Due to the limited energy resource on earth, energy saving is critical for the sustainable development. Therefore, ways to reduce energy consumption and energy-saving materials are highly desirable. The optical properties (coloring/bleaching) of electrochromic (EC) materials can be changed by a reversible electrochemical process. EC materials are suited to energy saving because the amount of light and heat entering building or automobile can be controlled by changing the transmittance of light. EC materials have shown widespread applications, such as smart windows for energy-saving buildings, low-power displays, self-dimming rear mirrors, electrochromic e-skins, etc. So far, many inorganic and organic materials have been used as EC materials, such as transition metal oxides, Prussian blue, viologens, conducting polymers, and so on. Among these materials, tungsten oxide has attracted considerable attention due to its multiple oxidation states. In this work, W18O49 nanowire was prepared by solvothermal method and sprayed on a PET?ITO (35 Ω square) flexible transparent conductive substrate to obtain W18O49/PET?ITO flexible EC film. The microstructures and valence states of W18O49 nanowire were characterized by XRD, SEM, high-resolution transmission electron microscopy and XPS. The optical modulation range, response time and cycle stability of W18O49/PET?ITO flexible EC film were characterized and analyzed by electrochemical workstation and UV?visible spectrophotometer. The experimental results indicated that the optical modulation range (ΔT) of W18O49/PET?ITO flexible EC film was 23% when the EC film was scanned at the wavelength of 633 nm. The time for colored and bleached switching of W18O49/PET?ITO flexible EC film were 12.8 and 10.6 s when the optical transmittance change of EC film was 90%. Moreover, the W18O49/PET?ITO flexible EC film had excellent cycle stability. The optical transmittance changes of W18O49/PET?ITO flexible EC film was still high (80.9%) when the film was continuous switched between colored and bleached state for 3000 s.
[1]方鲲，毛卫民，吴其晔，等.导电高分子电致变色材料及其在飞机和军事伪装中的应用宇航材料工艺[J].宇航材料工艺, 2004, 6(20):9-13
[2]王颖，李健，顾卡丽.智能变色涂层[J].中国表面工程, 2007, 6(20):9-13
[3]Solis J L, Saukko S, Kish L, et al.Semiconductor gas sensors based on nanostructured tungsten oxide[J].Thin Solid Films, 2001, 391(2):255-260
[4]An S, Park S, Ko H, et al.Enhanced NO2 gas sensing properties of WO3 nanorods encapsulated with ZnO[J].Applied Physics A, 2012, 108(1):53-58
[5]Baeck S H, Choi K S, Jaramillo T F, et al.Enhancement of photocatalytic and electrochromic properties of electrochemically fabricated mesoporous WO3 thin films[J].Advanced Materials, 2003, 15(15):1269-1273
[6] Nandiyanto A B D, Arutanti O, Ogi T, et al.Synthesis of spherical macroporous WO3 particles and their high photocatalytic performance[J].Chemical Engineering Science, 2013, 101:523-532
[7] Li C P, Engtrakul C, Tenent R C, et al.Scalable synthesis of improved nanocrystalline, mesoporous tungsten oxide films with exceptional electrochromic performance[J].Solar Energy Materials and Solar Cells, 2015, 132:6-14
[8]Ren Y, Gao Y, Zhao G.Facile single-step fabrications of electrochromic WO3 micro-patterned films using the novel photosensitive sol–gel method[J].Ceramics International, 2015, 41(1):403-408
[9]Moshofsky B, Mokari T.Electrochromic active layers from ultrathin nanowires of tungsten oxide[J].Journal of Materials Chemistry C, 2014, 2(18):3556-3561
[10]Ou J Z, Balendhran S, Field M R, et al.The anodized crystalline WO3 nanoporous network with enhanced electrochromic properties[J].Nanoscale, 2012, 4(19):5980-5988
[11]Gui Y, Blackwood D J.Electrochromic enhancement of WO3-TiO2 composite films produced by electrochemical anodization[J].Journal of The Electrochemical Society, 2014, 161(14):E191-E201
