The large hexagonal tunnels in tungsten oxide nanorods make these materials attractive for Na⁺-based near-infrared electrochromic windows. However, tunnel occupancy by conventional dopants, including Cs⁺, restricts Na⁺ insertion and consequently reduces charge storage and optical modulation. To overcome this limitation, we synthesize NH₄⁺/NH₃-doped hexagonal tungsten oxide nanorods and remove the dopants through a simple thermal annealing process. After annealing at 400 °C, films of NH₄⁺/NH₃-doped hexagonal tungsten oxide nanorods exhibit a charge capacity four times that of their Cs⁺-doped counterparts. Coupled with the high coloration efficiency of the nanorods, this increased capacity enables a 150 nm-thick film to achieve 74% optical modulation at 1200 nm, reaching performance comparable to Li⁺-based systems. Sodium-electrolyte full cells further produce a 20 °C temperature difference between the bleached and colored states. These results demonstrate the importance of dopant engineering in determining electrochromic performance and highlight sodium electrolytes as a viable option for developing next-generation electrochromic windows.
 

WO3-based electrochromic device,LSPR,nanocrystal,colloid