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Facile synthesis of three-dimensional interconnected porous carbon derived from potassium alginate for high performance supercapacitor
Journal of Alloys and Compounds 803 (2019) 401e406
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Facile synthesis of three-dimensional interconnected porous carbon derived from potassium alginate for high performance supercapacitor Shuxian Sun, Bing Ding, Ruonan Liu, Xiaoliang Wu* Department of Chemistry and Chemical Engineering, College of Science, Northeast Forestry University, 26 Hexing Road, Harbin, 150040, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 April 2019 Received in revised form 16 June 2019 Accepted 17 June 2019 Available online 18 June 2019
Porous carbon obtained by the conventional two-step way (chemical activation after carbonization) is confronted with the problems of long time-consuming, high cost and undeveloped macropore structure. Herein, for the first time, we report a facile and scalable way for the construction of three-dimensional (3D) interconnected porous carbons (IPC) originated from potassium alginate by a self-activation process. Owing to the high surface area, 3D interconnected ion diffusion channel and massive oxygen functional groups, the optimized IPC-800 electrode displays a high specific capacity of 279 F g1 at 1 A g1, superior rate capability (200 F g1 at 50 A g1) and excellent electrochemical stability with 96.6% capacitance retention after 10000 cycles in 6 M KOH aqueous electrolyte. Moreover, the assembled IPC-800//IPC-800 symmetric supercapacitor shows an energy density of 16.9 Wh kg1 and good electrochemical stability in 1 M Na2SO4 aqueous electrolyte. These exciting results indicate a facile, economical and scalable method for the synthesis of porous carbon materials for high performance supercapacitors. © 2019 Elsevier B.V. All rights reserved.
Keywords: Self-activation Potassium alginate Supercapacitors Energy density
1. Introduction Recently, with the increasing demand for energy and environmental pollution increasingly serious, there is no denying that the demand for renewable energy storage devices has become evermore urgent [1,2]. As a new energy storage device, supercapacitors have received massive attentions owing to the high power density, good cycling stability, rapid charge/discharge rate and low maintenance cost [3e6]. Generally, according to energy storage mechanism, supercapacitors can be classified into two types: electrical double-layer capacitors (EDLCs) and pseudocapacitors. Due to the rapid reversible adsorption and desorption of electrolyte ions in the double layer, EDLCs have higher power density and better cycling stability than pseudocapacitors. Porous carbon materials have been widely used in EDLCs owing to their appealing properties, for example, high specific surface area, numerous raw materials, and excellent electrochemical stability [7e10]. The traditional method for the construction of porous carbon mainly via two steps: carbon precursors are firstly carbonized in inert gas and then followed by activation with activating agent (KOH, ZnCl2, etc). However, the production process is
* Corresponding author. E-mail address: [email protected] (X. Wu). https://doi.org/10.1016/j.jallcom.2019.06.212 0925-8388/© 2019 Elsevier B.V. All rights reserved.
complicated, time-consuming and these activating agents severely corrode equipment, which are serious obstacles to large-scale production [11,12]. Moreover, porous carbon prepared by conventional way is confronted with high ion-transport resistance and insufficient ion diffusion, which result in low specific capacity and poor rate characteristic [13]. Recently, three-dimensional (3D) interconnected porous carbon with large specific surface area, hierarchical pore structure is desirable for high-performance electrode materials of supercapacitors [14e17]. The 3D interconnected hierarchical porous framework can not only provide large specific surface area to store charges, but also shorten ion diffusion distance, which has drawn numerous concerns [14]. However, the construction of 3D interconnected hierarchical porous carbon usually needs the tempting method including massive time-consuming procedure with template preparation, template removal, and post-activation, which are serious obstacles to large-scale production [18e20]. Herein, for the first time, we report a facile and scalable way for the construction of 3D interconnected porous carbons (IPC) originated from potassium alginate by a self-activation process. Owing to the large surface area, 3D interconnected ion diffusion channel and massive oxygen functional groups, the optimized IPC-800 electrode displays a high specific capacity of 279 F g1 at 1 A g1, superior rate capability and excellent electrochemical stability with 96.6% capacitance retention after 10000 cycles. Moreover, the
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assembled IPC-800//IPC-800 symmetric supercapacitor shows an energy density of 16.9 Wh kg1 and excellent electrochemical stability.
2. Material and methods 2.1. Construction of materials 3 g potassium alginate was directly carbonized at various temperatures (700, 800, 900 C) for 2 h in N2 atmosphere. The products were bathed by dilute HCl solution and gently stirred for 12 h. After that, the obtained samples were filtered and washed with distill water and ethanol. At last, the samples were dried in a vacuum dryer. The obtained materials were denoted as IPC-x, which x represents the temperature of carbonization temperature. The prepared process was shown in Scheme 1.
2.2. Characterizations The microstructures of the obtained samples were conducted by scanning electron microscopy (SEM, JEOL JSM-7500F) and transmission electron microscopy (TEM, JEOL JEM2010). The crystal structure was characterized by X-ray diffraction (XRD). The X-ray photoelectron spectroscopy (XPS) measurement was studied with Thermo ESCALAB 250XI spectrometer. Nitrogen adsorption/ desorption curves were checked by Autosorb IQ. The pore characteristics of nitrogen adsorption/desorption were measured by BET method, and the pore size distribution was calculated by density functional theory (DFT). 2.3. Electrochemical measurements In a three-electrode system, the working electrodes are prepared as follows: acetylene black (20 wt%), active materials (75 wt %) and polytetrafluoroethylene (5 wt%) form paste in ethanol. Then
Scheme 1. Schematic diagram illustrating the construction of the IPC materials using potassium alginate as the precursor.
Fig. 1. (a, b) SEM images of IPC-800. (c) TEM image of IPC-800. (d) High resolution TEM image of IPC-800.
