Jian-Wei Liu, Jing Zheng, Jin-Long Wang, Jie Xu, Hui-Hui Li, Shu-Hong Yu*

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1 Supporting Information Ultrathin 18 O 49 Nanowire Assemblies for Electrochromic Devices Jian-ei Liu, Jing Zheng, Jin-Long ang, Jie Xu, Hui-Hui Li, Shu-Hong Yu* Experimental Section Synthesis and Assembly of 18 O 49 Nanowires. All chemicals are of analytical grade and were used as received without further purification. Synthesis of 18 O 49 nanowires. Uniform 18 O 49 nanowires with high aspect ratios were prepared by a modified hydrothermal method. 1 Briefly, 0.03 g of Cl 6 (Alfa Aesar) and g of Poly(vinyl pyrrolidone) (PVP, Shanghai Reagent Company, M 40,000) were added into 40 ml of ethanol. The mixture was stirred by magnetic stirring to form a homogeneous solution. After the solution was added into a 50 ml Teflon-lined stainless steel autoclave, the container was then closed and maintained at 180 o C for 24 h. After that, the autoclave was cooled to room temperature naturally. After synthesis, the product was centrifuged and washed with absolute alcohol and double distilled water one time to remove the residual surfactants. Assembly of 18 O 49 nanowires by the Langmuir-Blodgett(LB) technique. The ordered 18 O 49 nanowires monolayer was prepared using a modified Langmuir-Blodgett (LB) technique described previously mg of the freshly prepared 18 O 49 nanowires was dispersed into the mixed solution (0.5 ml of N, N-dimethylformamide (DMF) and 0.5 ml of CHCl 3 ) to form a homogeneous solution at room temperature. After that, a 50 µl syringe was used to dispense 18 O 49 nanowire suspension onto the water (Millipore Milli-Q water, resistivity 18.2 MΩ cm) subphase drop by drop in to the LB trough (Nima Technologh, 312D). Thirty minutes later, the nanowires surface layer was then compressed with a compression rate of 20 cm 2 min -1. The constant surface pressure was kept constant as soon as the fold formation that paralleled to the barrier direction occurred. The nanowire films could be obtained by dip-coating. The trough was cleaned by ethanol and CHCl 3 after each experiment. Preparation of electrochromic samples. The different layers of 18 O 49 nanowires by LB technique can be fabricated through parallel assembly of 18 O 49 nanowire monolayer on an Indium tin oxide (ITO) substrate and a type of nanodevice can be constructed. Electrochromic properties of 18 O 49 nanowire nanodevice were investigated with UV-2501PC/2550 and IM6ex electrochemical workstation (Zahner, Germany) at room temperature in air by a three-electrode electrochemical cell with 0.1 mol/l LiClO 4 S1

2 aqueous solution as the electrolyte. In situ coloration/bleaching switching characteristics of the electrochromic film were recorded with an absorbance wavelength of nm by alternately applying voltages of -1.0 and +1.0 V, respectively. Instruments. The X-ray diffraction patterns (XRD) were measured on a Philips X Pert Pro Super X-ray diffractometer equipped with graphite-monochromatized Cu KR radiation. Field-emission scanning electron microscopy (FESEM) was carried out with a field emission scanning electron microanalyzer (Zeiss Supra 40 scanning electron microscope at an acceleration voltage of 5 kv). Raman scattering spectra were recorded with a JY LabRam HR 800 spectrometer using the 514 nm line of Ar+ for excitation. UV-vis spectra were recorded on UV-2501PC/2550 at room temperature (Shimadzu Corporation, Japan).Transmission electron microscopes (TEM) carried out on a commercial JEOL-7650 transmission electron microscope operated at an accelerating voltage of 100 kv. X-ray photoelectron spectra (XPS) were recorded on an ESCALab MKII X-ray photoelectron spectrometer, using Mg KR radiation as the exciting source. High-resolution transmission electron microscope (HRTEM) images were performed on a JEOL-2010 transmission electron microscope operated at an acceleration voltage of 200 kv. The energy-dispersive X-ray spectroscopy (EDS) analysis was also done with a JEOL-2010 TEM with an Oxford windowless Si (Li) detector equipped with a 4-pulse processor Intensity (a.u.) Degree (2θ) Figure S1. XRD spectrum of the as obtained 18 O 49 nanowires. S2

