Controlling the Reaction of Nanoparticles for Hollow Metal Oxides Nanostructures

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1 Supporting Information for Controlling the Reaction of Nanoparticles for Hollow Metal Oxides Nanostructures Yong-Gang Sun,, Jun-Yu Piao,, Lin-Lin Hu, De-Shan Bin,, Xi-Jie Lin,, Shu-Yi Duan,, An-Min Cao,*,, and Li-Jun Wan*,, CAS Key Laboratory of Molecular Nanostructure and Nanotechnology, and CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing , People s Republic of China University of Chinese Academy of Sciences, Beijing , People s Republic of China *To whom correspondence should be addressed. anmin_cao@iccas.ac.cn, wanlijun@iccas.ac.cn Experimental Section Materials preparation Synthesis of UNO, UNO@BNO, H-BNO and HM-Nb 2 O 5 nanospheres: 0.63 g of oxalic acid dihydrate, 0.27 g of niobium (Ⅴ) chloride and 0.6 g urea were dissolved in a mixed solution contain 35 ml anhydrous ethanol and 5 ml deionized water under magnetic stirring. After that, the mixture was placed in an oil bath at 80 o C and the obtained precipitation were collected at different reaction stages: Initial precipitation collected after ethanol washing was UNO sample. Heating more than 15 min, the precipitation collected after ethanol washing was UNO@BNO sample. Instead of ethanol treatment, we can obtained H-BNO sample by water washing. The shell thickness of H-BNO depended on the reaction time, which was 50, 80 nm and solid after 20, 30 and 120 min heating. For a typical, the samples of H-BNO collected after reacting for 20 min were dried at 80 o C for 24 h in a common oven, and then a calcination process at 600 o C for 3 h in air produced HM-Nb 2 O 5. Synthesis of B-Nb 2 O 5 particles: For comparison, bulk Nb 2 O 5 particles (B-Nb 2 O 5 ) were prepared by direct hydrolysis of niobium (Ⅴ) chloride with water. Typically, 0.27 g of NbCl 5 was dissolved in 35 ml anhydrous ethanol, and then 5 ml deionized water was injected directly. The white precipitation formed immediately and was transformed to B-Nb 2 O 5 by the same calcination process. Synthesis of HM-TiO 2, HM-Ti-Nb, HM-Nb-Mn, HM-Nb-Co nanopheres: Similar to the preparation of HM-Nb 2 O 5, different hollow metal oxides could be easily prepared by simply change the reactant from NbCl 5 into TiCl 4 or multi-metal salts of TiCl 4 /NbCl 5, NbCl 5 /MnCl 2, NbCl 5 /CoCl 2. Using the synthesis of HM-Nb-Mn as a typical case, a mixed metal source of 0.27 g NbCl 5 and g MnCl 2 4H 2 O were used as reactants, and the precursor for hollow bi-metal oxide of Nb-Mn-O was successfully prepared after 120 min reaction at 80 o C. The same water washing followed by a same calcination can produced hollow and mesoporous Nb-Mn bi-metal oxide (HM-Nb-Mn). The synthesis process of other metal oxides were almost exactly the same, except different metal sources. Characterization The morphology and microstructure of the samples were characterized using a field emission scanning electron microscope (SEM, JEOL 6701F) at an acceleration voltage of 10.0 kv, and a transmission electron microscope (TEM, JEOL-2100F) at an acceleration voltage of 200 kv. High-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray (EDX) elemental mapping images were collected on a JEOL-2100F microscope. The crystal structures of the samples were identified by S1

2 X-ray diffraction (XRD) patterns on a Bruker D8 Advance diffractometer with Cu Kα radiation (λ = Å). The analysis of the surface area and pore parameters of the samples was performed using the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods on a Micrometrics ASAP 2010 apparatus. X-ray photoelectron spectroscopy (XPS) analysis was tested on a Thermo Scientific ESCALab 250Xi spectrometer with monochromic Al Kα radiation. FTIR spectras were recorded by BRUKER IR microscope (TENSOR-27). Thermogravimetric analysis (TGA) was taken on SIMULTANEOUS DTA-TG APPARTUS (DTG-60H, SHIMADZU) in the air. Electrochemical Tests The Nb 2 O 5 -based electrodes were prepared by mixing the active materials, super-p carbon and polyvinylidene fluoride (PVDF) binder at a weight ratio of 7:2:1 in N-methyl-2-pyrrolidinone (NMP). And then the homogeneous mixture was cast onto a pure Cu foil, dried at 80 o C in a vacuum oven, and cutting into circular electrodes with the mass loading in the range of mg cm -2. The electrochemical performances of the samples were investigated using CR2032 coin cells for half-cell tests. The half-cell tests were carried out using Nb 2 O 5 as cathode and Li metal as anode. All of the cells used Celgard polypropylene membrane as separator and a solution of 1 M LiPF 6 in EC/DMC/EMC (v/v/v, 1:1:1) as electrolyte, and assembled in an argon-filled glovebox. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were recorded on an AutoLab PGSTA302A electrochemical workstation. The galvanostatic charge and discharge (GCD) tests were carried out on a Land CT2001A battery test system. The working voltage window was set to V. Based on the theoretical capacity of Nb 2 O 5, the current density of 1 C is equal to 200 ma g -1. Figure S1. Curves of (a) XRD, (b) TGA, (c) FT-IR, and (d) EA for the initial precipitate of UNO. For FTIR of (c), the presence of absorption bands at 1717 cm 1 ( C=O stretching), 1395 and 1250 cm 1 (C(O) OH bending) revealed the UNO sample contain carboxylic acid, which originates from oxalic acid. Meanwhile, the peaks at 3450 cm 1 ( NH amide stretching), 3353 and 3236 cm 1 ( NH 2 stretching), 1641 cm 1 ( C=O amide stretching), 1562 cm 1 ( NH bending) and 1149 cm 1 (C N stretching) were associated with the nitrogen-hydrogen bonds attributable to amides. S2

