Energy-saving Synthesis of MOF-Derived Hierarchical and hollow. electrode materials

Transcription

1 Supporting Information Energy-saving Synthesis of MOF-Derived Hierarchical and hollow Co(VO 3 ) 2 -Co(OH) 2 Composite Leaf Arrays for Supercapacitor electrode materials Yingxi Zhang, a,b Hao Chen, b,c, * Cao Guan, c, * Yatao Wu, b Chunhai Yang, d Zhehong Shen, b, * and Qichao Zou a, * a College of Chemistry and Chemical Engineering, Hubei University, Wuhan , PR China b School of Engineering, Zhejiang A&F University, Hangzhou , PR China. c Department of Materials Science and Engineering, National University of Singapore, Singapore d School of Chemistry & Environment Engineering, Hubei University for Nationalities, Enshi, , PR China Corresponding author. haochen10@fudan.edu.cn (H. Chen); msegc@nus.edu.sg (C. Guan); zhehong.shen@vip.163.com (Z. Shen); qichaozou58@126.com (Q. Zou). S-1

2 Experimental Section Fabrication of The cobalt-based metal-organic framework supported on carbon cloth was prepared according to our previous report. 1 In a typical process, the commercial CC was pre-washed successively with acetone, deionized water, and absolute ethanol, each for 15 min, to ensure a clean surface. An aqueous solution contains 2- methylimidazole (2-MIM) (40 ml, 0.8 M) was quickly added into the aqueous solution of Co(NO 3 ) 2 6H 2 O (40 ml, 0.1 M), then six pieces of clean CC substrate ( cm 3, the upper side was protected by polytetrafluoroethylene tape) were immersed into this mixture for 2 h to grow Co-MOF under room temperature. After the reaction, the as-obtained Co-MOF@CC was then taken out, cleaned with deionized water and then moved to the next step immediately. Preparation of Co-V@CC: Three pieces of as-fabricated Co-MOF@CC were immersed into an aqueous solution of NaVO 3 (80 ml, 6 mm) and kept stationary to allow an in-situ conversion from Co-MOF to Co(VO 3 ) 2 -Co(OH) 2 composite (Co-V) on the surface of CC substrate. After a reaction of 150 min under room temperature (near 25 o C), the resulting product was washed with deionized water and absolute ethanol for three times, respectively, and then dried at 60 o C to provide a Co-V-150@CC sample. Similarly, the Co-V-x@CC samples obtained with different reaction time (x) were also fabricated using the similar procedure. To investigate the influences of temperature and concentration of the NaVO 3 solution on the morphology of resulting products, the Co-V composites were prepared by changing the temperature or concentration via a similar method, and keeping other parameters fixed. In addition, according to a previous report, 2 the Co(OH) was fabricated by heating the Co-MOF@CC in a mixed solvent of ethanol (20 ml) and deionized water (5 ml) at 85 o C for 30 min, followed by washing and drying the S-2

3 product via the similar process. The loading area of active materials on CC was about 2 cm 2 for all electrodes. Characterization. The morphologies were observed by scanning electron microscopy (SEM, SU8010, Hitachi). The transmission electron microscope (TEM) images and Energy-dispersive X-ray spectroscopy (EDXS) were obtained on a FEI Tecnai G2 F30 S-TWIN field emission microscope. The crystalline structure was characterized by X-ray diffraction (XRD) patterns recorded in a Rigaku Smartlab diffractometer with D/teX Ultra 250 HE detector. X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250XI) measurements were employed to investigate the elemental compositions of the samples. Raman spectra were carried out on a Raman spectrometer (HORIBA LabRam HR 800). The nitrogen adsorption-desorption isotherm of the sample was measured on a Quantachrome QuadraSorb Station 3 instrument at 77 K. Electrochemical measurement. The electrochemical properties of the as-obtained all electrodes were investigated under a three-electrode cell configuration at 25 o C in 1 M LiOH. The CC supported samples acted as the working electrodes, and were soaked in a 1 M LiOH solution and degassed in a vacuum for 1 h before the electrochemical test. Platinum foil and a saturated calomel electrode (SCE) were used as the counter and reference electrodes, respectively. The cyclic voltammetry (CV) measurements were conducted on a CHI 760E electrochemical workstation (Shanghai CH Instrument Company, China). The galvanostatic charge-discharge tests were carried out on a Land test system (LAND CT2001A, China). S-3

4 Figure S1. (a) A low magnification SEM image shows the uniform growth of Co-V-150 on carbon cloth. (b) The red arrows in a SEM image show the hollow structure of Co-V-150. S-4

5 Figure S2. (a) N 2 (77 K) adsorption/desorption isotherm and (b) BJH pore size distribution curve of as-synthesized of Co-V-150 supported on CC. Figure S3. TEM images of Co-V-150 at two different magnifications. S-5

6 Figure S4. SEM images of samples at different magnifications: (a, b) Co-V-90, (c, d) Co-V-120, (e, f) Co-V-180, (g, h) Co-V-210. S-6

7 Figure S5. (a-c) SEM images of Co-MOF derived Co(OH) 2. (d) Charge-discharge curves of the as-prepared Co(OH) 2 electrode. S-7

8 Figure S6. The charge-discharge curves of electrodes at different current densities: (a) Co-V-90, (b) Co-V-120, (c) Co-V-180, (d) Co-V-210. S-8

9 Figure S7. Comparison of SEM images of Co-V-150 before and after charge-discharge cycles: (a, b) before cycling test, (c, d) after cycling test. S-9