S. Sun et al. / Journal of Alloys and Compounds 803 (2019) 401e406
evenly spread on foam nickel and vacuum dry at 60 C overnight, the loading mass is about 3 mg cm2. By using platinum foil as counter electrode, active material coated with Ni foam as working electrode and the Hg/HgO electrode is selected as reference electrode for measurement in 6 M KOH aqueous electrolyte. The electrochemical performance of the synthesized carbon materials was also evaluated in symmetrical device using two-electrode system in 1 M Na2SO4 solution. All measurements were tested by electrochemical workstation (CHI 660E). The specific capacitance (C) of the three-electrode system is calculated by equation (1), and the specific capacitance, power density (P) and energy density (E) of the symmetrical device are calculated by the following equations: C ¼ (I Dt)/(m DV)
(1)
C ¼ (!I dV)/(n mV)
(2)
E ¼ 0.5CV2
(3)
P ¼ E/Dt
(4)
In formula (1), I denotes current density, m denotes the mass of active material in a single electrode, Dt denotes the discharge time, DV denotes potential window. In formula (2), (3) and (4), I stands current density, n represents the scan rate, m symbolizes the weight of the active materials of the two electrodes and Dt is the time of discharge, V is the voltage window.
403
3. Results and discussions The micromorphologies of the obtained materials were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As seen in Fig. 1a and b, the IPC-800 samples display 3D interconnected porous framework with massive macropores. TEM image further confirms its unique 3D highly interconnected porous framework, which can not only provide available large specific surface area to store charges, but also shorten ion diffusion distance. Moreover, the high resolution TEM image of the IPC-800 samples show a great deal of micropores in the surface of carbon framework, which is in favor of charge storage. The IPC samples obtained at other temperatures also display 3D interconnected porous structure (Figs. S1a and b). With the increase of carbonization temperature, partly carbon wall gradually fragments and pore size enlarge due to the high temperature is conducive to activation. The decomposition process of potassium alginate was checked through thermogravimetric analysis (TGA). As seen in Fig. 2a, the TGA curve exhibits two weight loss steps in the temperature regions of 200e500 C and 700e800 C, which are corresponding to the decomposition of organic moiety with simultaneously to the formation of potassium carbonate and further reaction of potassium oxide with carbon (K2O þ C / 2K þ CO) produced by decomposition of potassium carbonate (K2CO3 / K2O þ CO2), respectively. X-ray diffraction (XRD) analysis was adopted to research the crystalline characteristic of the IPC samples (Fig. 2b). All IPC
Fig. 2. (a) TGA curve of potassium alginate. (b) XRD curves of IPC-700, IPC-800 and IPC-900. (c) XPS survey spectrum of IPC-800. (d) C 1s high-resolution spectra of IPC-800.
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Fig. 3. (a) N2 adsorption/desorption isotherms of IPC-700, IPC-800, IPC-900. (b) Pore sizes distribution of IPC-700, IPC-800, IPC-900.
materials show two broad characteristic peaks at 22.5 and 43.6 , which are attributed to the (002) and (101) crystal planes of the carbon material, respectively. The weak and broaden diffraction peaks indicate that the IPC-800 materials have massive defects and disordered structure. The surface characteristics of the IPC-800 materials were conducted by X-ray photoelectron spectra (XPS). As seen in Fig. 2c, the O content of IPC-800 can reach 9.0 at%. As seen in Fig. 2d, the C1s peak can be divided into four individual peaks: CeC (284.8 eV), CeOH (285.2 eV), C]O (287.1 eV) and COOH (289.23 eV), respectively [19,21]. The porous characteristics of the obtained samples were further investigated by N2 adsorption/desorption isothermals. As seen in Fig. 3a, the IPC-800 samples show a combined characteristic of I/IV type adsorptionedesorption isothermal. Moreover, the adsorption capacity increased sharply at the relative pressure P/P0 from 0 to 0.3 can be found, indicating that the IPC-800 samples possess massive micropores. The detailed pore structure information is listed in Table 1. The IPC-800 samples show a high specific surface area of 1145.8 m2 g1 with a high pore volume up to 0.58 cm3 g1 calculated by the BrunauereEmmetteTeller (BET) way. The pore size distribution of the IPC-800 samples show massive micropores and suitable mespores (Fig. 3b). Owing to the large surface area, 3D interconnected ion diffusion channel and massive oxygen functional groups, the IPC-800 samples are expected to be an outstanding candidate for supercapacitors. The electrochemical properties of the as-obtained samples were firstly evaluated by cyclic voltammetry (CV) using a three-electrode system in 6 M KOH aqueous electrolyte. Fig. 4a presents the profiles of the obtained materials at various carbonization temperatures. All the samples show quasi-rectangular profile without any redox peaks, indicating a perfect capacitive characteristic. Evidently, the IPC-800 electrode presents the largest
