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A novel hydrochar and nickel composite for the electrochemical supercapacitor electrode material
Materials Letters 74 (2012) 111–114
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A novel hydrochar and nickel composite for the electrochemical supercapacitor electrode material Lili Ding, Zichen Wang, Yannan Li, Yalei Du, Hequn Liu, Yupeng Guo ⁎ Department of Chemistry, Jilin University, Qianjin Street 2699, Changchun 130012, China
a r t i c l e
i n f o
Article history: Received 16 December 2011 Accepted 17 January 2012 Available online 24 January 2012 Keywords: Hydrochar Nickel Supercapacitor Rice husk Carbon materials Composite materials
a b s t r a c t The novel electrochemical supercapacitor anode material hydrochar/nickel composite was prepared from biomass via a facile method in this paper. Hydrochar was synthesized by sulfuric acid hydrolysis solution of rice husk. The nickel, acted as graphitization catalyst, effectively changed the graphitization degree of hydrochar. Then the hydrochar/nickel effectively improved the specific capacity of hydrochar by 149%. Hydrochar/nickel presented a specific capacitance of 174.5 F g− 1, which was higher than the activated carbon/nickel. The electrochemical performance of the hydrochar, activated carbon and their composites was investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. The better capacitive behavior of the hydrochar/ nickel composite illuminated a promising electrode material for electrochemical supercapacitor. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Supercapacitor is the most promising electrochemical energy storage device due to its high power capability, large energy density and long cycle life [1–3]. Carbon materials, transition metal oxides and electronically conducting polymers are under close scrutiny for used as supercapacitor electrode materials [4–15]. The predominant capacitance of carbon materials and transition metal oxides electrodes arises from electrical double layers capacitance and pseudocapacitance separately [2,7]. Functional carbonaceous materials can be obtained by hydrothermal carbonization of carbohydrate and biomass. Hydrothermal carbon contains amounts of surface functional groups. The surface functional groups affect faradic reactions and wettability between the electrolyte solution and the carbon surface [8]. Decorating the carbon with metal or metal oxide nanoparticles could endow the hydrothermal carbon with specific properties and applications, such as catalyst supports, adsorbents, electrodes and so on. The specific capacitance of activated carbon/nickel oxide increased by 10.84% compared with activated carbon [9]. The specific capacitance of nickel oxide/carbon nanotube had been increased by 34% as against carbon nanotube [10]. Lots of studies for the enhancement of capacitance focused on metal oxides and carbon composites, however, the researches on pure nickel and carbon complexes are few. In a previous work, we have successfully prepared hydrochar from the rice husk [11], the hydrochar has already been applied in the
⁎ Corresponding author. Tel./fax: + 86 431 8515 5358. E-mail address: [email protected] (Y. Guo). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.01.070
preparation of porous carbon and carbon black [12,13]. Here, we further expand the applications of hydrochar and developed the hydrochar/ nickel and activated carbon/nickel composites for the anode materials of electrochemical supercapacitor. The capacitance of hydrochar/nickel has a significant improvement compared with the hydrochar. 2. Experimental The preparation processes of the hydrochar/Ni composite included hydrothermal reaction, chemical precipitation and thermal annealing. Fig. 1 showed the schematic diagram of the preparation processes of hydrochar/nickel. The preparation methods of the hydrochar and activated carbon were as our previous studies [11,12]. The nickelous acetate was a source of nickel and the 2 mol L − 1 sodium hydroxide was precipitant. The hydrochar/nickel and activated carbon/nickel composites were obtained after annealing at 800 °C for 1 h. The transmission electron microscope (TEM) images of the samples were observed using a Hitachi H-800 transmission electron microscope. The structure and lattice constant were analyzed by powder X-ray diffraction (XRD, MADZU, Japan). Electrochemical performance measurements were conducted on the CHI 6600 electrochemical workstation in 6 mol L − 1 KOH aqueous solution. The working electrodes were fabricated by mixing 80 wt.% as-prepared samples, 10 wt.% acetylene black and 10 wt.% polytetrafluoroethylene. Saturated calomel electrode and platinum foil were used as the reference electrode and the counter electrode, respectively. Cyclic voltammetry (CV) was carried out at the scan rate of 10 mV s − 1 and the galvanostatic charge/discharge measurement was performed at a current load of 50 mA cm− 2.
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L. Ding et al. / Materials Letters 74 (2012) 111–114
Fig. 1. Schematic illustration of the preparation processes of hydrochar/Ni.
