays, and other energy‐efficient technologies.