area surrounded by CV curves corresponding to the highest specific capacitance. Moreover, even at a high scan rate of 500 mV s1 (Fig. 4b), the CV profile of the IPC-800 electrode still maintains superior quasi-rectangular in shape, indicating excellent rate performance. Fig. 4c presents the galvanostatic charge/discharge profiles of the IPC-800 electrode at various current densities. All curves exhibit isosceles triangular shapes, demonstrating an ideal capacitive characteristic. The specific capacitance of the IPC-800 electrode evaluated by the discharge curves is 279 F g1 at 1 A g1 (Fig. 4d), which is much higher than commercial activated carbon (YP-50), IPC-700 and IPC-900. Notably, the IPC-800 electrode shows a high capacity retention rate of 71.7% (200 F g1) at 50 A g1, demonstrating fast charge and discharge rate at high current density. As displayed in Fig. 4e, the IPC-800 electrode displays the superior cycling stability with capacitance retention of about 96.6% after 10000 cycles, demonstrating excellent electrochemical stabilization. Nyquist plots of the IPC-800 electrode are displayed in Fig. 4f. In the high frequency areas, the IPC-800 electrode displays a low equivalent series resistance of 0.55 U, confirming good conductivity. In the low frequency, the IPC-800 electrode displays a nearly vertical line, demonstrating fast electron transport. After 10000 cycles of CV tests, Nyquist plots of the IPC-800 electrode almost no change in shape, further indicating excellent electrochemical stability. To further demonstrate the excellent electrochemical capability of IPC-800, a symmetric supercapacitor according to the IPC-800 electrodes using a two-electrode system was assembled. As reported by literature, alkali metal sulfate aqueous solutions can achieve a wider voltage region than alkaline solutions, which is propitious to achieve high energy density [22]. Therefore, the IPC800//IPC-800 symmetric supercapacitor was conducted in 1 M Na2SO4 aqueous electrolyte. Fig. 5a displays the IPC-800//IPC-800
Table 1 Physical parameters of the as-prepared carbon materials. Samples
SBET (m2 g1)a
Smic(m2 g1)b
Sext(m2 g1)c
Vtotal (cm3 g1)d
D (nm)e
IPC-700 IPC-800 IPC-900
722.0 1145.8 1281.8
623.5 957.7 1006.4
98.5 188.1 275.4
0.3541 0.5759 0.7150
1.96 2.01 2.23
a b c d e
Specific surface area (SBET) was calculated with modified Brunauer-Emmett-Teller (BET) method. Micropore specific surface area (Vmic) was obtained from t-plot method. External pore volume (Sext) was obtained from t-plot method (Sext ¼ SBET - Smic). Total pore volume (Vtotal) was estimated from the adsorbed amount at a relative pressure of 0.99. Average pore diameter (D) was obtained from D ¼ 4Vtotal/SBET.
S. Sun et al. / Journal of Alloys and Compounds 803 (2019) 401e406
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Fig. 4. (a) CV curves of IPC-700, IPC-800 and IPC-900 at 50 mV s1. (b) CV curves of IPC-800 at different scan rates. (c) GCD curves of IPC-800 at different current densities. (d) Specific capacitance of YP-50, IPC-700, IPC-800 and IPC-900 at different current densities. (e) Electrochemical stability of IPC-800 at 100 mV s1 for 10000 cycles. (f) Nyquist plots of the IPC-800 electrode before and after 10000 cycles.
Fig. 5. (a) CV curves of the IPC-800//IPC-800 symmetrical supercapacitor in different operation voltages at 50 mv s1. (b) CV curves of the IPC-800//IPC-800 symmetrical supercapacitor at different scan rate from 50 to 200 mV s1. (c) Ragone plots of the IPC-800//IPC-800 symmetrical supercapacitor and previously reported carbon-based symmetrical supercapacitors. (d) Electrochemical stability of the IPC-800//IPC-800 symmetrical supercapacitor tested at 100 mV s1 for 10000 cycles.
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symmetric supercapacitor at different voltage ranges. Clearly, it can be seen that the stable voltage range for the IPC-800//IPC-800 symmetric supercapacitor was 0e1.6 V. Fig. 5b displays the CV profiles of the symmetric supercapacitor at various scan rates from 50 to 200 mV s1. All the profiles show rectangular-like shapes and even at 200 mV s1 without the obvious deformation, suggesting outstanding rate characteristics. Owing to the wide voltage region and large specific capacity, the IPC-800//IPC-800 symmetric supercapacitor shows an energy density of 16.9 Wh kg1 (Fig. 5c), higher than previously reported porous carbon symmetric supercapacitors in aqueous electrolyte [23e26]. As displayed in Fig. 5d, the IPC-800//IPC-800 symmetric supercapacitor displays a good cycling stability with capacity retention of about 97.0% after 10000 cycles, indicating good electrochemical stability. 4. Conclusion In summary, we report a facile and scalable way for the construction of 3D interconnected porous carbons originated from potassium alginate by a self-activation process. Owing to the large surface area, 3D interconnected ion diffusion channel and massive oxygen functional groups, the optimized IPC-800 electrode displays high specific capacity, superior rate feature and excellent cycling stability. Moreover, the assembled IPC-800//IPC-800 symmetric supercapacitor shows high energy density and excellent electrochemical stability. Conflicts of interest Authors declare no conflict of interests.
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
Acknowledgement [19]
All authors are very grateful for the financial support of the National Natural Science Foundation of China (51702043), Heilongjiang Postdoctoral Foundation (LBH-Z18008).
[20]
Appendix A. Supplementary data
[21]
Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.06.212.
