Controllable crystallization engineering on amorphous tungsten oxide nanoparticles for highly efficient photochromic response

Abstract

Photochromic materials are promising for application in the smart window, but typical WO 3 chromogenic ceramics suffer from slow color-switching speed and limited color saturation. Rational construction of amorphous–crystalline ( a–c ) heterostructure offers infinite expectations for developing WO 3 -based composites with a highly efficient photochromic response. Here, the controllable modulation of the WO 3 crystallization for synthesizing a-WO 3 /c-WO 3 hetero-nanoparticles is reported by modulating the ratio of acetic acid/sodium tungstate precursors via the synchronous dual-phase synthetic strategy. Owing to the hierarchical structure of crystalline WO 3 self-embedded amorphous WO 3 , the ultraviolet sensitivity, color difference, and light comprehensive reflectance of the hetero-nanoparticles are enhanced by 4.25, 1.87, and 1.52 times, respectively, compared with pure amorphous WO 3 . Spectroscopic and photoelectrochemical results reveal that hetero-nanoparticles switched from yellow WO 3 to the blue H x WO 3 accompanied by an increased free carrier density, positively shifted energy levels, and narrower bandgap. For the improved photochromic response, it is ascribed to the concerted advantages of each component and the resultant strong a–c interface interaction, promoting water decomposition in the protons supply, charge transfer in the surface hydration layer, and proton intercalation in the ion-to-electron transducer layer. This work enriches the preparation avenue and mechanism interpretation for WO 3 -based photochromic nanocomposites that exhibit NIR shielding properties. • Amorphous–crystalline WO 3 photochromic hetero-nanoparticles are synthesized by using acetic acid. • The hetero-nanoparticles display faster color-switching speed and higher coloration efficiency. • Photochromic behavior increases the free carrier density, shifts the energy level, and narrows the bandgap. • The concepts of protons supply layer, surface hydration layer, and ion-to-electron transducer layer are introduced. • The synergistic effect between hybrid components triggers efficient charge transfer and protons insertion.