- Email: [email protected]
polypyrrole electrodes for supercapacitors
Solid State Communications 197 (2014) 57–60
Contents lists available at ScienceDirect
Solid State Communications journal homepage: www.elsevier.com/locate/ssc
Preparation and characterization of RuO2/polypyrrole electrodes for supercapacitors Xiang Li a,n, Yujiao Wu a, Feng Zheng b, Min Ling a, Fanghai Lu a a b
School of Material and Metallurgical Engineering, Guizhou Institute of Technology, Guiyang 550003, China School of Material Science and Engineering, Central South University, Changsha 410083, China
art ic l e i nf o
a b s t r a c t
Article history: Received 4 November 2013 Received in revised form 25 July 2014 Accepted 27 July 2014 by V. Pellegrini Available online 2 August 2014
Polypyrrole (PPy) embedded RuO2 electrodes were prepared by the composite method. Precursor solution of RuO2 was coated on tantalum sheet and annealed at 260 1C for 2.5 h to develop a thin film. PPy particles were deposited on RuO2 films and dried at 80 1C for 12 h to form composite electrode. Microstructure and morphology of RuO2/PPy electrode were characterized using Fourier transform infrared spectrometer, X-ray diffraction and scanning electron microscopy, respectively. Our results confirmed that counter ions are incorporated into RuO2 matrix. Structure of the composite with amorphous phase was verified by X-ray diffraction. Analysis by scanning electron microscopy reveals that during grain growth of RuO2/PPy, PPy particle size sharply increases as deposition time is over 20 min. Electrochemical properties of RuO2/PPy electrode were calculated using cyclic voltammetry. As deposition times of PPy are 10, 20, 25 and 30 min, specific capacitances of composite electrodes reach 657, 553, 471 and 396 F g 1, respectively. Cyclic behaviors of RuO2/PPy composite electrodes are stable. & 2014 Elsevier Ltd. All rights reserved.
Keywords: B. Ruthenium oxide B. Polypyrrole B. Electrodeposition B. Specific capacitance
1. Introduction Electrochemical capacitor or supercapacitor is known to store energy by two different mechanisms. The first is associated with separation of electronic and ionic charges at electrode/electrolyte interface and is named as the double-layer capacitors. The second involves absorption or insertion of electro-active species into solid phase accompanied by charge transfer processes, and is named pseudocapacitors [1–4]. Electrode material is critical to determine performances of supercapacitors. Thus, it is important to develop electrode materials. At present, many transition metal oxides such as RuO2, MnO2, and NiO2 [5–10] and conducting polymers have been examined as electrode materials for Faradaic pseudocapacitors [11]. Specific capacitance of RuO2 can reach 768 F g 1 [5]. However, RuO2 has many disadvantages such as high cost, low porosity and rapid decay of power density at high charge and discharge rates. Meanwhile, specific capacitance of MnO2 or NiO2 is relative low. In contrast to transition metal oxides, conducting polymers have been considered as potential choices for electrode materials. In recent years, polypyrrole (PPy), an important conducting polymer, has been successfully employed as redox electrode material [12–14]. The specific capacitance of PPy has been measured to be 180–250 F g 1 [15–17]. In spite of its high charge
n
Corresponding author. Tel.: þ 86 851 8210967; fax: þ 86 851 8210967. E-mail address: [email protected] (X. Li).
http://dx.doi.org/10.1016/j.ssc.2014.07.019 0038-1098/& 2014 Elsevier Ltd. All rights reserved.
storage capacitance, PPy and other conducting polymers lack in long-term stability [18]. Thus the objective of this paper is to combine the high specific capacitance of RuO2 with low cost of PPy in order to make beneficial use of both materials. To further improve capacitance and cyclic stability of RuO2/PPy electrode, RuO2 will be coated on tantalum sheet and used as matrix to embed PPy particles.
