·联系方式
·关于我们
·学会信箱
·设为首页
  首 页 科技前沿 装备技术 今日关注 会展快讯 学术时空 供需交流 知识之窗 金属学会
 
 

石墨烯/聚苯胺纳米复合材料作为高性能超级电容器电极材料

2014-5-27 9:14:06

李靖,谢华清,黎阳,王继芬
 
(上海第二工业大学城市建设与环境工程学院)
 
摘要:利用原位聚合法在苯胺单体中合成了石墨烯与聚苯胺纳米纤维的复合材料。利用扫描电镜(SEM)、透射电镜(TEM)和X-射线衍射(XRD)对合成材料的形貌和结构进行了表征,利用循环伏安法和恒电流充放电测试技术对合成材料的电化学性能进行了分析。直径为40 nm的聚苯胺纳米纤维分散在石墨烯表面。放电电流2 A/g时,石墨烯/聚苯胺纳米复合材料在1 mol/LH2SO4溶液中的比电容为994 F/g,显著高于石墨烯(320 F/g)和聚苯胺的比电容(210 F/g)。复合材料优异的超级电容性能不仅在于石墨烯可以为苯胺成核提供更多的活性中心,同时聚苯胺具有非常好的电化学活性。石墨烯/聚苯胺纳米复合材料具有长时间的循环寿命,1000次充放电后,复合材料的比电容下降到初始值的11%,聚苯胺的比电容在1000次充放电后下降到初始值的28%。石墨烯/聚苯胺纳米复合材料是一种性能优良的电化学储能器件电极材料。
关键词:石墨烯,聚苯胺,超级电容器,复合材料
 
Fabrication of Graphene/Polyaniline Composite for High-Performance Supercapacitor Electrode
Jing Li, Huaqing Xie*, Yang Li, Jifen Wang
School of Urban Development and Environmental Engineering, Shanghai Second Polytechnic University
  
Abstract: Composite films of graphene and polyaniline nanofibers are prepared by in situ polymerization of aniline monomer in graphene suspension. The morphology and microstructure of samples are examined by scanning electron microscopy (SEM), transition electron microscopy (TEM), and X-ray diffraction (XRD). Electrochemical performances are characterized by cyclic voltammetry (CV) and galvanostatic charge/discharge measurements. Graphene is homogeneously coated by polyaniline nanofibers with diameter of 40 nm. Supercapacitors based on the graphene/polyaniline conductive composite films exhibit large electrochemical capacitance (994 F/g) at a discharge rate of 2.0 A/g in 1 M H2SO4 solution, which is much higher than the graphene (320 F/g) and polyaniline electrode (210 F/g). The excellent performance is not only due to the graphene which can provide more active sites for nucleation of polyaniline, but also associated with a good redox activity of ordered polyaniline nanofibers. Moreover, the composite films exhibit excellent long cycle life during charge/discharge processes. After 1000 cycles, the specific capacitance decreases 11% of initial capacitance compared to 28% for polyaniline nanofibers. The resulting composite is a promising electrode material for high-performance electrical energy storage devices.
Keywords: Graphene, Polyaniline, Supercapacitor, Composite
 
1. Introduction
      Graphene, a two-dimensional monolayer of sp2-bonded carbon atoms, has attracted tremendous attention in recent years [1]. Due to its intriguing electronic properties, graphene is considered as outstanding electrode material for supercapacitors [2]. The synthesis of graphene by either chemical reduction or thermal reduction of graphene oxide usually results agglomeration of graphene sheets and decreases the specific capacitance [3].
Low cost of conducting polymers, like polyaniline (PANI), is also widely used as electrode material for supercapacitor because of its excellent capacity for energy storage, easy synthesis, and good environmental stability [4]. However, PANI is susceptible to rapid degradation in performance upon repetitive cycles. Thus, various porous carbon materials were usually used as additives for fabricating PANI-based electrodes [5, 6]. The combination of PANI with carbon materials has been proved to reinforce the stability of PANI as well as maximize the value of capacitance [7]. The combination of graphene and PANI may open the opportunity to prepare high performance supercapacitor electrode [8].
In this work, composite of graphene and PANI nanofibers is synthesized using HCl as dopant. The introduction of amounts of graphene into PANI could greatly enhance the electrochemical performances of composite. The graphene/PANI composite exhibits large specific capacitance and excellent long-term cycle stability.
 