3 60000 Intensity (a.u.) f 5/2 4f 7/ Binding Energy (ev) Figure S2. XPS spectra of the as obtained 18 O 49 nanowire films Intensity (a.u.) Ramanshift (cm -1 ) Figure S3. Raman spectrum of the obtained 18 O 49 nanowire films. S3

4 Counts O C Cu Cu Cu KeV Figure S4. EDS spectrum of the prepared 18 O 49 nanowires. Figure S5. SEM image of the ordered 18 O 49 nanowire film. S4

5 Current Density (macm -2 ) Voltage (V) Figure S6. Current voltage characteristics of ordered 18 O 49 nanowire films on ITO glass as working electrode in 1 M LIClO 4 solution. 100 Transmittance (%) V 0.3V 0V -0.1V -0.3V -0.5V -0.7V -1V avelength (nm) Figure S7. Optical transmittance of ordered five-layer 18 O 49 nanowire films with different applied voltage. S5

6 Figure S8. Electrochromic switching of the ordered 18 O 49 nanowire films. Enlarged plot of figure 3d. Optical transmittance and electrochromic switching monitored at nm for the cycling ability study of 18 O 49 nanowire films at an applied voltage of -1 V for 60 s and 0 V for 60 s for cycles. Figure S9. FTIR spectra (a) and electrochromic performance (b) of the 18 O 49 nanowire films formed on the ITO substrate before (black line) and after (red line) the plasma treatment. S6

7 Figure S10. Electrochromic performances of (a) disordered 18 O 49 nanowire films, (b) ordered 18 O 49 nanowire films at water-air interface by LB trough with the same 18 O 49 nanowire number per unit area. Briefly, we design an experiment by LB trough to compare ordered 18 O 49 nanowire films and disordered one. Firstly, we used Millipore Milli-Q water (resistivity 18.2 MΩ cm) as a subphase filled in the LB trough (Nima Technology, 312D). 1 ml of 1 mg/ml of the freshly prepared 18 O 49 nanowires was dissolved in the mixture of N, N-dimethylformamide (DMF) and CHCl 3 to form a homogeneous solution at room temperature. After that, a 50 µl syringe was used to dispense 18 O 49 nanowire suspension onto the water subphase drop by drop. Thirty minutes later, the nanowires surface layer was then compressed with a compression rate of 20 cm 2 min -1. hen the area of the LB trough turned from 250 cm 2 to 52 cm 2, we found that 18 O 49 nanowires were well aligned. To make disordered 18 O 49 nanowires with the same nanowire density, we directly dropped 1 ml of 1 mg/ml of the freshly prepared 18 O 49 nanowires in the mixture of DMF and CHCl 3 on the interface of LB trough with the area of 52 cm 2. S7

8 Figure S11. (a) π-a isotherms of the 18 O 49 nanowire monolayer obtained at the air/water interface at 25 C. (b) Electrochromic switching of the ordered 18 O 49 nanowire films when the surface pressure creases from 0, to 5, 10, 15, 20, and 30 mnm -1. Firstly, we used Millipore Milli-Q water (resistivity 18.2 MΩ cm) as a subphase filled in the LB trough (Nima Technology, 312D). 1 ml of 1 mg/ml of the freshly prepared 18 O 49 nanowires was dissolved in the mixture of N, N-dimethylformamide (DMF) and CHCl 3 to form a homogeneous solution at room temperature. After that, a 50 µl syringe was used to dispense 18 O 49 nanowire suspension onto the water subphase drop by drop. Thirty minutes later, the nanowires surface layer was then compressed with a compression rate of 20 cm 2 min -1. Figure S11 shows the surface pressure versus surface area (π-a) isotherm of the monolayer of 18 O 49 nanowires. hen the area of the LB trough turned from 250 cm 2 to 52 cm 2, the corresponding surface pressure increased 0 to 30 mnm -1. Figure S11b shows the electrochromic performances of a series of samples obtained at different surface pressures, 0, 5, 10, 15, 20 and 30 mn/m, respectively. Transmittance (%) Time (s) Number of Cycles Figure S12. Stability of electrochromic switching of the as-prepared ordered 20-layer 18 O 49 nanowire films for more than continues 1200 cycles. Reference 1. Xi, G.; Ouyang, S.; Li, P.; Ye, J.; Ma, Q.; Su, N.; Bai, H.; ang, C. Angew. Chem. Int. Ed. 2012, 51, S8