3. Results and discussion 3.1. TEM The morphology, size and the status of agglomeration of the samples were analyzed by TEM (Fig. 2). The Ni particles are spherical and display a size distribution in the range of 50–90 nm. Meanwhile, the particles are weak agglomeration. It might be a result of heterogeneous precipitation. The Ni particles dispersed on the surface of the hydrochar were more uniform than that dispersed on the activated carbon. There were scarcely any pores on the hydrochar. 3.2. XRD The crystal structures of the samples were analyzed by XRD. Fig. 3A(b) and 3A(d) presents the XRD patterns of hydrochar/Ni and activated carbon/Ni composites. Three sharp diffraction peaks of hydrochar/Ni at 2θ = 44.51°, 51.85° and 76.37° (corresponding to (111), (200), and (220) reflections, respectively) can be attributable to Ni. Two sharp diffraction peaks of activated carbon/Ni at 2θ = 44.51° and 76.37° match well with the (111) and (220) planes of Nickel structure though Fig. 3A(d) does not show (200) peak of Ni. Nickel oxide was reduced to metallic nickel in the high temprature,which was verified
by the previous report, the carbonthermal reduction can take place in the high temprature and the metal oxide could be completely reduced to metal [14]. It confirmed that nickel was loaded on the hydrochar and activated carbon. However, different surface properties of the hydrochar and activated carbon made the processes of carbonthermal reduction different, which made the final products show different diffraction peaks. The characteristic peaks of carbon at 2θ = 43.93°, 64.35°, 77.43° are sharp. The peak at 2θ = 37.77° was a hydrogen acetate peak. The hydrochar and activated carbon presented broad amorphous carbon diffraction peaks in a range of 10°–30°. However, the hydrochar/nickel showed a sharp graphite peak at 2θ = 26°, which corresponded to the (002) reflection. The graphitization degree of hydrochar increased in the presence of nickel. This has been corroborated by recent report on the easy synthesis of graphitic carbon with nickel as the graphitization catalyst [15]. Therefore, the capacitive behavior of the peculiar hydrochar/Ni changed a lot. The activated carbon/Ni also contained nickel, but no sharp graphite peak appeared at 2θ = 26° instead of a broad peak similar to the hydrochar and activated carbon. This difference was relative to the presence of amounts of surface functional groups on the hydrochar [11], but in the activation reaction, these surface functional groups were involved in. Marta Sevilla described these catalytic graphitization processes, during the catalytic graphitization process, the metallic nanoparticles move through
Fig. 2. TEM micrographs of (a) hydrochar, (b) hydrochar/Ni, (c) activated carbon, and (d) activated carbon/Ni.
L. Ding et al. / Materials Letters 74 (2012) 111–114
Intensity(a.u.)
3200
A
2400 1600
b d c a
800 0 20
40
60
80
2θ(degree)
Current(A)
0.10
B
b d c a
0.05 0.00 -0.05 -0.10 -1.2
-0.8
-0.4
0.0
0.4
Potentive V vs SCE(V)
Potential(V)
0.4
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ac
d b
0.0
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these materials. There was no obvious redox peak of nickel oxide in the CV curves, which confirmed the results of XRD. Fig. 3C displayed the galvanostatic charge/discharge curves of the prepared materials tested at 50 mA cm− 2 in 6 mol L − 1 KOH. The four curves presented similar isosceles triangle shape. The capacitance trend was consistent with the results of Fig. 3B. According to the Fig. 3C, the exact specific capacitances of the hydrochar, hydrochar/Ni, activated carbon and activated carbon/Ni are 79.5 F g− 1, 174.5 F g− 1, 108.2 F g− 1 and 154.2 F g− 1, respectively. Fewest capacitive behaviors were observed from the CV and galvanostatic charge discharge curves of the pure hydrochar electrode. The activated carbon presented a higher capacitive than the hydrochar, because it could generate a lot of pores (BET = 1355 m 2 g− 1) in the hydrochar through the activation reaction. The porous carbon also provided both sufficient ion transport routes and elastic buffers for releasing the strain in the process of ion conduction [16]. Loading the nickel on the hydrochar and the activated carbon made the capacitance changed. Here, the prepared nickel particles were nanoparticles and the size effects could change the transport of mass and charge, their special phenomena had triggered great attention. The nanoparticles have showed efficient energy conversion and storage performance in the literature [17]. Therefore, the existence of the nickel nanoparticles can contribute to the transmission of electron in solution and help to the increase of capacitance. But for the activated carbon, part of the nickel particles plugged the pores and hindered the ion diffusion into the pores, thereby reducing the capacitance. Therefore the enhancement of capacitance of activated carbon/nickel was less than the hydrochar/nickel. Another explanation for this was the difference in graphitization degree of these samples. The graphitic structures of carbons, size effects, uniformity and content of nickel particles may be used to explain the capacity changes. Taking into account the impact of these factors, it is not surprising that the amount of the increase in capacitance of activated carbon/nickel was less than hydrochar/nickel.
