Supporting Information. Nanosheets with Selenium Vacancies for Supercapacitor

Transcription

1 Supporting Information Plasma-Assisted Synthesis of NiSe 2 Ultrathin Porous Nanosheets with Selenium Vacancies for Supercapacitor Ailiu Chang,, Chao Zhang,, Yu Yu,, Yifu Yu*,,, and Bin Zhang*,, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Department of Chemistry, School of Science, Tianjin University, Tianjin , China Collaborative Innovation Center of Chemical Science and Engineering, Tianjin , China Tianjin International Joint Research Center of Surface Technology for Energy Storage Materials, Tianjin Normal University, Tianjin , China * bzhang@tju.edu.cn (B.Z.) * yyu@tju.edu.cn (Y.Y.) S-1

2 1. Experimental Section. 1.1 Chemicals. Nickel oxalate (NiC 2 O 4 4H 2 O), selenium (Se), benzyl alcohol, butylamine, nickel nitrate (Ni(NO 3 ) 2 6H 2 O), sodium hydroxide (NaOH) and ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) were purchased from Aladdin Ltd. (Shanghai, China). All chemicals are analytical grade and used as received without further purification. 1.2 Synthesis of lamellar NiSe 2 -butylamine hybrid precursors. The NiSe 2 -butylamine precursors were synthesized according to the previous report. 1 First, 0.5 mmol NiC 2 O 4 4H 2 O and 1 mmol Se power were added into 27 ml of benzyl alcohol with ultra-sonication for 15 minutes. Then, the mixture was placed into an ice water bath and 8 ml butylamine was dropwise added into the solution. After stirring for 30 minutes, the resulting solution was transferred into a 50 ml Teflon-lined stainless steel autoclave and heated at 180 C for 12 h. After naturally cooling down to room temperature, the black precipitates were collected by centrifugation, and washed with absolute ethanol for three times. Finally, the products of lamellar NiSe 2 -butylamine hybrid precursors were obtained after drying in a vacuum oven at 60 C for 12 h. 1.3 Synthesis of NiSe 2 ultrathin porous nanosheets with selenium vacancies (NiSe 2 PNS vac ). The as-prepared lamellar NiSe 2 -butylamine precursors were placed onto a quartz boat and inserted into the tube furnace. Then the chamber of tube furnace was evacuated. Once the pressure was below 10 Pa, the chamber was purged with Ar gas at a flow rate of 200 ml min -1 for 10 min. After that, the pressure was S-2

3 confined to 70 Pa and Ar plasma (commercial MHz RF source) was ignited with power of 300 W for 20 min. Finally, the products of NiSe 2 PNS vac were obtained after washing with absolute ethanol and drying under vacuum at 60 C for 12 h. 1.4 Synthesis of NiSe 2 nanosheets (NiSe 2 NS). The NiSe 2 NS were obtained according to the previous report by sonication exfoliation. 1 The NiSe 2 -butylamine precursors were dispersed into ethanol and sonicated for 24 h. The resultant dispersions were centrifuged at 2000 r.p.m. for 10 min to precipitate non-exfoliated component. Then the supernatant is re-centrifuged at r.p.m. for 10 min to precipitate exfoliated NiSe 2 NS. Finally, the products of NiSe 2 NS were obtained after washing with ethanol and drying under vacuum at 60 C for 12 h. 1.5 Synthesis of NiSe 2 particles (NiSe 2 Particle). In a typical procedure, 2 8 mmol selenium powder was dissolved in 40 ml 2.5 mol/l NaOH aqueous solution. 4 mmol Ni(NO 3 ) 2 6H 2 O and 2 mmol EDTA-2Na were dissolved in 20 ml deionized water. The two solutions were mixed with strong stirring for 10 min. Then, the resulting solution was transferred into a 100 ml Teflon-lined autoclave and heated at 200 C for 18 h. The black precipitates were collected and washed with water and ethanol, and later dried in vacuum oven at 60 C for 12 h. 2. Characterization. The scanning electron microscopy (SEM) images were taken with a Hitachi S-4800 scanning electron microscope. The X-ray diffraction (XRD) patterns were carried out with a Panalytical X'Pert Pro diffraction system with a Cu Kα source (λ = Å). The XRD samples were prepared by randomly arranging the sample powders on the sample disk. The transmission electron microscopy (TEM), S-3