[22]
References [1] C. Liu, F. Li, L. Ma, H. Cheng, Advanced materials for energy storage, Adv. Mater. 22 (2010) 28e62. [2] P. Simon, Y. Gogotsi, Capacitive energy storage in nanostructured carbon electrolyte systems, Acc. Chem. Res. 46 (2013) 1094e1103. [3] T.Y. Liu, F. Zhang, Y. Song, Y. Li, Revitalizing carbon supercapacitor electrodes with hierarchical porous structures, J. Mater. Chem. A 5 (2017) 17705e17733. [4] J.Y. Hwang, M. Li, M.F. El-Kady, R.B. Kaner, Next-generation activated carbon supercapacitors: a simple step in electrode processing leads to remarkable gains in energy density, Adv. Funct. Mater. 27 (2017) 1605745. [5] H. Jiang, P.S. Lee, C. Li, 3D carbon based nanostructures for advanced supercapacitors, Energy Environ. Sci. 6 (2013) 41e53. [6] X.L. Wu, L.L. Jiang, C.L. Long, T. Wei, Z.J. Fan, Dual support system ensuring
[23]
[24]
[25]
[26]
porous CoeAl hydroxide nanosheets with ultrahigh rate performance and high energy density for supercapacitors, Adv. Funct. Mater. 25 (2015) 1648e1655. B. Ding, D. Guo, Y.H. Wang, X.L. Wu, Z.J. Fan, Functionalized graphene nanosheets decorated on carbon nanotubes networks for high performance supercapacitors, J. Power Sources 398 (2018) 113e119. J.H. Cao, C.Y. Zhu, Y. Aoki, H. Habazaki, Starch-derived hierarchical porous carbon with controlled porosity for high performance supercapacitors, ACS Sustain. Chem. Eng. 6 (2018) 7292e7303. C. Liang, J. Bao, C. Li, H. Huang, C. Chen, Y. Lou, H. Lu, H. Lin, Z. Shi, S. Feng, Onedimensional hierarchically porous carbon from biomass with high capacitance as supercapacitor materials, Micropor. Mesopor. Mat. 251 (2017) 77e82. J.L. Zhang, W.F. Zhang, H. Zhang, J. Pang, G.P. Cao, M.F. Han, Y.S. Yang, A novel synthesis of hierarchical porous carbons from resol by potassium acetate activation for high performance supercapacitor electrodes, J. Alloy. Comp. 712 (2017) 76e81. S.H. Kang, B.N. Kim, I.G. Kim, Facile synthesis of porous carbon via self-activation of potassium acetate for high performance supercapacitor electrodes with excellent cyclic stability, Energy Technol. 7 (2019), https://doi.org/ 10.1002/ente.201801090. X. Hu, Y.H. Wang, B. Ding, X.L. Wu, A novel way to synthesize nitrogen doped porous carbon materials with high rate performance and energy density for supercapacitors, J. Alloy. Comp. 785 (2019) 110e116. D.W. Wang, F. Li, M. Liu, G.Q. Lu, H.M. Cheng, 3D aperiodic hierarchical porous graphitic carbon material for high-rate electrochemical capacitive energy storage, Angew. Chem. Int. Ed. 47 (2008) 373e376. L. Qie, W. Chen, H. Xu, X. Xiong, Y. Jiang, F. Zou, X. Hu, Y. Xin, Z. Zhang, Y. Huang, Synthesis of functionalized 3D hierarchical porous carbon for highperformance supercapacitors, Energy Environ. Sci. 6 (2013) 2497e2504. X.L. Wu, L.L. Jiang, C.L. Long, Z.J. Fan, From flour to honeycomb-like carbon foam: carbon makes room for high energy density supercapacitors, Nano Energy 13 (2015) 527e536. X. Hu, X.H. Xu, R.Q. Zhong, L.J. Shang, H.T. Ma, X.L. Wu, P.Y. Jia, Facile synthesis of microporous carbons wit three-dimensional honeycomb-like porous structure for high performance supercapacitors, J. Electroanal. Chem. 823 (2018) 54e60. D. Guo, B. Ding, X. Hu, Y.H. Wang, F.Q. Han, X.L. Wu, Synthesis of boron and nitrogen codoped porous carbon foam for high performance supercapacitors, ACS Sustain. Chem. Eng. 6 (2018) 11441e11449. S. Dutta, A. Bhaumik, K. Wu, Hierarchically porous carbon derived from polymers and biomass: effect of interconnected pores on energy applications, Energy Environ. Sci. 7 (2014) 3574e3592. X.N. Kang, H. Zhu, C.Y. Wang, K. Sun, J. Yin, Biomass derived hierarchically porous and heteroatom-doped carbons for supercapacitors, J. Colloid Interface Sci. 509 (2018) 369e383. L. Peng, Y.R. Liang, H.W. Dong, H. Hu, X. Zhao, Y.J. Cai, Y. Xiao, Y.L. Liu, M.T. Zheng, Super-hierarchical porous carbons derived from mixed biomass wastes by a stepwise removal strategy for high-performance supercapacitors, J. Power Sources 377 (2018) 151e160. B. Men, P.K. Guo, Y.Z. Sun1, Y. Tang, Y.M. Chen, J.Q. Pan, P.Y. Wan, High-performance nitrogen-doped hierarchical porous carbon derived from cauliflower for advanced supercapacitors, J. Mater. Sci. 54 (2019) 2446e2457. K.X. Zou, Y.F. Denga, J.P. Chen, Y.Q. Qian, Y.W. Yang, Y.W. Li, G.H. Chen, Hierarchically porous nitrogen-doped carbon derived from the activation of agriculture waste by potassium hydroxide and urea for high-performance supercapacitors, J. Power Sources 378 (2018) 579e588. M.J. Kwak, A. Ramadoss, K.Y. Yoon, J. Park, P. Thiyagarajan, J.H. Jang, Singlestep synthesis of N-doped three-dimensional graphitic foams for highperformance supercapacitors, ACS Sustain. Chem. Eng. 5 (2017) 6950e6957. Q. Wang, J. Yan, Y. Wang, G. Ning, Z.J. Fan, T. Wei, J. Cheng, M. Zhang, X. Jing, Template synthesis of hollow carbon spheres anchored on carbon nanotubes for high rate performance supercapacitors, Carbon 52 (2013) 209e218. X.L. Han, H.X. Jiang, Y. Zhou, W.F. Hong, Y.F. Zhou, P. Gao, R. Ding, E.H. Liu, A high performance nitrogen-doped porous activated carbon for supercapacitor derived from pueraria, J. Alloy. Comp. 744 (2018) 544e551. S.S. Qu, J.F. Wan, C.C. Dai, T.Y. Jin, F.W. Ma, Promising as high-performance supercapacitor electrode materials porous carbons derived from biological lotus leaf, J. Alloy. Comp. 751 (2018) 107e116.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Facile synthesis of three-dimensional interconnected porous carbon derived from potassium alginate for high performance supercapacitor Shuxian Sun, Bing Ding, Ruonan Liu, Xiaoliang Wu* Department of Chemistry and Chemical Engineering, College of Science, Northeast Forestry University, 26 Hexing Road, Harbin, 150040, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 April 2019 Received in revised form 16 June 2019 Accepted 17 June 2019 Available online 18 June 2019
Porous carbon obtained by the conventional two-step way (chemical activation after carbonization) is confronted with the problems of long time-consuming, high cost and undeveloped macropore structure. Herein, for the first time, we report a facile and scalable way for the construction of three-dimensional (3D) interconnected porous carbons (IPC) originated from potassium alginate by a self-activation process. Owing to the high surface area, 3D interconnected ion diffusion channel and massive oxygen functional groups, the optimized IPC-800 electrode displays a high specific capacity of 279 F g1 at 1 A g1, superior rate capability (200 F g1 at 50 A g1) and excellent electrochemical stability with 96.6% capacitance retention after 10000 cycles in 6 M KOH aqueous electrolyte. Moreover, the assembled IPC-800//IPC-800 symmetric supercapacitor shows an energy density of 16.9 Wh kg1 and good electrochemical stability in 1 M Na2SO4 aqueous electrolyte. These exciting results indicate a facile, economical and scalable method for the synthesis of porous carbon materials for high performance supercapacitors. © 2019 Elsevier B.V. All rights reserved.
