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 (V_O) are formed when V is doped, and the presence of V_O 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 V_O 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.