4 high resolution transmission electron microscopy (HRTEM) images, and elemental distribution mapping images were carried out with a JEOL JEM-2100F microscope and high-angle annular dark field transmission electron microscopy (HAADF-STEM) images were carried out on a JEM ARM200F. The thickness of nanosheets was determined by atomic force microscopy (AFM) (Bruker multimode 8). Fourier transform infrared spectroscopy (FT-IR) spectrum was carried out with a MAGNA1IR 750 (Nicolet Instrument Co) FTIR spectrometer. The electron paramagnetic resonance (EPR) spectra were recorded on a Bruker EMX-8 spectrometer operated at 9.5 GHz 100 K. The X-ray photoelectron spectroscopy (XPS) was recorded on Perkin Elmer PHI 1600 Versa Probe (Al Kα). All the peaks are calibrated with C 1s spectrum at binding energy of ev. 3. Fabrication of the working electrode and electrochemical measurements. To prepare working electrode, the catalyst, carbon black and polytetrafluoroethylene (PTFE) were mixed with a mass ratio of 80:10:10, and dispersed in ethanol by ultra-sonication for 30 min. The slurry was coated on a nickel foam (1 1 cm 2 ) current collector and then dried in an vacuum oven at 60 for 6 h. Finally, the working electrode was obtained after pressing nickel foam at 10 MPa for 30 s. The mass of the catalyst loading on the nickel foam was about 1 mg. The electrochemical measurements were carried out in a conventional three-electrode electrolytic cell in a 1.0 M KOH aqueous solution by using a CHI-660D electrochemical workstation. Hg/HgO electrode was used as the reference electrode and a platinum foil was used as the counter electrode. Based on the cyclic voltammogram (CV) curves, the volumetric S-4

5 capacitance (C V ) of the electrodes was calculated according to the following equation (1): V IdV V0 C V = (1) mv( V V ) 2 0 where C (F g -1 ) refers to the specific capacitance; m (g) is the mass of the active material, v (V s -1 ) is the scan rate; (V 0 -V) is the potential range, and I(A) is the CV current. Based on the discharge curves, the mass specific capacitance (sometime also called grevimetric specific capacitance) (C S ) of the electrodes was calculated according to following equation (2): I t C S = (2) m( V V ) 0 where C (F g -1 ) refers to the specific capacitance; m (g) is the mass of the active material; Δt is he discharge time; (V 0 -V) is the potential range in the three-electrode system. S-5

6 4. Results and Discussion. Figure S1. (a) SEM image and (b) XRD pattern of lamellar NiSe 2 -butylamine hybrid precursors. The SEM image (Figure S1a) showed that the NiSe 2 -butylamine hybrid precursors displayed a lamellar two-dimensional (2D) morphology. As shown in the low angle range of XRD patterns in Figure S1b, the diffraction peak of NiSe 2 -butylamine hybrid precursors at ~6.62 o was observed, indicating that the layers of butylamines and NiSe 2 were alternately arranged with a layer distance of 1.39 nm. 1 S-6

7 Figure S2. (a) TEM image and (b) HRTEM image of NiSe 2 NS. The TEM image showed the 2D morphology of nanosheets (Figure S2a). The HRTEM image (Figure S2b) revealed the lattice spacing of nm, which was consistent with (210) crystallographic plane of NiSe 2. These results demonstrated that the NiSe 2 -butylamine precursors were transformed into NiSe 2 NS after sonication treatment for 24 h. S-7

8 Figure S3. (a) SEM image and (b) XRD pattern of NiSe 2 particle. The SEM image and XRD pattern (Figure S3) confirmed the successful preparation of NiSe 2 particles according to the reported literature. S-8

9 Figure S4. FT-IR spectra of NiSe 2 -butylamine hybrid precursors, NiSe 2 PNS vac and NiSe 2 NS. The FT-IR adsorption peaks of organic group in NiSe 2 -butylamine hybrid precursors disappeared after exfoliation into NiSe 2 PNS vac and NiSe 2 NS by plasma and sonication, respectively. These results suggested that butylamine was totally removed from the precursors after the plasma and sonication treatment. Figure S5. The EDS spectrum and STEM-EDS mapping images of NiSe 2 PNS vac. S-9

10 Figure S6. (a) CV curves of NiSe 2 PNS vac at different scan rates from 5 to 50 mv s 1 measured between 0 and 0.7 V. (b) GCD curves of NiSe 2 PNS vac at different current densities from 3 to 20 A g -1. It can be clearly seen that all the CV curves were consisted of a pair of visible redox peaks for NiSe 2 PNS vac, relating to a phase transformation as described by Eq.S1 Eq.S3 (Figure S6a). With the increase of increment in the sweep rate from 5 to 50 mv s -1, the shapes of CV curves were maintained well and the peak current of NiSe 2 PNS vac, increased, showing promising potential for good capacitance. The GCD curves of NiSe 2 PNS vac electrode (Figure S6b) at different current densities were in good agreement with the CV curves (Figure S6a) and consistent well with previous reports. 3 NiSe 2 + H 2 O + 1/2O 2 Ni(OH) 2 + 2Se (3) Ni(OH) 2 + OH - NiOOH + H 2 O + e- (4) NiO + OH - NiOOH + H 2 O + e- (5) S-10