-0.4
4. Conclusions -0.8 -1.2 0
50
100
150
200
Time(s) Fig. 3. (A) XRD patterns, (B) CV curves, and (C) Galvanostatic charging/discharging curves of the (a) hydrochar, (b) hydrochar/Ni, (c) activated carbon, and (d) activated carbon/Ni.
the amorphous carbon, leaving behind a track of graphitic carbon in accordance with a dissolution–precipitation mechanism [15]. In the following carbonthermal reduction reaction, the activated carbon did not have so many functional groups to interact with nickelous acetate, which was not conducive to the formation of nickel to some extent. This may be a reason for a large number of nickel (30.3 wt.%) presented on the surface of hydrochar, but only a small content of nickel (2.6 wt.%) loaded on the activated carbon under the same preparation conditions. The huge difference in nickel content between hydrochar and activated carbon indicated the formation of hydrochar/nickel more easily than activated carbon/nickel composite, which was consistent with Fig. 2b and d, uniform and more nickel dispersed on the hydrochar.
3.3. Electrochemical properties The electrochemical properties of these materials were investigated by CV and galvanostatic charge/discharge techniques. Fig. 3B showed the CV curves at the scan rates of 10 mV s− 1. The four curves presented similar rectangular shape, which indicated the capacitive behaviors of
In summary, the new electrode material hydrochar/nicke composite based on rice husk was prepared by a series of processes, including hydrothermal reaction, chemical precipitation and thermal annealing. This method, which was easy to load nickel on carbon, can be applied in fabrication of other metals and hydrochar composites. The specific capacity of the hydrochar had been effectively improved by 149% through the function of nickel. The hydrochar/nickel showed a specific capacitance of 174.5 F g − 1. This work laid the foundation for the further exploration of ways to improve the capacity of hydrochar. The applications of hydrochar and metal composites are not limited to the capacitor electrodes, they also can be applied to other energy storage devices (such as lithium ion battery), catalytic materials, magnetic materials and so on. Acknowledgments This research work was supported by the Key Project of the National Eleventh Five-Year Research Program of China (2008BAE66B00), Scientific and Technological Planning Project of Jilin Province (20075009 and 20100326) and Interdisciplinary Research Project of Jilin University (201003030). References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Yuan G, Jiang Z, Aramata A, Gao Y. Carbon 2005;43:2913. Zhang LL, Zhao XS. Chem Soc Rev 2009;38:2520. Simon P, Gogotsi Y. Nat Mater 2008;7:852. Subramanian V, Hall SC, Smith PH, Rambabu B. Solid State Ion 2004;175:511. Frackowiak E. Phys Chem Chem Phys 2007;9:1874. Wang K, Huang J, Wei Z. J Phys Chem C 2010;114:8062. Liu XM, Zhang XG, Fu SH. Mater Res Bull 2006;41:620. Deng JJ, Deng JC, Liu ZH, Deng HR, Liu B. J Mater Sci 2009;44:2828. Guo HY, Zhao HJ, Akiko A, Gao YZ. Carbon 2005;43:2913–7.
114 [10] [11] [12] [13]
L. Ding et al. / Materials Letters 74 (2012) 111–114 Lee JY, Liang K, An KH, Lee YH. Synth Mat 2005;150:153. Wang L, Guo Y, Zhu Y, Li Y, Qu Y, Rong C. Bioresour Technol 2010;101:9808. Wang L, Guo Y, Zou B, Li Y, Rong C, Ma X, et al. Bioresour Technol 2011;102:1947–50. Wang L, Wang X, Zou B, Ma X, Qu Y, Rong C, et al. Bioresour Technol 2011;102: 8220–4.
