Metal doping engineering of W₁₈O₄₉ for excellent dual-band electrochromic smart windows with integrated energy storage function

W₁₈O₄₉ is a promising multifunctional material for electrochromic energy storage applications, owing to its abundant oxygen vacancies and distinctive crystalline structure. However, the contradiction between the high transmittance modulation for electrochromism and the high material loading for energy storage severely restricts the development of W₁₈O₄₉ in multifunctional smart windows. This work found that different metal doping (Mo, Ti, Fe) exhibited significant differences in regulating the electrochromic performance and energy storage of W₁₈O₄₉. And the oxygen vacancies of W₁₈O₄₉ can be further controlled by adjusting the metal doping concentration, simultaneously achieving excellent electrochromic properties and energy storage. 5% Ti-doped W₁₈O₄₉ not only exhibits a high transmittance modulation of 82.3% (633 nm) and 81.0% (1050 nm) with fast coloration/bleaching times of 9.8/5.8 and 3.8/5.8 s, but also shows a good energy storage of 32.5 mF·cm⁻² at 0.1 mA·cm⁻². Theoretical calculations indicate Ti doped W₁₈O₄₉ shows a more delocalized characteristic in band decomposition charge densities and a lower diffusion energy barrier, which is conducive to enhancing the electrochemical performance. This work demonstrates metal doping plays a significant role in simultaneously regulating electrochromism and energy storage, providing a new perspective for the development of multifunctional electrochromic materials.