Structural Water in Amorphous Tungsten Oxide Hydrate Enables Fast and Ultrastable Regulation of Near‐Infrared Light Transmittance

Abstract Amorphous tungsten oxides typically show low near infrared (NIR) light selectivity owing to the overlapped modulation of visible and NIR light originating from ion insertion induced polaronic adsorption, and poor cycling stability due to the ion trapping effects during the repeated ion insertion/extraction. Here it is reported that the structural water in amorphous tungsten oxide hydrate can induce selective and fast modulation of NIR light with extremely high cycling stability. The enhanced NIR electrochromic (EC) capability is found to be associated with the dominant pseudocapacitive behavior promoted by the structural water. The pseudocapacitive EC process avoids the deep ion insertion, slow ion diffusion kinetics, and ion trapping effects that typically occur in conventional diffusion‐controlled EC process, leading to high NIR light selectivity, fast response speed, and exceptional cycling stability. By tuning the amount of structural water, it is found that WO₃·0.9H₂O films show the optimum NIR EC performance with optical modulation of 69%, response times <3 s, coloration efficiency of 312 cm² C⁻¹, and cycling stability of 12 000 cycles at the wavelength of 1100 nm, which represents the state‐of‐the‐art NIR EC performance for the tungsten oxide‐based EC materials, making it a promising material for managing solar heat.