Sodium tungsten oxide nanowires-based all-solid-state flexible transparent supercapacitors with solar thermal enhanced performance

A sodium tungsten oxide (Na_xWO₃) nanowires-based all-solid-state flexible transparent supercapacitor with solar thermal enhanced performance has been developed owing to the good visible light transparency and near infrared (NIR) photothermal conversion property of Na_xWO₃. Firstly, silver nanowires (AgNWs) and Na_xWO₃ nanowires were synthesized by polyol and hydrothermal methods, respectively. Secondly, AgNWs, Na_xWO₃ nanowires and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) were coated on polyethylene terephthalate (PET) film in sequence to yield the AgNWs/Na_xWO₃/PEDOT electrode, which was shown to exhibit good capacitive property in H₂SO₄ solution. Finally, the PEDOT//AgNWs/Na_xWO₃/PEDOT all-solid-state flexible transparent asymmetric supercapacitor was fabricated by using this electrode as the negative electrode, PEDOT:PSS-coated PET film as the positive electrode, and poly(acrylic acid)/sulfuric acid (PAA/H₂SO₄) gel as the electrolyte. It possessed good visible light transparency, flexibility, and capacitive property. Furthermore, its capacitance could be significantly enhanced by solar illumination because the generated heat via NIR photothermal conversion of Na_xWO₃ nanowires could raise the temperature and thereby lower the electrolyte and charge-transfer resistances effectively. The further kinetic analysis confirmed that its solar thermal-enhanced capacitance was mainly contributed by the diffusion-limited process. Moreover, it exhibited good stability and both its energy density and power density could be enhanced by solar illumination. Such a novel supercapacitor might have great potential in the development of flexible transparent energy storage devices with solar thermal enhanced performance.