2. Experimental procedures 2.1. Materials and reagents Tantalum (99.95 wt%) sheet was used as substrate due to its high conduction and corrosion resistance. Commercial pyrrole was purified before use. Deionized water of 18 MΩ was obtained from an aqua system (KL-UP-II-20). Ruthenium chloride (RuCl3. nH2O), and other chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd. with further modification. 2.2. Preparation of RuO2 electrode Tantalum sheet (∅27 mm) was polished by abrasive paper and rinsed with acid in an ultrasonic bath. Precursor solution of RuO2 was prepared by the addition of RuCl3 xH2O to isopropyl alcohol under stirring at 25 1C for 0.5 h. After that, the precursor solution
58
X. Li et al. / Solid State Communications 197 (2014) 57–60
was coated onto tantalum substrate and annealed at 260 1C for 2.5 h. 2.3. Preparation of RuO2/PPy electrode Pyrrole monomers (0.1 M) in 0.5 M H2SO4 water solution were used for growth of polymer particles. PPy particles were electrochemically deposited on RuO2 films under galvanostatic conditions by applying constant current density (2 mA cm 1) for fixed durations of 10, 20, 25 and 30 s. These electrodes were rinsed in deionized water and dried at 80 1C for 12 h prior to electrochemical measure evaluation. 2.4. Instrumentation RuO2/PPy electrode was weighed using digital balance (Shimadzu corporation type AW220) with sensitivity of 0.01 mg. Values of specific capacitance were calculated based on total mass of activated materials on tantalum working electrode. Fourier transform infrared (FTIR) measurements (Nicolet 6700) were performed in the wavelength range of 4000–400 cm 1 with the KBr pellet method. Morphologies of RuO2/PPy electrodes were analyzed by Sirion 200 scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Microstructures of as-prepared samples were analyzed by X-ray diffraction (Rigaku 2500) with Cu kα radiation at a scan rate of 0.33 s covering 10–801. Electrochemical measurements were carried out in a three electrode electrochemical work station (IM6ex). A platinum electrode was used as auxiliary electrode. All potentials were measured versus Hg/Hg2SO4 reference electrode. Cyclic voltammetry (CV) and charge–discharge experiment were performed in 0.5 M H2SO4 electrolyte.
3. Results and discussions Existence of RuO2/PPy in as-prepared sample was confirmed by FTIR, as shown in Fig. 1. The broad band at 3439.82 cm 1 is assigned to –OH stretching vibration. This bond may be attributed to the adsorbed water inside pores of RuO2/PPy. In addition, hydrogen bonds may come into play. The 2922.46 and 2852.25 cm 1 absorption bands belong to CH3- and CH2-stretching vibration, respectively. The band (1642.90 cm 1) is assigned to the stretching vibration of aromatic rings. Vibrations between 1456.02 and 1399.97 cm 1 originate from absorption of CH2scissor. The 1061.09 cm 1 absorption band illustrates C–N stretching vibration. In addition, the 490.73 cm 1 band indicates Ru–N stretching vibration. FITR spectroscopy results confirm that counter ion has been incorporated into PPy matrix. This illustrates that
Fig. 2. XRD patterns of RuO2/PPy composite annealed at 260 1C for 2.5 h.