[14] [15] [16] [17]
Lou XW, Chen JS, Chen P, Archer LA. Chem Mater 2009;21:2872. Sevilla M, Fuertes AB. Mater Chem Phys 2009;113:208–14. Wu X, Jiang LY, Cao FF, Guo YG, Wan LJ. Adv Mater 2009;21:2710–4. Balaya P. Energy Environ Sci 2008;1:645–54.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A novel hydrochar and nickel composite for the electrochemical supercapacitor electrode material Lili Ding, Zichen Wang, Yannan Li, Yalei Du, Hequn Liu, Yupeng Guo ⁎ Department of Chemistry, Jilin University, Qianjin Street 2699, Changchun 130012, China
a r t i c l e
i n f o
Article history: Received 16 December 2011 Accepted 17 January 2012 Available online 24 January 2012 Keywords: Hydrochar Nickel Supercapacitor Rice husk Carbon materials Composite materials
a b s t r a c t The novel electrochemical supercapacitor anode material hydrochar/nickel composite was prepared from biomass via a facile method in this paper. Hydrochar was synthesized by sulfuric acid hydrolysis solution of rice husk. The nickel, acted as graphitization catalyst, effectively changed the graphitization degree of hydrochar. Then the hydrochar/nickel effectively improved the specific capacity of hydrochar by 149%. Hydrochar/nickel presented a specific capacitance of 174.5 F g− 1, which was higher than the activated carbon/nickel. The electrochemical performance of the hydrochar, activated carbon and their composites was investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. The better capacitive behavior of the hydrochar/ nickel composite illuminated a promising electrode material for electrochemical supercapacitor. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Supercapacitor is the most promising electrochemical energy storage device due to its high power capability, large energy density and long cycle life [1–3]. Carbon materials, transition metal oxides and electronically conducting polymers are under close scrutiny for used as supercapacitor electrode materials [4–15]. The predominant capacitance of carbon materials and transition metal oxides electrodes arises from electrical double layers capacitance and pseudocapacitance separately [2,7]. Functional carbonaceous materials can be obtained by hydrothermal carbonization of carbohydrate and biomass. Hydrothermal carbon contains amounts of surface functional groups. The surface functional groups affect faradic reactions and wettability between the electrolyte solution and the carbon surface [8]. Decorating the carbon with metal or metal oxide nanoparticles could endow the hydrothermal carbon with specific properties and applications, such as catalyst supports, adsorbents, electrodes and so on. The specific capacitance of activated carbon/nickel oxide increased by 10.84% compared with activated carbon [9]. The specific capacitance of nickel oxide/carbon nanotube had been increased by 34% as against carbon nanotube [10]. Lots of studies for the enhancement of capacitance focused on metal oxides and carbon composites, however, the researches on pure nickel and carbon complexes are few. In a previous work, we have successfully prepared hydrochar from the rice husk [11], the hydrochar has already been applied in the
⁎ Corresponding author. Tel./fax: + 86 431 8515 5358. E-mail address: [email protected] (Y. Guo). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.01.070
preparation of porous carbon and carbon black [12,13]. Here, we further expand the applications of hydrochar and developed the hydrochar/ nickel and activated carbon/nickel composites for the anode materials of electrochemical supercapacitor. The capacitance of hydrochar/nickel has a significant improvement compared with the hydrochar. 2. Experimental The preparation processes of the hydrochar/Ni composite included hydrothermal reaction, chemical precipitation and thermal annealing. Fig. 1 showed the schematic diagram of the preparation processes of hydrochar/nickel. The preparation methods of the hydrochar and activated carbon were as our previous studies [11,12]. The nickelous acetate was a source of nickel and the 2 mol L − 1 sodium hydroxide was precipitant. The hydrochar/nickel and activated carbon/nickel composites were obtained after annealing at 800 °C for 1 h. The transmission electron microscope (TEM) images of the samples were observed using a Hitachi H-800 transmission electron microscope. The structure and lattice constant were analyzed by powder X-ray diffraction (XRD, MADZU, Japan). Electrochemical performance measurements were conducted on the CHI 6600 electrochemical workstation in 6 mol L − 1 KOH aqueous solution. The working electrodes were fabricated by mixing 80 wt.% as-prepared samples, 10 wt.% acetylene black and 10 wt.% polytetrafluoroethylene. Saturated calomel electrode and platinum foil were used as the reference electrode and the counter electrode, respectively. Cyclic voltammetry (CV) was carried out at the scan rate of 10 mV s − 1 and the galvanostatic charge/discharge measurement was performed at a current load of 50 mA cm− 2.
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L. Ding et al. / Materials Letters 74 (2012) 111–114
Fig. 1. Schematic illustration of the preparation processes of hydrochar/Ni.