10 Figure S8. Comparison of SEM images of Co-V composites prepared at 25 o C in (a, b) 4 mm and (c, d) 8 mm NaVO 3 solution. Comparison of SEM images of Co-V composites prepared in 6 mm NaVO 3 solution at (e, f) 5 o C and (g, h) 35 o C. (Reaction time: 150 min). S-10

11 Based on Figure S8, it can be found that both the concentration and temperature of NaVO 3 solution can affect the morphology of the as-prepared Co(VO 3 ) 2 -Co(OH) 2 leaf arrays. Because the co-growth of Co(OH) 2 nanosheets and Co(VO 3 ) 2 nanoparticles resulted in the formation of irregular sheet-like structure on the leaf surface, this irregular structure exhibited a more visible sheet-like feature when a lower NaVO 3 concentration was used (Figure S8a-b), due to a less growth of Co(VO 3 ) 2 nanoparticles. When the NaVO 3 concentration was relatively high, the amount of Co(VO 3 ) 2 nanoparticles increased, thus a more obvious paticle-like feature was observed on the leaf surface (Figure S8c-d). With regard to the effects of temperature, too low temperature (5 o C) was not conducive to the formation of hollow structure due to that the exchange reaction between VO 3 and the 2- MIM ligands of interior Co-MOF decelerated (Figure S8e-f). In contrast, the further exchange reaction between Co(OH) 2 and VO 3 accelerated at a relatively high temperature (35 o C), leading to the growth of more Co(VO 3 ) 2 nanoparticles on the leaf surface (Figure S8g-h). S-11

12 Table S1. Comparison of maximum C s and cycle stabilities of some reported similar materials and the present work. Electrodes based on materials C s Cycle stability Ref. Co(OH) 2 nanoflakes 387 F g 1 (1 ma cm 2 ) 92 % (10 ma cm 2, 2000 cycles) 3 Porous β-co(oh) F g 1 (1 A g 1 ) 93 % (1 A g 1, 500 cycles) 4 MOF derived Co(OH) 2 nanocubes 420 F g 1 (1 A g 1 ) 82 % (10 A g 1, 5000 cycles) 5 Flower-like Co(OH) F g 1 (1 A g 1 ) - 6 Co(OH) 2 nanocone arrays 562 F g 1 (2 A g 1 ) 88 % (2 A g 1, 3000 cycles) 7 MOF derived Co(OH) F g 1 (0.1 A g 1 ) 70 % (2 A g 1, 2000 cycles) 8 Porous Co(OH) 2 Nanoflake 609 F g 1 (5 mv s 1 ) 91 % (1 ma cm 2, 3000 cycles) 9 α-co(oh) 2 nanowire arrays 643 F g 1 (1 A g 1 ) - 10 β-co(oh) 2 disc-like nanostructures 737 F g 1 (10 mv s 1 ) 96 % (1 A g 1, 500 cycles) 11 Co(OH) 2 /TiO 2 nanotube 229 F g 1 (2 ma cm 2 ) 91 % (2 ma cm 2, 1000 cycles) 12 α-co(oh) 2 /Co 3 O 4 Flakes 583 F g 1 (1 A g 1 ) 88 % (1 A g 1, 1000 cycles) 13 Quasi-cuboidal CoV 2 O F g 1 (1 A g 1 ) 123 % (5 A g 1, cycles) 14 Co 3 V 2 O 8 nanoroses 371 F g 1 (0.5 A g 1 ) 90 % (4 A g 1, 7000 cycles) 15 Co 3 V 2 O 8 nanoparticles 505 F g 1 (0.625 A g 1 ) 93 % (1.25 A g 1, 1000 cycles) 16 Co 3 V 2 O 8 thin nanoplates 739 F g 1 (0.5 A g 1 ) 95 % (0.5 A g 1, 2000 cycles) 17 Co(VO 3 ) 2 -Co(OH) 2 leaf arrays 803 F g 1 (0.5 ma cm 2 ) 522 mf cm 2 (0.5 ma cm 2 ) 90 % (10 ma cm 2, cycles) This work Notes: MOF is metal-organic framework. Based on this table, the obtainable highest C s (522 mf cm 2 or 803 F g 1 at 0.5 ma cm 2 ) of our Co(VO 3 ) 2 -Co(OH) 2 leaf arrays is significantly higher than those of most similar active materials, including pure Co(OH) 2, pure cobalt vanadate, and Co(OH) 2 based composites. Such high capacitance performances are attributed to the unique structure features of the Co(VO 3 ) 2 -Co(OH) 2 composite leaf arrays we present here: (i) The hierarchical, hollow, and porous 3D structure can allow intimate electrolyte penetration and fast S-12

13 ion/mass transport, and shorten ion diffusion distance; (ii) The direct growth of active materials on the highly conductive CC current collector can ensure electron transport highway for fast reaction at high rates. Unlike our Co(VO 3 ) 2 -Co(OH) 2 leaf arrays, most previously reported similar materials only possess simple microstructures and/or were used as the powder-like active materials to produce electrodes. Therefore, their C s values are not impressive. In regard to cycling performances, 90% of the initial capacitance can well retained for our Co(VO 3 ) 2 -Co(OH) 2 electrode after CD cycles of charge discharge at 10 ma cm 2. This performance is more superior relative to some similar electrodes based on the above Table S1. The excellent cycling performance should benefit from the well preservation of hierarchical hollow+porous arrays of this electrode during the cycling test, except for a slight coalescence of nanostructured units. The retained hierarchical structure can still support good electrolyte access and electron transport. Moreover, our active materials were in-situ grown on the carbon cloth, thereby they wouldn t easily flake off from current collector like powder-like active materials. Thus, the capacitance output can be well maintained. S-13

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