Plasmonic metal oxide nanocrystals offer tunable near-infrared absorption through localized surface plasmon resonance. However, despite the presence of shape and crystalline anisotropy in some plasmonic metal oxide nanocrystals, such as tungsten oxide, understanding their influence on electrochromic modulation and how to harness these properties remains limited. In this presentation, I will first demonstrate how the distinct optical properties of tungsten oxide nanocrystals can be effectively utilized through the use of Na⁺ electrolytes.[1] I will then discuss how shape and crystalline anisotropy in plasmonic tungsten oxide nanocrystals influence Na⁺-based electrochromic performance. The interplay between these anisotropic features strongly affects both charge capacity and coloration efficiency, which are key parameters governing the extent of electrochromic modulation. Although hexagonal Cs⁺-doped tungsten oxide nanorods exhibit higher coloration efficiency than platelet-shaped nanocrystals, their charge capacity is limited because Cs⁺ dopants hinder Na⁺ insertion into the hexagonal tunnels. Finally, I will highlight dopant engineering of hexagonal tungsten oxide nanocrystals as an effective strategy for overcoming this charge-capacity limitation and further enhancing Na⁺-based electrochromic modulation.[2] By employing NH₄⁺/NH₃ species as removable dopants, these species can be eliminated through simple thermal annealing, thereby opening the hexagonal tunnels for more effective Na⁺ insertion. The resulting increase in charge capacity leads to substantially enhanced electrochromic modulation, reaching a level comparable to that achieved in Li⁺-based electrochromic thin films.
 

Nanocrystals,near infrared,sodium ion,thin film