High durable TiO2 electrochromic films by Ni doping

Doping with metal ions to enhance the electrochromic performance of single material is attracting widespread attention. In this work, undoped and nickel (Ni)-doped TiO2 electrochromic films with different doping content (0.5, 1, and 5 wt%) were successfully prepared via hydrothermal approach combined with a spin-coated technique. The effect of Ni on the microstructure, morphology, electrochemical and electrochromic performance of TiO2 films were deep studied by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscope (HR-TEM) and X-ray photoelectron spectroscopy (XPS) and UV–Vis–NIR spectrophotometry coupled with an electrochemical workstation. FESEM images show a porous microstructure formation in all the coated films. HR-TEM images show that all the films have a polycrystalline phase with a preferred orientation along the anatase (101) plane of TiO2. The anatase (101) lattice spacing of Ni-doped TiO2 samples were gradually decreased to 0.355 nm, 0.351 nm and 0.342 nm as the doped Ni increased, respectively. XRD proves the HR-TEM result. The electrochemical analysis reveals that the appropriate 1% Ni doping presented the most remarkable electrochromic performance, including that the maximum ions diffusion coefficient of 9.65 × 10–10 cm2/s, the fastest coloring/bleaching switching time of 12.75 s and 1.99 s. Moreover, the 1% Ni-doping TiO2 electrochromic film showed superior cyclic performance–little attenuation occurred after 200 cycles, whereas the undoped sample decayed almost by half after 100 cycles. The study provided valuable insights for promoting the potential applications of nickel metal-doped electrochromic materials.