3. Results and discussion 3.1. TEM The morphology, size and the status of agglomeration of the samples were analyzed by TEM (Fig. 2). The Ni particles are spherical and display a size distribution in the range of 50–90 nm. Meanwhile, the particles are weak agglomeration. It might be a result of heterogeneous precipitation. The Ni particles dispersed on the surface of the hydrochar were more uniform than that dispersed on the activated carbon. There were scarcely any pores on the hydrochar. 3.2. XRD The crystal structures of the samples were analyzed by XRD. Fig. 3A(b) and 3A(d) presents the XRD patterns of hydrochar/Ni and activated carbon/Ni composites. Three sharp diffraction peaks of hydrochar/Ni at 2θ = 44.51°, 51.85° and 76.37° (corresponding to (111), (200), and (220) reflections, respectively) can be attributable to Ni. Two sharp diffraction peaks of activated carbon/Ni at 2θ = 44.51° and 76.37° match well with the (111) and (220) planes of Nickel structure though Fig. 3A(d) does not show (200) peak of Ni. Nickel oxide was reduced to metallic nickel in the high temprature,which was verified
by the previous report, the carbonthermal reduction can take place in the high temprature and the metal oxide could be completely reduced to metal [14]. It confirmed that nickel was loaded on the hydrochar and activated carbon. However, different surface properties of the hydrochar and activated carbon made the processes of carbonthermal reduction different, which made the final products show different diffraction peaks. The characteristic peaks of carbon at 2θ = 43.93°, 64.35°, 77.43° are sharp. The peak at 2θ = 37.77° was a hydrogen acetate peak. The hydrochar and activated carbon presented broad amorphous carbon diffraction peaks in a range of 10°–30°. However, the hydrochar/nickel showed a sharp graphite peak at 2θ = 26°, which corresponded to the (002) reflection. The graphitization degree of hydrochar increased in the presence of nickel. This has been corroborated by recent report on the easy synthesis of graphitic carbon with nickel as the graphitization catalyst [15]. Therefore, the capacitive behavior of the peculiar hydrochar/Ni changed a lot. The activated carbon/Ni also contained nickel, but no sharp graphite peak appeared at 2θ = 26° instead of a broad peak similar to the hydrochar and activated carbon. This difference was relative to the presence of amounts of surface functional groups on the hydrochar [11], but in the activation reaction, these surface functional groups were involved in. Marta Sevilla described these catalytic graphitization processes, during the catalytic graphitization process, the metallic nanoparticles move through
Fig. 2. TEM micrographs of (a) hydrochar, (b) hydrochar/Ni, (c) activated carbon, and (d) activated carbon/Ni.
L. Ding et al. / Materials Letters 74 (2012) 111–114
Intensity(a.u.)
3200
A
2400 1600
b d c a
800 0 20
40
60
80
2θ(degree)
Current(A)
0.10
B
b d c a
0.05 0.00 -0.05 -0.10 -1.2
-0.8
-0.4
0.0
0.4
Potentive V vs SCE(V)
Potential(V)
0.4
C
ac
d b
0.0
113
these materials. There was no obvious redox peak of nickel oxide in the CV curves, which confirmed the results of XRD. Fig. 3C displayed the galvanostatic charge/discharge curves of the prepared materials tested at 50 mA cm− 2 in 6 mol L − 1 KOH. The four curves presented similar isosceles triangle shape. The capacitance trend was consistent with the results of Fig. 3B. According to the Fig. 3C, the exact specific capacitances of the hydrochar, hydrochar/Ni, activated carbon and activated carbon/Ni are 79.5 F g− 1, 174.5 F g− 1, 108.2 F g− 1 and 154.2 F g− 1, respectively. Fewest capacitive behaviors were observed from the CV and galvanostatic charge discharge curves of the pure hydrochar electrode. The activated carbon presented a higher capacitive than the hydrochar, because it could generate a lot of pores (BET = 1355 m 2 g− 1) in the hydrochar through the activation reaction. The porous carbon also provided both sufficient ion transport routes and elastic buffers for releasing the strain in the process of ion conduction [16]. Loading the nickel on the hydrochar and the activated carbon made the capacitance changed. Here, the prepared nickel particles were nanoparticles and the size effects could change the transport of mass and charge, their special phenomena had triggered great attention. The nanoparticles have showed efficient energy conversion and storage performance in the literature [17]. Therefore, the existence of the nickel nanoparticles can contribute to the transmission of electron in solution and help to the increase of capacitance. But for the activated carbon, part of the nickel particles plugged the pores and hindered the ion diffusion into the pores, thereby reducing the capacitance. Therefore the enhancement of capacitance of activated carbon/nickel was less than the hydrochar/nickel. Another explanation for this was the difference in graphitization degree of these samples. The graphitic structures of carbons, size effects, uniformity and content of nickel particles may be used to explain the capacity changes. Taking into account the impact of these factors, it is not surprising that the amount of the increase in capacitance of activated carbon/nickel was less than hydrochar/nickel.
