Sol–gel fabrication of WO3/RGO nanocomposite film with enhanced electrochromic performance

Tungsten trioxide/reduced graphene oxide (WO3/RGO) nanocomposite film was fabricated by the sol–gel spin-coating technique, using a mixed colloidal dispersion of WO3 precursor and GO. The structure, surface morphology and optical properties of WO3 and WO3/RGO films were investigated by means of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and UV-visible spectrophotometry. The electrochemical and electrochromic performances of the WO3 and WO3/RGO films were studied by chronoamperometry, in situ optical transmittance and cyclic voltammogram analysis. In the WO3/RGO nanocomposite film, monoclinic WO3 nanoparticles were grafted onto the surface of RGO sheets via C–W and C–O–W chemical bonds. The results showed that the WO3/RGO nanocomposite film exhibited shorter coloration–bleaching times (tc = 9.5 s and tb = 7.6 s), higher coloration efficiency (75.3 cm2 C−1 at 633 nm), larger optical modulatory range (59.6% at 633 nm) and better cyclic stability compared with WO3 films, which are attributed to faster Li+ ion diffusion and electron transfer rate. The methodology provides a facile and industrially scalable approach to obtain fast switching electrochromic materials.