Keywords: Self-activation Potassium alginate Supercapacitors Energy density
1. Introduction Recently, with the increasing demand for energy and environmental pollution increasingly serious, there is no denying that the demand for renewable energy storage devices has become evermore urgent [1,2]. As a new energy storage device, supercapacitors have received massive attentions owing to the high power density, good cycling stability, rapid charge/discharge rate and low maintenance cost [3e6]. Generally, according to energy storage mechanism, supercapacitors can be classified into two types: electrical double-layer capacitors (EDLCs) and pseudocapacitors. Due to the rapid reversible adsorption and desorption of electrolyte ions in the double layer, EDLCs have higher power density and better cycling stability than pseudocapacitors. Porous carbon materials have been widely used in EDLCs owing to their appealing properties, for example, high specific surface area, numerous raw materials, and excellent electrochemical stability [7e10]. The traditional method for the construction of porous carbon mainly via two steps: carbon precursors are firstly carbonized in inert gas and then followed by activation with activating agent (KOH, ZnCl2, etc). However, the production process is
* Corresponding author. E-mail address: [email protected] (X. Wu). https://doi.org/10.1016/j.jallcom.2019.06.212 0925-8388/© 2019 Elsevier B.V. All rights reserved.
complicated, time-consuming and these activating agents severely corrode equipment, which are serious obstacles to large-scale production [11,12]. Moreover, porous carbon prepared by conventional way is confronted with high ion-transport resistance and insufficient ion diffusion, which result in low specific capacity and poor rate characteristic [13]. Recently, three-dimensional (3D) interconnected porous carbon with large specific surface area, hierarchical pore structure is desirable for high-performance electrode materials of supercapacitors [14e17]. The 3D interconnected hierarchical porous framework can not only provide large specific surface area to store charges, but also shorten ion diffusion distance, which has drawn numerous concerns [14]. However, the construction of 3D interconnected hierarchical porous carbon usually needs the tempting method including massive time-consuming procedure with template preparation, template removal, and post-activation, which are serious obstacles to large-scale production [18e20]. Herein, for the first time, we report a facile and scalable way for the construction of 3D interconnected porous carbons (IPC) originated from potassium alginate by a self-activation process. Owing to the large surface area, 3D interconnected ion diffusion channel and massive oxygen functional groups, the optimized IPC-800 electrode displays a high specific capacity of 279 F g1 at 1 A g1, superior rate capability and excellent electrochemical stability with 96.6% capacitance retention after 10000 cycles. Moreover, the
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S. Sun et al. / Journal of Alloys and Compounds 803 (2019) 401e406
assembled IPC-800//IPC-800 symmetric supercapacitor shows an energy density of 16.9 Wh kg1 and excellent electrochemical stability.
2. Material and methods 2.1. Construction of materials 3 g potassium alginate was directly carbonized at various temperatures (700, 800, 900 C) for 2 h in N2 atmosphere. The products were bathed by dilute HCl solution and gently stirred for 12 h. After that, the obtained samples were filtered and washed with distill water and ethanol. At last, the samples were dried in a vacuum dryer. The obtained materials were denoted as IPC-x, which x represents the temperature of carbonization temperature. The prepared process was shown in Scheme 1.
2.2. Characterizations The microstructures of the obtained samples were conducted by scanning electron microscopy (SEM, JEOL JSM-7500F) and transmission electron microscopy (TEM, JEOL JEM2010). The crystal structure was characterized by X-ray diffraction (XRD). The X-ray photoelectron spectroscopy (XPS) measurement was studied with Thermo ESCALAB 250XI spectrometer. Nitrogen adsorption/ desorption curves were checked by Autosorb IQ. The pore characteristics of nitrogen adsorption/desorption were measured by BET method, and the pore size distribution was calculated by density functional theory (DFT). 2.3. Electrochemical measurements In a three-electrode system, the working electrodes are prepared as follows: acetylene black (20 wt%), active materials (75 wt %) and polytetrafluoroethylene (5 wt%) form paste in ethanol. Then
Scheme 1. Schematic diagram illustrating the construction of the IPC materials using potassium alginate as the precursor.
Fig. 1. (a, b) SEM images of IPC-800. (c) TEM image of IPC-800. (d) High resolution TEM image of IPC-800.