H2SO4 and LiClO4 acted as the dopant in the electrochemical polymerization of pyrrole. XRD pattern of RuO2/PPy sample is shown in Fig. 2. For RuO2/ PPy composite, relative two broad peaks (38.11and 43.61) reveal the existence of amorphous phase. Meanwhile, a few low diffraction peaks were observed. A possible explanation for this fact can be related to the preparation of composite electrode [19]. Calcination of electrode was accomplished in air. As this process started from surface, owing to availability of oxygen, the oxygen partial pressure inside the sample was sufficient to oxidize the organic portion into CO. Then, CO reacted with Ru ions to reduce them into metallic state. SEM images of as-prepared electrode samples at different deposition times (10, 20, 25 and 30 min) are shown in Fig. 3. Cracks in electrode are presented in Fig. 3a. Morphology of electrode, as is shown in Fig. 3b, indicates that size of PPy particles has increased to some degree. Cracks were formed during RuO2 film preparation, and there is no direct correlation between the amount of PPy and cracks. Once PPy particles went through growth, they filled into and eliminated those cracks. As can be seen from Fig. 3c, a large number of PPy particles deposited on RuO2 film. Meanwhile, the size of small particle in agglomeration is about1.0–1.5 μm in diameter. Fig. 3d shows image of PPy particles fully covering the RuO2 film surface with agglomeration size of 1.2–2.5 μm. According to the discussion mentioned above, PPy particles grow slowly for the first 20 min during deposition and then go through rapid growth afterwards. Cyclic voltammetry (CV) curves of RuO2/PPy electrode prepared at different deposition times (10, 20, 25 and 30 min) are displayed in Fig. 4. Note, there is no clear redox peaks and all CV curves indicate a typical capacitive behavior. This is because of the charge and discharge process of PPy conducting polymer and pseudocapacitive behaviors. The CV measurements were carried out in 0.5 M H2SO4 solution at a potential range from –0.6 to 0.6 V and at a scan rate of 50 mV s 1. Specific capacitance is obtained from CV curves with the equation: Cs ¼
Fig. 1. FI-IR spectra of RuO2/PPy composite.
i mv
where C s is the specific capacitance in F g 1, i is the average current, v is the potential sweep rate in mV s 1, and m is the mass of activated materials in g. Average specific capacitances of 657, 553, 471 and 396 F g 1, respectively, are obtained at different deposition times (10, 20, 25 and 30 min). Galvanostatic charge and discharge for RuO2/PPy electrodes were carried at 30 mA. Chronopotentiograms of composite electrodes with different deposition times (10, 20, 25 and 30 min) are shown as curves 1–4 in Fig. 5, correspondingly. From curve 1, iR (voltage drop) is about 37.3 mV. Through calculation (R¼V/i), resistance of curve 1 is about 1.23 Ω. Meanwhile, charge curve is
X. Li et al. / Solid State Communications 197 (2014) 57–60
59
Fig. 3. SEM images of growth for PPy particles covering RuO2 films after different deposition times: (a) 10 min, (b) 20 min, (c) 30 min and (d) 40 min.
Fig. 4. Cyclic voltammograms (CV) of RuO2/PPy composite with 10, 20, 25 and 30 min deposition times. CV curves were measured in 0.5 M H2SO4 electrolyte at 50 mV s 1 scan rate.
symmetric to its discharge counterpart. However, discharge time is relatively short. Similarly, resistances of curves 2, 3 and 4 are 1.54, 1.64 and 1.78 Ω, respectively. In addition, curves 3 and 4 have long discharge time compared with those of 1 and 2. Although specific capacitance of composite electrode has decreased, its capacitance
Fig. 5. Chronopotentiograms of RuO2/PPy composite with 10, 20, 25 and 30 min deposition times. CPs was measured at 30 mA in 0.5 M H2SO4.
has increased instead. Based on former discussion, we know that the capacitance of RuO2/PPy electrode increased with the growth of PPy particles with relatively low resistance. The stability of RuO2/PPy electrodes with different deposition times (10, 20, 25 and 30 min) was measured by cycle life test. The variation of specific capacitance as a function of cycle number is shown in Fig. 6. Based on Fig. 6, we can calculate the decay rate of
60
X. Li et al. / Solid State Communications 197 (2014) 57–60
particles have covered RuO2 films. PPy particle size increases sharply once deposition time is over 20 min. CV curves of RuO2/ PPy electrode with different deposition times (10, 20, 25 and 30 min) showed ideal capacitive behaviors. Specific capacitances of 657, 553, 471 and 396 F g 1 are obtained as deposition times are 10, 20, 25, 30 min, respectively. Charge and discharge property of RuO2/PPy electrode is good. After 1000 cycles, nearly 3.4%, 4.5%, 5.9% and 7.5% decay in capacity value are observed. Composite electrode is very stable. References
Fig. 6. Cycling behaviors of RuO2/PPy composite electrodes. Scan rate: 50 mV s 1 in 0.5 M H2SO4 electrolyte.
