Synthesis and electrochromic properties of Ti-doped core-shell crystalline@amorphous WO3 nanowire composite films
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摘要: WO3的结晶程度对其电致变色特性有很大影响，本研究首先使用溶剂热法制备晶态WO3垂直纳米线阵列，随后采用磁控溅射技术在其表面包裹一层Ti掺杂氧化钨(WO3-Ti)非晶态薄膜，从而得到晶态WO3@非晶态WO3-Ti核壳复合阵列结构。通过SEM与TEM可以观察到非晶态薄膜的厚度约为3~7 nm，并且非晶层的沉积并不破坏纳米线阵列结构。相比于纯WO3纳米线，核壳纳米线的吸收峰发生了轻微红移，且XPS检测到复合前后W4f与Ti2p特征峰产生了明显的峰位移动，显示出核壳之间存在着界面交互作用。优化后WO3@WO3-Ti核壳纳米线的响应速度和着色效率分别是纯WO3纳米线的2倍与1.8倍，在可见光和近红外区域都显示出良好的光学对比度，并且具有优异的循环稳定性，经过3000圈循环后对比度保持率可达95.8%。
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关键词:
- WO3晶态纳米线 /
- WO3-Ti非晶态薄膜 /
- 核壳结构 /
- 电致变色
Abstract: The degree of crystallinity of WO3 has a great influence on its electrochromic properties. In this study, crystalline WO3 vertical nanowire arrays were first prepared by solvothermal method, and then a layer of Ti doped tungsten oxide (WO3-Ti) amorphous film was wrapped on the surface by magnetron sputtering technology to obtain crystalline WO3@ amorphous WO3-Ti core-shell composite array structure. It can be observed by SEM and TEM that the thickness of the amorphous film is about 3-7 nm, and the deposition of the amorphous layer does not destroy the nanowire array structure. Compared with pure WO3 nanowires, the absorption peaks of core-shell nanowires have a slight red shift, and XPS detected that the characteristic peaks of W4f and Ti2p before and after recombination have shifted significantly, confirming an interfacial interaction between the shell and the core. The switching speed and coloring efficiency of the optimized WO3@WO3-Ti core-shell nanowires are 2 times and 1.8 times that of the pure WO3 nanowires and the heterostructures exhibit good optical contrast in both visible and near-infrared regions, and have excellent cycling stability, with a contrast retention rate of 95.8% after 3000 cycles. -
图 1 WO3@WO3-Ti核壳纳米线的形成过程示意图
Figure 1. Schematic illustration of the formation process of the WO3@WO3-Ti core-shell nanowire
FTO—F doped SnO2 conductive glass
图 2 纯WO3纳米线 ((a), (b)) 和WO3@WO3-Ti复合纳米线 ((c), (d)) 的SEM图像
Figure 2. SEM images of bare WO3 nanowires ((a), (b)) and WO3@WO3-Ti composite nanowires ((c), (d))
图 3 空白FTO导电玻璃 (a) 和复合前后纳米线 (b) 的XRD图谱
Figure 3. XRD patterns of blank FTO conductive glass (a) and nanowires before and after composite (b)
图 4 纯WO3纳米线 ((a)~(c)) 和WO3@WO3-Ti复合纳米线 ((d)~(f)) 的TEM图像；((h)~(j)) 复合纳米线 (g)的EDS元素能谱图
Figure 4. TEM images of bare WO3 nanowires ((a)-(c)) and WO3@WO3-Ti composite nanowires ((d)-(f)); ((h)-(j)) EDS elemental maps of the composite nanowire shown in (g)
图 5 (a) WO3@WO3-Ti复合纳米线的拉曼光谱；纯WO3纳米线和WO3@WO3-Ti复合纳米线的XPS测试全谱(b) 和W4f图谱 (c)；(d) WO3@WO3-Ti复合纳米线的Ti2p图谱
Figure 5. (a) Raman spectra of WO3@WO3-Ti composite nanowire; XPS survey spectra (b) and W4f spectrum (c) for the bare WO3 nanowires and WO3@WO3-Ti composite nanowires; (d) Ti2p map for WO3@WO3-Ti composite nanowires
图 6 WO3纳米线 (a) 和WO3@WO3-Ti复合纳米线 (b) 的循环伏安曲线；(c) 扫描速度为50 mV/s的CV曲线；(d) 扫描速率的平方根与峰值电流密度的变化曲线
Figure 6. Cyclic voltammetry curves of WO3 nanowires (a) and WO3@WO3-Ti composite nanowires (b); (c) CV curves at a scan rate of 50 mV/s; (d) Square root of scan rate versus peak current density
图 7 WO3纳米线 (a)，WO3@WO3-Ti复合纳米线 (b) 和Ti掺杂WO3(WO3-Ti)薄膜 (c) 的透过率光谱；(d) 复合纳米线的变色实物照片
Figure 7. Transmission spectra of WO3 nanowires (a), WO3@WO3-Ti composite nanowires (b), Ti-doped WO3 (WO3-Ti) films (c); (d) Photo of the discoloration of composite nanowires
图 8 (a) 纯WO3纳米线和WO3@WO3-Ti复合纳米线的紫外吸收光谱图；(b) WO3薄膜和Ti掺杂WO3(WO3-Ti)薄膜的紫外吸收光谱图
Figure 8. (a) UV absorption spectra of bare WO3 nanowires and WO3@WO3-Ti composite nanowires; (b) UV absorption spectra of WO3 film and Ti-doped WO3 (WO3-Ti) film
图 9 (a) 材料的原位着色/褪色转换响应曲线；(b) Ti掺杂WO3(WO3-Ti)薄膜；WO3纳米线 (c) 和WO3@WO3-Ti复合纳米线 (d) 的着色效率(CE)曲线(∆OD表示光密度的变化)
Figure 9. (a) In situ coloration/bleaching switching responses of materials; Coloring efficiency (CE) curves of (b) Ti-doped WO3 (WO3-Ti) films; WO3 nanowires (c) and WO3@WO3-Ti composite nanowires (d) (∆OD represents the change in optical density)
图 10 WO3@WO3-Ti核壳纳米线中Li+离子传输示意图
Figure 10. Schematic diagram of Li+ ions transport in WO3@WO3-Ti core-shell nanowires
图 11 WO3@WO3-Ti核壳纳米线的动态透过率测量 (a) 和相应的计时电流数据 (b)
Figure 11. Dynamic transmittance measurement (a) and the corresponding chronoamperometry data (b) of WO3@WO3-Ti core-shell nanowires
表 1 纯WO3纳米线，Ti掺杂WO3(WO3-Ti)薄膜和WO3@WO3-Ti复合纳米线的电致变色性能比较
Table 1. Comparisons of the electrochromic properties of bare WO3 nanowires, Ti-doped WO3 (WO3-Ti) thin films and WO3@WO3-Ti composite nanowires
Sample Optical contrast/% Coloring time tc/s Bleaching time tb/s Coloring efficiency/
(cm2·C−1)WO3 70.3 6.6 1.6 53.5 WO3-Ti 8.4 1.7 0.3 42.5 WO3@WO3-Ti 74.2 3.2 0.8 96.5 
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