Constructing a hexagonal/orthorhombic WO3 phase junction for enhanced photochromism
Xide Chang, Dong Xu, Xianhua Liu, Yindong Tong, Kaixiang Li, Zhenguo Li, Yiren Lu
Abstract
Mixed-phase composites with an optimal phase ratio show greater light utilization than their monophasic counterparts. This approach can be applied to develop mixed-phase photochromic tungsten oxide (WO 3 ), which shows a rapid photoresponse and high-contrast coloring. Therefore, this paper optimized the phase ratio of hexagonal WO 3 ( h -WO 3 ·0.33H 2 O) and orthorhombic WO 3 ·H 2 O ( o -WO 3 ·H 2 O) to form a homojunction. To enhance its photochromism, nanostructured WO 3 was produced via a one-step hydrothermal strategy, in which its phase structure and morphology were controlled by regulating the reaction temperature during precursor synthesis. Various material characterization techniques were carried out to reveal the complex crystal nucleation and growth of phase junctions. h -WO 3 ·0.33H 2 O nanoparticles dominated the systems, while o -WO 3 ·H 2 O nanoblocks also appeared from 41.77 wt% to 56.50 wt% at a low hydrothermal synthesis temperature, producing a mixture of both polymorphs. The improved photochromic properties (from light yellow to black-green) of the mixed-phase WO 3 composite compared with pure h -WO 3 ·0.33H 2 O (from gray-white to dark gray) was attributed to the formation of a phase junction between h -WO 3 ·0.33H 2 O and o -WO 3 ·H 2 O. The photoelectrochemical results showed that this resulted in highly efficient charge carrier separation and transfer. The strong visual rendering of the black-green state may be useful for developing intelligent displays and similar devices.