Creating 3D Hierarchical Carbon Architectures with Micro-, Meso- and Macropores via a Simple Self-Blowing Strategy for

Transcription

1 Supporting Information Creating 3D Hierarchical Carbon Architectures with Micro-, Meso- and Macropores via a Simple Self-Blowing Strategy for Flow-Through Deionization Capacitor Shanshan Zhao, Tingting Yan, Hui Wang, Jianping Zhang, Liyi Shi, Dengsong Zhang* Research Center of Nano Science and Technology, Shanghai University, Shanghai , China. Fax: ; dszhang@shu.edu.cn S-1

2 Experimental section Characterization The thermogravimetry (TG) was tested on PE Paris 1 TGA instrument under the atmosphere of N 2 with a heating rate of 10 o C/min from 25 o C to 800 o C. The N 2 adsorption-desorption mearsurments were tested at Autosorb-IQ2 (Quantachrome Corporation). The specific surface area and pore volume was calculated using Brunauer-Emmett-Teller (BET) method. The pore size distribution was analysed by the Quenched-solid Density Functional Theory (QSDFT) model. The macropore size distribution was obtained from Hg porosimetry analysis (AutoPore IV 9510). The morphologies were observed by field emission scanning electron microscopy (SEM, JEOL JEM-700F), transmission electron microscopy (TEM, JEOL JEM-200CX) and high resolution transmission electron microscopy (HRTEM, JEOL JEM-2010F). The X-ray diffraction (XRD) measurements were tested in Rigaku D/MAX-RB X-ray diffractometer, which use Cu Kα radiation (40 KW, 20 ma) and a secondary beam graphite monochromator. The Raman spectra were measured on a spectrometer (JY H800UV) at room temperature. For excitation, the 633 nm line from a HeNe ion laser (Spectra Physics) was focused on the sample under the microscope with an analyzing spot was about 1 µm. The dynamic contact angle analysis were tested on a drop shape analysis system (Krüss, DSA100) using the same electrodes with the electrochemical tests. Electrochemical measurements The electrochemical performance of the electrodes was evaluated by cyclic voltammetry (CV) using a CHI 660D (Shanghai Chenhua, China). The specific capacitances were obtained from the formular (S1): C ( IdV) 2 Vm = υ / (S1) S-2

3 In which C is the specific capacitance, I is the current density, dv is the voltage window, v is the scan rate and the m is the mass of the electrode materials. Electrochemical impedance spectroscopy (EIS) tests were carried out by using CHI 660D also. The galvanostatic charge-discharge (GC) measurements were tested on the automatic LAND battery test instrument (Wuhan Land Electronic Co. Ltd) to measure the charge-discharge performance. All these tests were carried out in a three-electrode system in a 0.5 M NaCl solution. S-3

4 Additional results and discussions Figure S1. TG and DTG curves of KHCO 3 without or with cation exchange resin. Figure S1 displays the TG curves of KHCO 3 without or with cation exchange resin. For KHCO 3, the weight loss mainly appears between ~110 o C and 220 o C, and a sharp peak centred at ~200 o C can be seen from DTG curve, corresponding to the decomposition of KHCO 3, which can be presented by equation S2: 2KHCO3 K2CO3+ CO2+ H2O (S2) For the mixture of KHCO 3 and resin, the initial weight between 100 o C and 200 o C was caused by the carbonization of the resin and decomposition of KHCO 3. The weight loss between 400 o C to 500 o C was mainly because of the activation process, which can be presented by equations of S3-S6 1-4 : K + (S3) 2CO3 K2O CO2 K2 CO3+ 2C 2K+ 3CO (S4) K 2 O+ C 2K+ CO (S5) CO 2 + C 2CO (S6) S-4

5 Due to the series reactions listed above, the 3DHCA was activated sufficiently. The typical yield of the 3DHCA is around 10%. It is noteworthy that the 3DHCA is very lightweight and has an ultra-low bulk density and thus has a huge volume due to its high specific surface area. S-5

6 Figure S2. (a) N 2 adsorption desorption isotherms and (b) pore size distribution of the samples. Figure S2 displays the N 2 adsorption-desorption isotherms of all the samples. The control of specific surface area was studied by first adjusting the calcination temperature. At the fixed ratio of 4 of KHCO 3 to the resin, when the calcination temperature increases from 600 o C to 800 o C, the specific surface area increased from 985 m 2 g -1 to 2061 m 2 g -1 correspondingly, suggesting a higher calcination temperature leads to a higher specific surface area. This can be explained that at 800 o C, the reactions (equation S2-S6) are complete, while at 600 and 700 o C, the reactions cannot take place sufficiently. The control of specific surface area was also studied by adjusting the ratio of KHCO 3 to the resin. At the certain calcination temperature of 800 o C, when the ratio increases from 2 to 4, the specific surface area first increased from 1933 m 2 g -1 to 2061 m 2 g -1. This result can be attributed to that at low ratio of 1:2, the reactions cannot occur completely. When the ratio of KHCO 3 to the resin increase from 4 to 8, the specific surface area decrease from 2061 m 2 g -1 to 1670 m 2 g -1, and the trend is nearly linear (Figure S3). The decrease of the specific surface area with the increase of the ratio can be explained that at high ratio of 1:5, 1:6 and 1:8, S-6