S. Sun et al. / Journal of Alloys and Compounds 803 (2019) 401e406
evenly spread on foam nickel and vacuum dry at 60 C overnight, the loading mass is about 3 mg cm2. By using platinum foil as counter electrode, active material coated with Ni foam as working electrode and the Hg/HgO electrode is selected as reference electrode for measurement in 6 M KOH aqueous electrolyte. The electrochemical performance of the synthesized carbon materials was also evaluated in symmetrical device using two-electrode system in 1 M Na2SO4 solution. All measurements were tested by electrochemical workstation (CHI 660E). The specific capacitance (C) of the three-electrode system is calculated by equation (1), and the specific capacitance, power density (P) and energy density (E) of the symmetrical device are calculated by the following equations: C ¼ (I Dt)/(m DV)
(1)
C ¼ (!I dV)/(n mV)
(2)
E ¼ 0.5CV2
(3)
P ¼ E/Dt
(4)
In formula (1), I denotes current density, m denotes the mass of active material in a single electrode, Dt denotes the discharge time, DV denotes potential window. In formula (2), (3) and (4), I stands current density, n represents the scan rate, m symbolizes the weight of the active materials of the two electrodes and Dt is the time of discharge, V is the voltage window.
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3. Results and discussions The micromorphologies of the obtained materials were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As seen in Fig. 1a and b, the IPC-800 samples display 3D interconnected porous framework with massive macropores. TEM image further confirms its unique 3D highly interconnected porous framework, which can not only provide available large specific surface area to store charges, but also shorten ion diffusion distance. Moreover, the high resolution TEM image of the IPC-800 samples show a great deal of micropores in the surface of carbon framework, which is in favor of charge storage. The IPC samples obtained at other temperatures also display 3D interconnected porous structure (Figs. S1a and b). With the increase of carbonization temperature, partly carbon wall gradually fragments and pore size enlarge due to the high temperature is conducive to activation. The decomposition process of potassium alginate was checked through thermogravimetric analysis (TGA). As seen in Fig. 2a, the TGA curve exhibits two weight loss steps in the temperature regions of 200e500 C and 700e800 C, which are corresponding to the decomposition of organic moiety with simultaneously to the formation of potassium carbonate and further reaction of potassium oxide with carbon (K2O þ C / 2K þ CO) produced by decomposition of potassium carbonate (K2CO3 / K2O þ CO2), respectively. X-ray diffraction (XRD) analysis was adopted to research the crystalline characteristic of the IPC samples (Fig. 2b). All IPC
Fig. 2. (a) TGA curve of potassium alginate. (b) XRD curves of IPC-700, IPC-800 and IPC-900. (c) XPS survey spectrum of IPC-800. (d) C 1s high-resolution spectra of IPC-800.
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Fig. 3. (a) N2 adsorption/desorption isotherms of IPC-700, IPC-800, IPC-900. (b) Pore sizes distribution of IPC-700, IPC-800, IPC-900.
materials show two broad characteristic peaks at 22.5 and 43.6 , which are attributed to the (002) and (101) crystal planes of the carbon material, respectively. The weak and broaden diffraction peaks indicate that the IPC-800 materials have massive defects and disordered structure. The surface characteristics of the IPC-800 materials were conducted by X-ray photoelectron spectra (XPS). As seen in Fig. 2c, the O content of IPC-800 can reach 9.0 at%. As seen in Fig. 2d, the C1s peak can be divided into four individual peaks: CeC (284.8 eV), CeOH (285.2 eV), C]O (287.1 eV) and COOH (289.23 eV), respectively [19,21]. The porous characteristics of the obtained samples were further investigated by N2 adsorption/desorption isothermals. As seen in Fig. 3a, the IPC-800 samples show a combined characteristic of I/IV type adsorptionedesorption isothermal. Moreover, the adsorption capacity increased sharply at the relative pressure P/P0 from 0 to 0.3 can be found, indicating that the IPC-800 samples possess massive micropores. The detailed pore structure information is listed in Table 1. The IPC-800 samples show a high specific surface area of 1145.8 m2 g1 with a high pore volume up to 0.58 cm3 g1 calculated by the BrunauereEmmetteTeller (BET) way. The pore size distribution of the IPC-800 samples show massive micropores and suitable mespores (Fig. 3b). Owing to the large surface area, 3D interconnected ion diffusion channel and massive oxygen functional groups, the IPC-800 samples are expected to be an outstanding candidate for supercapacitors. The electrochemical properties of the as-obtained samples were firstly evaluated by cyclic voltammetry (CV) using a three-electrode system in 6 M KOH aqueous electrolyte. Fig. 4a presents the profiles of the obtained materials at various carbonization temperatures. All the samples show quasi-rectangular profile without any redox peaks, indicating a perfect capacitive characteristic. Evidently, the IPC-800 electrode presents the largest