3 Figure S2. Photographs of the initial precipitate of UNO which was ethanol-insoluble (a) and watersoluble (b). Figure S3. Photographs of the precipitate after 20 min's reaction which was not only ethanol-insoluble (a) but also water-insoluble (b). S3

4 Figure S4. TEM images of the niobium precursor collected at different reaction time followed by water washing: (a) 30 min, (c) 120 min. Figure S5. (a) Nitrogen adsorption desorption isotherm and (b) the pore size distribution of HM-Nb 2 O 5 product. S4

5 Figure S6. TEM images of the formed Nb 2 O 5 product calcined at different temperature for 3 h: (a) 500 o C, (b) 600 o C, (c) 700 o C. (d) XRD results of the formed Nb 2 O 5 products. Taking a lower calcination process at 500 o C for 3 h in air produced a hollow but almost no mesopores Nb 2 O 5. When the temperature climbed from 600 o C to 700 o C, the crystal particles in the shell grew bigger and the size of mesopores became smaller. Figure S7. The comparison of (a) FT-IR spectra and (b) element content of the inner part washed out form the sample collected after 20 minute s reaction and the initial precipitate of UNO. S5

6 Figure S8. Curves of (a) TGA and (b) element content for the precipitate of BNO collected at a reaction time of 20 min followed by water washing. Figure S9. (a) TEM image of the corresponding hollow niobium precursor prepared at the reaction temperature of 65 oc for 20 min. (b) Photographs of the precipitate (left) prepared at the reaction temperature of 50 oc for 20 min which was water-soluble (right). Figure S10. TEM images of the niobium precursor prepared in different solvents of (a) methanol and (b) isopropanol. Methanol and isopropanol were similar to ethanol, and also can be used as the solvents to prepare hollow nanospheres. But other solvents such as acetone or THF were not suitable as the reaction solution, because urea niobium oxalate couldn't precipitate in them. S6

7 Figure S11. SEM images for the prepared samples of (a) HM-TiO 2, (b) HM-Nb-Mn, (c) Ti-Nb and (d) Nb-Co respectively. Figure S12. TEM and elemental mapping images with EDX spectra for the prepared samples of (a) HM-TiO 2, (b) HM-Nb-Mn, respectively. S7

8 Figure S13. TEM and elemental mapping images with EDX spectra for the precursor samples of (a) Ti- Nb, (b) Nb-Co, respectively. Figure S14. TEM images and EDX spectra for the precursor samples of Ti-Nb with different raw ratio: (a) Ti/Nb=1:1, (b) Ti/Nb=2:1, respectively. S8

9 Figure S15. Photographs of (a) HM-TiO 2, (b) HM-Ti-Nb, (c) HM-Nb-Mn, (d) HM-Nb-Co after calcination. Figure S16. TEM images of the samples prepared by direct hydrolysis of NbCl 5 : (a) before calcination, (b) after calcination (B-Nb 2 O 5 ). S9

10 Figure S17. (a) Galvanostatic charge-discharge curves for B-Nb 2 O 5 electrodes at various rates (1 to 50 C). (b) CV curves of B-Nb 2 O 5 electrodes at a scan rate of 0.2 to 2 mvs -1. Figure S18. A comparison of our result to those recently published ones. 1-7 REFERENCES (1) Sun, H.; Mei, L.; Liang, J.; Zhao, Z.; Lee, C.; Fei, H.; Ding, M.; Lau, J.; Li, M.; Wang, C.; Xu, X.; Hao, G.; Papandrea, B.; Shakir, I.; Dunn, B.; Huang, Y.; Duan, X. Science 2017, 356, 599. (2) Lim, E.; Jo, C.; Kim, H.; Kim, M.-H.; Mun, Y.; Chun, J.; Ye, Y.; Hwang, J.; Ha, K.-S.; Roh, K. C.; Kang, K.; Yoon, S.; Lee, J. ACS Nano 2015, 9, (3) Kong, L.; Zhang, C.; Wang, J.; Qiao, W.; Ling, L.; Long, D. Sci. Rep. 2016, 6, (4) Zhang, J.; Chen, H.; Sun, X.; Kang, X.; Zhang, Y.; Xu, C.; Zhang, Y. J. Electrochem. Soc. 2017, 164, A820. (5) Liu, Y.; Lin, L.; Zhang, W.; Wei, M. Sci. Rep. 2017, 7, (6) Lou, S.; Cheng, X.; Wang, L.; Gao, J.; Li, Q.; Ma, Y.; Gao, Y.; Zuo, P.; Du, C.; Yin, G. J. Power Sources 2017, 361, 80. (7) Lim, E.; Kim, H.; Jo, C.; Chun, J.; Ku, K.; Kim, S.; Lee, H. I.; Nam, I.-S.; Yoon, S.; Kang, K.; Lee, J. ACS Nano 2014, 8, S10