context: Next, the annealed WO3−x film was assembled into an electrochromic device to test its functionality. The device structure is shown in Fig. 3a, in which the FTO glass is used as the transparent electrode. The electrolyte with 1.25 M LiClO4 in a mixed solvent was used in the electrochromic device to achieve the insertion and extraction of Li+ ions in the WO3−x film. The device in the bleached state shows a high transmittance in both the visible and infrared wavelength range (Fig. 3b), while in the colored state, the transmittance of the electrochromic device decreases significantly. At the wavelength of 680 nm, the transmittance difference between the two curves is around 70%. In the wavelength range of 700–1000 nm, the transmittance of the colored state is even less than 3%, indicating the excellent near infrared light shielding ability. Hence, in the scorching summer, smart windows made of this electrochromic WO3−x film can keep the room cool by blocking heat radiation. Fig. 3c shows the photographs of the packaged electrochromic device in the coloring and bleaching process. A series of different color states from light to deep blue can be easily obtained by adjusting the applied bias from −3.5 V to 3.5 V, which may have potential applications in the field of electrochromic displays.
answer: 1.25 M LiClO4