7 the corrosive effect is too serious. Therefore, appropriate ratio is very important to enlarge the specific surface area. Figure S3. The specific surface area of the 3DHCA/x-800 with the ratio of KHCO 3 to resin. S-7

8 Figure S4. (a, b) SEM images of the DC; (c, d) SEM images of the 3DHCA at different magnifications Figure S4a and S4b present the SEM images of the DC. It is obvious that the DC has a bulk morphology and it has no pores. Figure S4c and S4d show the SEM images of the 3DHCA under different magnifications. It can be seen that the 3DHCA has 3D framework with interconnected channels and a large number of macropores. The strong contrast between the 3DHCA and DC suggests the activation method is very effective. S-8

9 Figure S5. CV curves of the (a) 3DHCA electrode (b) DC electrode at 1-40 mv s -1 in a 0.5 M NaCl solution; (c) CV curves of the 3DHCA electrode at 5 mv s -1 in different NaCl solutions. Figure S5a and S5b displays the CV curves of the 3DHCA and DC electrodes at different scan rates in a 0.5 M NaCl solution. At low scan rate of 1 mv s -1, the shape of the curve is relatively rectangular. When the scan rate was increased, the shape of the CV curves shows an increased distortion from the rectangular shape to the leaf-like shape. The deviation of shape is because of the inherent inner resistance and the polarization effect of the electrodes at high scan rates 5. For all the scan rates, the area of the CV curves of the 3DHCA electrode is larger than that of DC electrode, suggesting the 3DHCA electrode has higher specific capacitance. Figure S5c shows the CV curves of the 3DHCA electrode in different concentration of NaCl aqueous solution. As the concentration of NaCl increases, the specific capacitance increases correspondingly. The reason is S-9

10 that at higher concentration, more salt ions can be absorbed in the EDLC because of the improved accumulation of salt ions on the surface of the electrode. In addition, higher concentration always leads to a better conductivity due to the large amount of Na + and Cl - 6. S-10

11 Figure S6. CV curves of the 3DHCA electrode at 10 mv s -1 in 100, 300 and 500 mg/l NaCl solutions with a potential window of 0 to 1.2 V. Figure S6 displays the CV curves of the 3DHCA electrode at 10 mv s -1 in 100, 300 and 500 mg L -1 NaCl solutions with a potential window of 0 to 1.2 V (the same conditions as the deionization experiments). Obviously, for all the curves, no reduction or oxidation peak can be observed, suggesting the electrode has ideal capacitive behaviors in a potential window of V. However, the curves are deviation from rectangular shape. This can be explained that the concentration of NaCl solutions are very low, which lead to a low ion conductivity and large resistance. S-11

12 Table S1 Comparison of SAC of various carbon electrode materials from the literature Electrode material Cell voltage (V) NaCl concentration (mg L -1 ) SAC (mg g -1 ) Ref. Carbon nanorods Activated carbon Carbon nanotubes Carbon nanotubes/graphene 1.2 ~ Graphene aerogel Graphene oxide/porous carbon nanofibers Activated carbon/polyaniline ~ Porous carbon spheres Nitrogen-doped graphene Nitrogen-doped porous carbon spheres Mesoporous graphene 1.6 ~ Graphenic fibers Purified graphene 1.5 ~ Porous carbon Nitrogen-doped carbon nanorods Activated carbon treated by sulfuric acid ~ Porous carbon polyhedra Porous carbon nanofibers/dimethyl sulfone Activated carbon nanofibers/carbon nanotubes Three-Dimensional Graphene Architecture with Nanopores DHCA This work 3DHCA This work 3DHCA This work S-12

13 Table S2 A comparison of the charge efficiency of electrode materials from the literature Electrode materials Cell voltage (V) Initial NaCl concentration (mg L -1 ) Charge efficiency Ref. Three-Dimensional Graphene Architecture with Nanopores ~ Graphene sponge Nitrogen-doped graphene 1.2 ~ Porous carbon spheres Graphene-like carbon nanosheets Reduced graphene oxide/activated carbon composites Carbon nanotubes/graphene 1.2 ~ DHCA This work 3DHCA This work 3DHCA This work References (1) Foo, K. Y.; Hameed, B. H., Utilization of Rice Husks as a Feedstock for Preparation of Activated Carbon by Microwave Induced KOH and K 2 CO 3 Activation. Bioresour. Technol. 2011, 102, (2) Deng, J.; Xiong, T.; Xu, F.; Li, M.; Han, C.; Gong, Y.; Wang, H.; Wang, Y., Inspired by Bread Leavening: One-Pot Synthesis of Hierarchically Porous Carbon for Supercapacitors. Green Chem. 2015, 17, (3) Foo, K. Y.; Hameed, B. H., Porous Structure and Adsorptive Properties of Pineapple Peel Based Activated Carbons Prepared via Microwave Assisted KOH and K 2 CO 3 Activation. Microporous Mesoporous Mater. 2012, 148, S-13

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