One-pot preparation of crystalline-amorphous double-layer structured WO3 films and their electrochromic properties

WO3 films with crystalline-amorphous double-layer structure were prepared via one-pot electrochemical synthesis for the first time. According to scanning electron microscopy images combined with X-Ray diffraction patterns, the crystalline layer and the amorphous layer can be distinguished. Results of electrochromic measurements show that the as-synthesized films have shorter response time than crystalline films and better durability than amorphous films. The films were then modified by electrochemical lithiation/delithiation to produce a porous surface and electrochromic behaviors (response time, coloration efficiency, etc.) were studied by controlling the current and cycle times during electrochemical lithiation/delithiation. Response time is shortened and coloration efficiency is improved after electrochemical lithiation/delithiation. The formation of color centers was also analyzed. Increasing the concentration of H+ ions is beneficial to the formation of surface color centers, while increasing the applied current benefits the formation of body color centers.