area surrounded by CV curves corresponding to the highest specific capacitance. Moreover, even at a high scan rate of 500 mV s1 (Fig. 4b), the CV profile of the IPC-800 electrode still maintains superior quasi-rectangular in shape, indicating excellent rate performance. Fig. 4c presents the galvanostatic charge/discharge profiles of the IPC-800 electrode at various current densities. All curves exhibit isosceles triangular shapes, demonstrating an ideal capacitive characteristic. The specific capacitance of the IPC-800 electrode evaluated by the discharge curves is 279 F g1 at 1 A g1 (Fig. 4d), which is much higher than commercial activated carbon (YP-50), IPC-700 and IPC-900. Notably, the IPC-800 electrode shows a high capacity retention rate of 71.7% (200 F g1) at 50 A g1, demonstrating fast charge and discharge rate at high current density. As displayed in Fig. 4e, the IPC-800 electrode displays the superior cycling stability with capacitance retention of about 96.6% after 10000 cycles, demonstrating excellent electrochemical stabilization. Nyquist plots of the IPC-800 electrode are displayed in Fig. 4f. In the high frequency areas, the IPC-800 electrode displays a low equivalent series resistance of 0.55 U, confirming good conductivity. In the low frequency, the IPC-800 electrode displays a nearly vertical line, demonstrating fast electron transport. After 10000 cycles of CV tests, Nyquist plots of the IPC-800 electrode almost no change in shape, further indicating excellent electrochemical stability. To further demonstrate the excellent electrochemical capability of IPC-800, a symmetric supercapacitor according to the IPC-800 electrodes using a two-electrode system was assembled. As reported by literature, alkali metal sulfate aqueous solutions can achieve a wider voltage region than alkaline solutions, which is propitious to achieve high energy density [22]. Therefore, the IPC800//IPC-800 symmetric supercapacitor was conducted in 1 M Na2SO4 aqueous electrolyte. Fig. 5a displays the IPC-800//IPC-800
Table 1 Physical parameters of the as-prepared carbon materials. Samples
SBET (m2 g1)a
Smic(m2 g1)b
Sext(m2 g1)c
Vtotal (cm3 g1)d
D (nm)e
IPC-700 IPC-800 IPC-900
722.0 1145.8 1281.8
623.5 957.7 1006.4
98.5 188.1 275.4
0.3541 0.5759 0.7150
1.96 2.01 2.23
a b c d e
Specific surface area (SBET) was calculated with modified Brunauer-Emmett-Teller (BET) method. Micropore specific surface area (Vmic) was obtained from t-plot method. External pore volume (Sext) was obtained from t-plot method (Sext ¼ SBET - Smic). Total pore volume (Vtotal) was estimated from the adsorbed amount at a relative pressure of 0.99. Average pore diameter (D) was obtained from D ¼ 4Vtotal/SBET.
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Fig. 4. (a) CV curves of IPC-700, IPC-800 and IPC-900 at 50 mV s1. (b) CV curves of IPC-800 at different scan rates. (c) GCD curves of IPC-800 at different current densities. (d) Specific capacitance of YP-50, IPC-700, IPC-800 and IPC-900 at different current densities. (e) Electrochemical stability of IPC-800 at 100 mV s1 for 10000 cycles. (f) Nyquist plots of the IPC-800 electrode before and after 10000 cycles.
Fig. 5. (a) CV curves of the IPC-800//IPC-800 symmetrical supercapacitor in different operation voltages at 50 mv s1. (b) CV curves of the IPC-800//IPC-800 symmetrical supercapacitor at different scan rate from 50 to 200 mV s1. (c) Ragone plots of the IPC-800//IPC-800 symmetrical supercapacitor and previously reported carbon-based symmetrical supercapacitors. (d) Electrochemical stability of the IPC-800//IPC-800 symmetrical supercapacitor tested at 100 mV s1 for 10000 cycles.
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symmetric supercapacitor at different voltage ranges. Clearly, it can be seen that the stable voltage range for the IPC-800//IPC-800 symmetric supercapacitor was 0e1.6 V. Fig. 5b displays the CV profiles of the symmetric supercapacitor at various scan rates from 50 to 200 mV s1. All the profiles show rectangular-like shapes and even at 200 mV s1 without the obvious deformation, suggesting outstanding rate characteristics. Owing to the wide voltage region and large specific capacity, the IPC-800//IPC-800 symmetric supercapacitor shows an energy density of 16.9 Wh kg1 (Fig. 5c), higher than previously reported porous carbon symmetric supercapacitors in aqueous electrolyte [23e26]. As displayed in Fig. 5d, the IPC-800//IPC-800 symmetric supercapacitor displays a good cycling stability with capacity retention of about 97.0% after 10000 cycles, indicating good electrochemical stability. 4. Conclusion In summary, we report a facile and scalable way for the construction of 3D interconnected porous carbons originated from potassium alginate by a self-activation process. Owing to the large surface area, 3D interconnected ion diffusion channel and massive oxygen functional groups, the optimized IPC-800 electrode displays high specific capacity, superior rate feature and excellent cycling stability. Moreover, the assembled IPC-800//IPC-800 symmetric supercapacitor shows high energy density and excellent electrochemical stability. Conflicts of interest Authors declare no conflict of interests.
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Acknowledgement [19]
All authors are very grateful for the financial support of the National Natural Science Foundation of China (51702043), Heilongjiang Postdoctoral Foundation (LBH-Z18008).
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Appendix A. Supplementary data
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Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.06.212.