-0.4
4. Conclusions -0.8 -1.2 0
50
100
150
200
Time(s) Fig. 3. (A) XRD patterns, (B) CV curves, and (C) Galvanostatic charging/discharging curves of the (a) hydrochar, (b) hydrochar/Ni, (c) activated carbon, and (d) activated carbon/Ni.
the amorphous carbon, leaving behind a track of graphitic carbon in accordance with a dissolution–precipitation mechanism [15]. In the following carbonthermal reduction reaction, the activated carbon did not have so many functional groups to interact with nickelous acetate, which was not conducive to the formation of nickel to some extent. This may be a reason for a large number of nickel (30.3 wt.%) presented on the surface of hydrochar, but only a small content of nickel (2.6 wt.%) loaded on the activated carbon under the same preparation conditions. The huge difference in nickel content between hydrochar and activated carbon indicated the formation of hydrochar/nickel more easily than activated carbon/nickel composite, which was consistent with Fig. 2b and d, uniform and more nickel dispersed on the hydrochar.
3.3. Electrochemical properties The electrochemical properties of these materials were investigated by CV and galvanostatic charge/discharge techniques. Fig. 3B showed the CV curves at the scan rates of 10 mV s− 1. The four curves presented similar rectangular shape, which indicated the capacitive behaviors of
In summary, the new electrode material hydrochar/nicke composite based on rice husk was prepared by a series of processes, including hydrothermal reaction, chemical precipitation and thermal annealing. This method, which was easy to load nickel on carbon, can be applied in fabrication of other metals and hydrochar composites. The specific capacity of the hydrochar had been effectively improved by 149% through the function of nickel. The hydrochar/nickel showed a specific capacitance of 174.5 F g − 1. This work laid the foundation for the further exploration of ways to improve the capacity of hydrochar. The applications of hydrochar and metal composites are not limited to the capacitor electrodes, they also can be applied to other energy storage devices (such as lithium ion battery), catalytic materials, magnetic materials and so on. Acknowledgments This research work was supported by the Key Project of the National Eleventh Five-Year Research Program of China (2008BAE66B00), Scientific and Technological Planning Project of Jilin Province (20075009 and 20100326) and Interdisciplinary Research Project of Jilin University (201003030). References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Yuan G, Jiang Z, Aramata A, Gao Y. Carbon 2005;43:2913. Zhang LL, Zhao XS. Chem Soc Rev 2009;38:2520. Simon P, Gogotsi Y. Nat Mater 2008;7:852. Subramanian V, Hall SC, Smith PH, Rambabu B. Solid State Ion 2004;175:511. Frackowiak E. Phys Chem Chem Phys 2007;9:1874. Wang K, Huang J, Wei Z. J Phys Chem C 2010;114:8062. Liu XM, Zhang XG, Fu SH. Mater Res Bull 2006;41:620. Deng JJ, Deng JC, Liu ZH, Deng HR, Liu B. J Mater Sci 2009;44:2828. Guo HY, Zhao HJ, Akiko A, Gao YZ. Carbon 2005;43:2913–7.
114 [10] [11] [12] [13]
L. Ding et al. / Materials Letters 74 (2012) 111–114 Lee JY, Liang K, An KH, Lee YH. Synth Mat 2005;150:153. Wang L, Guo Y, Zhu Y, Li Y, Qu Y, Rong C. Bioresour Technol 2010;101:9808. Wang L, Guo Y, Zou B, Li Y, Rong C, Ma X, et al. Bioresour Technol 2011;102:1947–50. Wang L, Wang X, Zou B, Ma X, Qu Y, Rong C, et al. Bioresour Technol 2011;102: 8220–4.
[14] [15] [16] [17]
Lou XW, Chen JS, Chen P, Archer LA. Chem Mater 2009;21:2872. Sevilla M, Fuertes AB. Mater Chem Phys 2009;113:208–14. Wu X, Jiang LY, Cao FF, Guo YG, Wan LJ. Adv Mater 2009;21:2710–4. Balaya P. Energy Environ Sci 2008;1:645–54.