[12]Kulkarni S B, Mane A T, Navale S T, et al.Synthesis,structural,compositional,morphological and optoelectronic properties of tungsten oxide thin films[J].Journal of Materials Science: Materials in Electronics, 2015, 26(2):1087-1096
[13]Alsawafta M, Golestani Y M, Phonemac T, et al.Electrochromic properties of sol-gel synthesized macroporous tungsten oxide films doped with gold nanoparticles[J].Journal of The Electrochemical Society, 2014, 161(5):H276-H283
[14] Madhavi V, Kondaiah P, Hussain O M, et al.Structural, optical and electrochromic properties of RF magnetron sputtered WO3 thin films[J].Physica B: Condensed Matter, 2014, 454:141-147
[15]Tong M, Dai G, Wu Y, et al.WO3 thin film prepared by PECVD technique and its gas sensing properties to NO2[J].Journal of Materials Science, 2001, 36(10):2535-2538
[16] Denayer J, Aubry P, Bister G, et al.Improved coloration contrast and electrochromic efficiency of tungsten oxide films thanks to a surfactant-assisted ultrasonic spray pyrolysis process[J].Solar Energy Materials and Solar Cells, 2014, 130:623-628
[17]Navarro J R G, Mayence A, Andrade J, et al.WO3 nanorods created by self-assembly of highly crystalline nanowires under hydrothermal conditions[J].Langmuir, 2014, 30(34):10487-10492
[18] Kondalkar V V, Kharade R R, Mali S S, et al.Nanobrick-like WO3 thin films: hydrothermal synthesis and electrochromic application[J].Superlattices and Microstructures, 2014, 73:290-295
[19]Kondalkar V V, Mali S S, Kharade R R, et al.High performing smart electrochromic device based on honeycomb nanostructured h-WO3 thin films: hydrothermal assisted synthesis[J].Dalton Transactions, 2015, 44(6):2788-2800
[20]Guo C, Yin S, Yan M, et al.Morphology-controlled synthesis of W18O49 nanostructures and their near-infrared absorption properties[J].Inorganic Chemistry, 2012, 51(8):4763-4771
[21]Xi G, Ouyang S, Li P, et al.Ultrathin W18O49 Nanowires with Diameters below 1 nm: Synthesis,Near-Infrared Absorption,Photoluminescence,and Photochemical Reduction of Carbon Dioxide[J].Angewandte Chemie International Edition, 2012, 51(10):2395-2399
[22]Zhao Y M, Hu W B, Xia Y D, et al.Preparation and characterization of tungsten oxynitride nanowires[J].Journal of Materials Chemistry, 2007, 17(41):4436-4440
[23]Sun S, Zhao Y, Xia Y, et al.Bundled tungsten oxide nanowires under thermal processing[J].Nanotechnology, 2008, 19(30):4436-4440
[24]Kunyapat T, Xu F, Neate N, et al.Ce-Doped bundled ultrafine diameter tungsten oxide nanowires with enhanced electrochromic performance[J].Nanoscale, 2018, 10(10):4718-4726
[25]Wang J, Khoo E, Lee P S, et al.Synthesis,assembly,and electrochromic properties of uniform crystalline WO3 nanorods[J].The Journal of Physical Chemistry C, 2008, 112(37):14306-14312
[26]Liu J W, Zheng J, Wang J L, et al.Ultrathin W18O49 nanowire assemblies for electrochromic devices[J].Nano letters, 2013, 13(8):3589-3593
[27]Zhou H, Shi Y, Dong Q, et al.Interlaced W18O49 nanofibers as a superior catalyst for the counter electrode of highly efficient dye-sensitized solar cells[J].Journal of Materials Chemistry A, 2014, 2(12):4347-4354
[28]Shirke Y M, Mukherjee S P.Selective synthesis of WO3 and W18O49 nanostructures: ligand-free pH-dependent morphology-controlled self-assembly of hierarchical architectures from 1D nanostructure and sunlight-driven photocatalytic degradation[J].CrystEngComm, 2017, 19(15):2096-2105
[29]Yue C, Zhu X, Rigutto M, et al.Acid catalytic properties of reduced tungsten and niobium-tungsten oxidesApplied Catalysis B: Environmental,2015,163: 370-381[J].CrystEngComm, 2014, 16(30):6866-6872
[30]Cai G F, Tu J P, Zhou D, et al.The direct growth of a WO3 nanosheet array on a transparent conducting substrate for highly efficient electrochromic and electrocatalytic applications[J].CrystEngComm, 2014, 16(30):6866-6872
[31]Lu C H, Hon M H, Kuan C Y, et al.Controllable synthesis of W18O49 nanowire arrays and their application in electrochromic devices[J].Journal of Materials Science, 2015, 50(17):5739-5745