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References [1] C. Liu, F. Li, L. Ma, H. Cheng, Advanced materials for energy storage, Adv. Mater. 22 (2010) 28e62. [2] P. Simon, Y. Gogotsi, Capacitive energy storage in nanostructured carbon electrolyte systems, Acc. Chem. Res. 46 (2013) 1094e1103. [3] T.Y. Liu, F. Zhang, Y. Song, Y. Li, Revitalizing carbon supercapacitor electrodes with hierarchical porous structures, J. Mater. Chem. A 5 (2017) 17705e17733. [4] J.Y. Hwang, M. Li, M.F. El-Kady, R.B. Kaner, Next-generation activated carbon supercapacitors: a simple step in electrode processing leads to remarkable gains in energy density, Adv. Funct. Mater. 27 (2017) 1605745. [5] H. Jiang, P.S. Lee, C. Li, 3D carbon based nanostructures for advanced supercapacitors, Energy Environ. Sci. 6 (2013) 41e53. [6] X.L. Wu, L.L. Jiang, C.L. Long, T. Wei, Z.J. Fan, Dual support system ensuring
[23]
[24]
[25]
[26]
porous CoeAl hydroxide nanosheets with ultrahigh rate performance and high energy density for supercapacitors, Adv. Funct. Mater. 25 (2015) 1648e1655. B. Ding, D. Guo, Y.H. Wang, X.L. Wu, Z.J. Fan, Functionalized graphene nanosheets decorated on carbon nanotubes networks for high performance supercapacitors, J. Power Sources 398 (2018) 113e119. J.H. Cao, C.Y. Zhu, Y. Aoki, H. Habazaki, Starch-derived hierarchical porous carbon with controlled porosity for high performance supercapacitors, ACS Sustain. Chem. Eng. 6 (2018) 7292e7303. C. Liang, J. Bao, C. Li, H. Huang, C. Chen, Y. Lou, H. Lu, H. Lin, Z. Shi, S. Feng, Onedimensional hierarchically porous carbon from biomass with high capacitance as supercapacitor materials, Micropor. Mesopor. Mat. 251 (2017) 77e82. J.L. Zhang, W.F. Zhang, H. Zhang, J. Pang, G.P. Cao, M.F. Han, Y.S. Yang, A novel synthesis of hierarchical porous carbons from resol by potassium acetate activation for high performance supercapacitor electrodes, J. Alloy. Comp. 712 (2017) 76e81. S.H. Kang, B.N. Kim, I.G. Kim, Facile synthesis of porous carbon via self-activation of potassium acetate for high performance supercapacitor electrodes with excellent cyclic stability, Energy Technol. 7 (2019), https://doi.org/ 10.1002/ente.201801090. X. Hu, Y.H. Wang, B. Ding, X.L. Wu, A novel way to synthesize nitrogen doped porous carbon materials with high rate performance and energy density for supercapacitors, J. Alloy. Comp. 785 (2019) 110e116. D.W. Wang, F. Li, M. Liu, G.Q. Lu, H.M. Cheng, 3D aperiodic hierarchical porous graphitic carbon material for high-rate electrochemical capacitive energy storage, Angew. Chem. Int. Ed. 47 (2008) 373e376. L. Qie, W. Chen, H. Xu, X. Xiong, Y. Jiang, F. Zou, X. Hu, Y. Xin, Z. Zhang, Y. Huang, Synthesis of functionalized 3D hierarchical porous carbon for highperformance supercapacitors, Energy Environ. Sci. 6 (2013) 2497e2504. X.L. Wu, L.L. Jiang, C.L. Long, Z.J. Fan, From flour to honeycomb-like carbon foam: carbon makes room for high energy density supercapacitors, Nano Energy 13 (2015) 527e536. X. Hu, X.H. Xu, R.Q. Zhong, L.J. Shang, H.T. Ma, X.L. Wu, P.Y. Jia, Facile synthesis of microporous carbons wit three-dimensional honeycomb-like porous structure for high performance supercapacitors, J. Electroanal. Chem. 823 (2018) 54e60. D. Guo, B. Ding, X. Hu, Y.H. Wang, F.Q. Han, X.L. Wu, Synthesis of boron and nitrogen codoped porous carbon foam for high performance supercapacitors, ACS Sustain. Chem. Eng. 6 (2018) 11441e11449. S. Dutta, A. Bhaumik, K. Wu, Hierarchically porous carbon derived from polymers and biomass: effect of interconnected pores on energy applications, Energy Environ. Sci. 7 (2014) 3574e3592. X.N. Kang, H. Zhu, C.Y. Wang, K. Sun, J. Yin, Biomass derived hierarchically porous and heteroatom-doped carbons for supercapacitors, J. Colloid Interface Sci. 509 (2018) 369e383. L. Peng, Y.R. Liang, H.W. Dong, H. Hu, X. Zhao, Y.J. Cai, Y. Xiao, Y.L. Liu, M.T. Zheng, Super-hierarchical porous carbons derived from mixed biomass wastes by a stepwise removal strategy for high-performance supercapacitors, J. Power Sources 377 (2018) 151e160. B. Men, P.K. Guo, Y.Z. Sun1, Y. Tang, Y.M. Chen, J.Q. Pan, P.Y. Wan, High-performance nitrogen-doped hierarchical porous carbon derived from cauliflower for advanced supercapacitors, J. Mater. Sci. 54 (2019) 2446e2457. K.X. Zou, Y.F. Denga, J.P. Chen, Y.Q. Qian, Y.W. Yang, Y.W. Li, G.H. Chen, Hierarchically porous nitrogen-doped carbon derived from the activation of agriculture waste by potassium hydroxide and urea for high-performance supercapacitors, J. Power Sources 378 (2018) 579e588. M.J. Kwak, A. Ramadoss, K.Y. Yoon, J. Park, P. Thiyagarajan, J.H. Jang, Singlestep synthesis of N-doped three-dimensional graphitic foams for highperformance supercapacitors, ACS Sustain. Chem. Eng. 5 (2017) 6950e6957. Q. Wang, J. Yan, Y. Wang, G. Ning, Z.J. Fan, T. Wei, J. Cheng, M. Zhang, X. Jing, Template synthesis of hollow carbon spheres anchored on carbon nanotubes for high rate performance supercapacitors, Carbon 52 (2013) 209e218. X.L. Han, H.X. Jiang, Y. Zhou, W.F. Hong, Y.F. Zhou, P. Gao, R. Ding, E.H. Liu, A high performance nitrogen-doped porous activated carbon for supercapacitor derived from pueraria, J. Alloy. Comp. 744 (2018) 544e551. S.S. Qu, J.F. Wan, C.C. Dai, T.Y. Jin, F.W. Ma, Promising as high-performance supercapacitor electrode materials porous carbons derived from biological lotus leaf, J. Alloy. Comp. 751 (2018) 107e116.