2. Experimental details
      Graphene oxide (GO) was synthesized using natural graphite by the modified Hummers method [9]. Graphene was prepared by the reduction of GO with hydrazine hydrate as described elsewhere [10]. Composite of graphene/PANI was synthesized by in situ polymerization of aniline monomer in HCl solution. First, the purified aniline (6 mmol) was added into 50 mL of graphene suspension (3 mg/mL). The mixture of aniline and graphene was obtained after ultrasonicated for 1 h. While maintaining vigorous stirring, ammonium persulfate (APS, 1.5 mmol) in 50 mL of 2 M HCl was rapidly poured into the above mixture. Then the reaction was allowed to stir overnight. The composite was collected by filtration and repetitively washed with distilled water until the filtrate became colorless, dried at 60 oC for 12 h in a vacuum oven. For comparison, pure PANI was also synthesized through the above mentioned chemical process without the presence of graphene.
A glassy carbon electrode (GCE, Φ4mm) was used as substrate to evaluate the capacitance of samples. The basal GCE was polished to a mirror finish using alumina slurries with different powder size down to 0.05 μm. Then the GCE was sonicated in ethanol and deionized water for 5 min, successively. The fabrication of working electrode was carried out as follows. Briefly, 10 mg of the samples was dispersed in 2 mL of ethanol containing 10 μL of nafion (5 wt% in ethanol) by sonication for 30 min. 5 μL of the treated suspension was dripped onto the GCE surface, naturally dried at room temperature to form nafion-impregnated sample adsorbed GCE.
Electrochemical experiments were performed on a CHI 660C electrochemical workstation (ChenHua Instruments Co., Shanghai). A three-electrode system was used, consisting of the working electrode, platinum as the counter electrode, and a saturated calomel electrode as the reference electrode. Galvanostatic charge/discharge curves were measured using computer controlled cycling equipment (LAND, Wuhan China).
The morphologies of the samples were investigated by scanning electron microscopy S-4800 (SEM, HITACHI) and transmission electron microscopy 2100F (TEM, JEOL). XRD measurements were recorded on X-ray diffraction system (D8-Advance, Germany) equipped with Cu Kα radiationa (λ = 1.54Å).
 
3. Results and discussion
Fig. 1a shows the SEM image of pure PANI, which exhibits uniform fibrous structures of hundreds of nanometers in length and 40 nm in width. Fig. 1b presents the TEM image of graphene sheets. The corrugated and lamellar sheets resemble crumpled silk veil waves on the top of the grid. Fig. 1c draws the image of graphene/PANI composite. It is clearly observed that graphene is covered by PANI nanofibers.
Fig. 2 shows the XRD patterns of graphene, PANI, and graphene/PANI composite, respectively. Graphene exhibits a stong 002 diffraction peak at 2θ=24.1o, while the diffraction peak for GO appears at 2θ =12.1o (data was not shown). For pure PANI, the peaks appear at 19.3o and 25.2o, corresponding to 020 and 200 crystal planes of PANI in its emeraldine salt form, respectively [11]. The graphene/PANI composite presents similar peaks of pure PANI, revealing no additional crystalline order has been introduced into the composite.
The electrochemical performance of the supercapacitors electrodes were measured by cyclic voltammetry (CV) and galvanostatic charge/discharge. Fig. 3 illustrates the CV curves of graphene, PANI and graphene/PANI composite. The CVs of graphene electrode exhibit an approximately rectangular shape which is characteristic of an EDLC (curve a). For PANI (curve b) and graphene/PANI composite (curve c), there are two pairs of redox peaks (C1/A1, C2/A2), which can be ascribed to the redox transition of PANI from leucoemeraldine form to emeraldine form and faradaic transformation from emeraldine to pernigraniline [12]. It can be apparently found that the surrounded by CV curves of composite are apparently larger than that of pure PANI, indicating the higher specific capacitance.
Fig. 4 shows the galvanostatic charge/discharge curves of graphene, PANI and graphene/PANI. The graphene electrode presents a triangular-shape curve with specific capacitance of 320 F/g (curve a). For the graphene/PANI composite electrode (curve c), there are two voltage stages in the range of 0.8-0.5 V and 0.5-0 V, respectively. The former exhibits relatively short charge/discharge duration, attributed to an EDLC from the charge separation on the electrode/electrolyte interface. The latter stage is ascribed to the combination of EDLC and faradaic redox capacitance. The curves of PANI nanofibers (curve b) maintain the similar shape of the graphene/PANI composite. The specific capacitance is 210 F/g, which is much lower than the graphene/PANI electrode (994 F/g). The greatly enhanced capacitance for graphene/PANI composite is probably due to the synergetic effect between the two components. The well-ordered PANI nanofibers not only effectively inhibit the stacking/agglomerating of graphene, but also present enhanced electrode/electrolyte interface areas, improving the high electrochemical utilization of PANI and graphene.
Long cycle life is an important parameter for supercapacitor electrodes. The long-term cycle stability of graphene, PANI and graphene/PANI composite was evaluated by repeating the CV measurment from -0.2 to 1.0 V at a scan rate of 100 mV/s for 1000 cycles. The capacitance decreases only 11% of initial value for graphene/PANI electrode, in comparison of 28% for PANI, revealing graphene could improve the stability of PANI. The decrease of the capacitance probably results from swelling and shrinkage of PANI, which may lead to degradation of the conductivity and charge storage capability during charge/discharge processes.
 
