A smart flexible supercapacitor enabled by a transparent electrochromic electrode composed of W18O49 nanowires/rGO composite films

Abstract

In this study, we fabricated a transparent conductive electrode by co-assembly of Ag and W₁₈O₄₉ nanowires, followed by the deposition of several W₁₈O₄₉ NWs/rGO composite layers. The as-fabricated transparent electrode exhibits tunable transmittance (72–84% at 550 nm) and a conductivity of 23–39 Ω sq⁻¹. Noteworthily, the hybrid film structure made of 15 layers of W₁₈O₄₉ NWs/rGO composite reveals an areal capacitance of 92 mF cm⁻² with a fast and reversible switching response. The electrode can sustain an optical modulation of 94.7% even at a high current density of 10 mA cm⁻². Furthermore, the electrode exhibits excellent electrochromic performance with fast switching speeds (8 s for coloration and 8.45 s for bleaching), high colouration efficiency (46 cm² C⁻¹) and remarkable stability (96.41% of the original optical modulation). A smart bifunctional electrochromic supercapacitor based on this electrode demonstrates a maximum areal capacitance of 48 mF cm⁻² and an energy density of 5.2 μW h cm⁻² with 0.391 mW cm⁻² power density. The device shows excellent mechanical flexibility and stability over 4000 cycles of the charge/discharge test. The dual-functional supercapacitor with a rapid and reversible response and high sustainability in optical modulation (96%) even under high current charge/discharge conditions is promising for real applications.