11 Figure S7. (a) CV curves of NiSe 2 NS at various scan rates from 5 to 50 mv s 1 measured between 0 and 0.7 V. (b) GCD curves of NiSe 2 NS at different current density from 3 to 20 A g -1. It can be clearly seen that all the CV curves were consisted of a pair of visible redox peaks for NiSe 2 NS, relating to a phase transformation as described by Eq.S1 Eq.S3 (Figure S7a). With the increase of increment in the sweep rate from 5 to 50 mv s -1, the shapes of CV curves were maintained well and the peak current of NiSe 2 NS, increased, showing promising potential for good capacitance. The GCD curves of NiSe 2 NS electrode (Figure S7b) at different current densities were in good agreement with the CV curves (Figure S7a) and consistent well with previous reports. 3 S-11

12 Figure S8.. (a) CV curves of NiSe 2 particle at various scan rates from 5 to 50 mv s 1 measured between 0 and 0.7 V. (b) GCD curves of NiSe 2 particle at different current density from 3 to 20 A g -1. It can be clearly seen that all the CV curves were consisted of a pair of visible redox peaks for NiSe 2 Particle, relating to a phase transformation as described by Eq.S1 Eq.S3 (Figure S8a). With the increase of increment in the sweep rate from 5 to 50 mv s -1, the shapes of CV curves were maintained well and the peak current of NiSe 2 Particle, increased, showing promising potential for good capacitance. The GCD curves of NiSe 2 Particle electrode (Figure S8b) at different current densities were in good agreement with the CV curves (Figure S8a) and consistent well with previous reports. 3 S-12

13 Table S1. Supercapacitor performance of the NiSe 2 in this study, compared with previous literatures. Catalyst Electrolyt e Current density (A g -1 ) Specific capacitance (F g -1 ) Ref. NiSe 2 PNS vac 1 M KOH This work NiSe 2 NS 1 M KOH This work hexapod-like NiSe 2 1 M KOH a 75 4 NiSe 2 hollow spheres 2 M KOH truncated cube NiSe 2 4 M KOH NiSe microspheres 2 M KOH Ni 0.85 Se 2 M KOH Ni-Co oxide nano-composit 6 M KOH NiCo 2 O 4 crystals 1 M KOH b NiCo 2 O 4 nanoplates 2 M KOH NiO nanoflower 2 M KOH Ni(OH) 2 /Ultrathin-gr aphite foam 6 M KOH Ni NiO core shell 1 M KOH c 96±32 14 a : The scanning rate is 2 mv s -1. b : The current density is 1 ma cm -2. c : The current density is 0.2 ma cm -2. S-13

14 Figure S9. (a) CV curves of NiSe 2 PNS vac before and after 1000 cycling times. (b) Cycling performance curve of the NiSe 2 PNS vac at a current density of 10 A g -1. S-14

15 Figure S10. (a) Cycling performance curves and GCD curves (inset in a) before and after cycling of the NiSe 2 NS at a current density of 10 A g -1. (b) The capacitive retentions of NiSe 2 NS during 1000 cycles. S-15

16 Figure S11. (a) Cycling performance curves and GCD curves (inset in a) before and after cycling of the NiSe 2 Particle at a current density of 10 A g -1. (b) The capacitive retentions of NiSe 2 particle during 1000 cycles. S-16

17 Table S2. Calculated electrochemical parameters for various working electrodes based on the proposed circuit. Catalyst R e (Ω) R ct (Ω) W(Ω) NiSe 2 PNS vac NiSe 2 NS NiSe 2 Particle REFERENCES (1) Chen, S.; Kang, Z.; Hu, X.; Zhang, X.; Wang, H.; Xie, J.; Zheng, X.; Yan, W.; Pan, B.; Xie, Y. Delocalized Spin States in 2D Atomic Layers Realizing Enhanced Electrocatalytic Oxygen Evolution. Adv. Mater. 2017, 29, (2) Ou, X.; Li, J.; Zheng, F.; Wu, P.; Pan, Q.; Xiong, X.; Yang, C.; Liu, M. In Situ X-ray Diffraction Characterization of NiSe 2 as a Promising Anode Material for Sodium Ion Batteries. J. Power Sources 2017, 343, (3) Mani, S.; Ramaraj, S.; Chen, S.-M.; Dinesh, B.; Chen, T.-W. Two-dimensional Metal Chalcogenides Analogous NiSe 2 Nanosheets and Its Efficient Electrocatalytic Performance towards Glucose Sensing. J. Colloid Inter. Sci. 2017, 507, (4) Arul, N. S.; Han, J. I. Facile Hydrothermal Synthesis of Hexapod-like Two Dimensional Dichalcogenide NiSe 2 for Supercapacitor. Mater. Lett. 2016, 181, S-17

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