4. Conclusion
Graphene/PANI composite has been synthesized using in situ polymerization of aniline using HCl as dopant in graphene suspension. The well-dispersed PANI nanofibers on graphene greatly improve the electrochemical utilization of PANI. The graphene/PANI composite electrode exhibits high specific capacitance (994 F/g) and excellent long cycle life, suggesting the graphene/PANI composite is suitable and promising electrode material for supercapacitor.
 
Acknowledgements
This work was supported by Program for New Century Excellent Talents in University (NCET-10-883), the Shanghai Municipal Education Commission and the Shanghai Educational Development Foundation (11CG64), the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, the Innovation Program of Shanghai Municipal Education Commission (12YZ179), and Fundamental and priority program of Shanghai Committee of Science and Technology (10JC1405700).
 
 
 
References
1. K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, M.I. Katsnelson, S.V. Dubonos Nature 438, 197 (2005)
2. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, Dubonos SV, I.V. Grigorieva and A.A. Firsov, Science 306, 666 (2004)
3. M. D. Stoller, S. J. Park, Y. W. Zhu, J. H. An and R. S. Ruoff, Nano Lett., 8, 3498 (2008)
4. R. H. Lee, H. H. Lai, J. J. Wang, R. J. Jeng and J. J. Lin, Thin Solid Films 517, 500 (2008)
5. J. Jang, J. Bae, M. Choi and S. H. Yoon, Carbon 43, 2730 (2005)
6. L. X. Li, H. H. Song, Q. C. Zhang, J. Y. Yao and X. H. Chen, J. Power Sources 187, 268 (2009)
7. H.Y. Mi, X.G. Zhang, S.Y. An, X.G. Ye, S.D. Yang, Electrochem. Commun. 9, 2859 (2007)
8. L. L. Zhang, R. Zhou and X. S. Zhao, J. Mater. Chem. 20, 5983 (2010)
9. W. S. Hummers and R. E. Offeman, J. Am. Chem. Soc. 80, 1339 (1958)
10. S. Stankovich, D. A. Dikin, R. D. Piner, K. A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S. T. Nguyen and R. S. Ruoff, Carbon 45, 1558 (2007)
11. M. Deka, A.K. Nath, A. Kumar, J. Membrane Sci. 327, 188 (2009)
12. Y.G. Wang, H.Q. Li, Y.Y. Xia, Adv. Mater. 18, 2619 (2006)
 
 




上一篇: TiO2/氮掺杂碳纳米管复合材料的制备及光催化性能的提高 [2014/5/22]   下一篇: 低碳中锰(0.2C-7Mn)钢奥氏体逆转变过程中的组织和性能 [2014/5/29]

 
发布评论
用户名: 密码: 验证码: 点击更换 注册


上海市科学技术委员会 | 上海市科技协会 | 中国金属学会 | 中国钢铁工业协会 | 上海有色金属协会 | 上海技术服务网 | 东方科技论坛 | 上海民间组织 | 钢材价格
版权所有 上海金属学会 (C)2007 All Rights Reserved.
地址:上海市南昌路47号3号楼3309室 电话:(021)53821027  
上海钢联电子商务有限公司 设计制作 沪ICP备06014293号