Enhanced electrochromic properties and amphoteric coloration of V-doped WO3 supported by electronic structure optimization and oxygen vacancy-mediated Li+ capture structures†
Abstract
As one of the most valuable electrochromic materials with in-depth multi-disciplinary applications, tungsten oxide (WO3) has the advantages of strong energy-saving ability and good environmental adaptability, but its poor coloring efficiency and short cycle life limit its commercial application. Here, V-doped WO3 electrochromic thin films (WO3-V-X%, X = 0, 1, 5, 10) with amphoteric color-changing properties were prepared using simple hydrothermal and annealing methods, which were enhanced by electronic structure optimization and oxygen vacancy-mediated Li+ trapping structures. Compared with the pure WO3 films, the Li+ diffusion rate of 1% V-doped WO3 (5.733 × 10−10 cm2 s−1) is 1.7 times higher than that of pure WO3 (3.345 × 10−10 cm2 s−1). The calculations based on density functional theory (DFT) showed that the electrochemical properties of the films were improved due to the change of the localized reduction properties of WO3 after V doping, which significantly modulates the electronic structure and serves as a structural support. Meanwhile, oxygen vacancies (VO) are formed when V is doped, and the presence of VO can trap Li+ to provide more diffusion and binding sites, which improves the diffusion rate of Li+ in doped WO3 films. Therefore, the improved electrochromic performance can be attributed to the stabilizing effect of V doping, the adsorption of Li+ after the formation of VO and the synergistic effect of the two together promote the rapid diffusion of ions and the rapid charge transfer in the films. This unique modulation strategy and facile synthesis route will open up new avenues for the modification and development of electrochromic materials.