capacity for curves 1–4, after 1000 cycles, to be roughly 3.4%, 4.5%, 5.9% and 7.5%, correspondingly. These results indicate that our composite electrodes are very stable.
[1] [2] [3] [4] [5] [6]
4. Conclusions
[7] [8] [9] [10] [11] [12]
Amorphous RuO2/PPy electrodes were prepared by thermal decomposition oxidation and electrodeposition. XRD results confirmed that RuO2/PPy electrode is amorphous. Fourier transform infrared spectrometer results confirmed that counter ions are incorporated into RuO2 matrix. SEM images indicated that PPy
[13] [14] [15] [16] [17] [18] [19]
A. Burke, Electrochim. Acta 53 (2007) 1083. A.G. Pandolfo, A.E. Hollenkamp, J. Power Sour. 157 (2006) 11. R. Kotz, M. Carlen, Electrochim. Acta 45 (2000) 2483. M. Mastragostino, F. Soavi, J. Power Sour. 174 (2007) 89. J.P. Zheng, T.R. Jow, J. Electrochem. Soc. 142 (1995) 2699. H. Xia, Y.S. Meng, G.L. Yuan, C. Cui, L.i. Lu, Electrochem. Solid-State Lett. 15 (2012) A60. Y.G. Wang, Z.D. Wang, Y.Y. Xia, Electrochim. Acta 50 (2005) 5641. H. Xia, W. Xiao, M.Q. Lai, L. Lu, Nanoscale Res. Lett. 4 (2009) 1035. V. Subramanian, H.W. Zhu, B.Q. Wei, J. Power Sour. 159 (2006) 361. L. Chuan, A. James, N.J. Branko, J. Electrochem. Soc. 145 (1998) 4097. G.A. Snook, P. Kao, A.S. Best, J. Power Sour. 196 (2011) 1. X. Li, W.P. Gan, F. Zheng, L.L. Li, N.N. Zhu, X.Q. Huang, Synth. Met. 162 (2012) 953. L.Z. Fan, J. Maier, Electrochem. Commun. 8 (2006) 93. C.M. Li, C.Q. Sun, W. Chenl, Surf. Coat. Technol. 198 (2005) 474. D.P. Dubal, S.V. Patil, W.B. Kim, Mater. Lett. 6 (2011) 2628. R.K. Sharma, A.C. Rastogi, S.B. Desu, Electrochem. Commun. 10 (2008) 268. Y.J. Wang, C. Yang, P. Liu, Chem. Eng. J. 172 (2011) 1137. D.C. Zhang, X. Zhang, Y. Chenl, J. Power Sour. 196 (2011) 5990. V. Adriane, L.O.S. Bulhoes, J. Power Sour. 158 (2006) 799.
Contents lists available at ScienceDirect
Solid State Communications journal homepage: www.elsevier.com/locate/ssc
Preparation and characterization of RuO2/polypyrrole electrodes for supercapacitors Xiang Li a,n, Yujiao Wu a, Feng Zheng b, Min Ling a, Fanghai Lu a a b
School of Material and Metallurgical Engineering, Guizhou Institute of Technology, Guiyang 550003, China School of Material Science and Engineering, Central South University, Changsha 410083, China
art ic l e i nf o
a b s t r a c t
Article history: Received 4 November 2013 Received in revised form 25 July 2014 Accepted 27 July 2014 by V. Pellegrini Available online 2 August 2014
Polypyrrole (PPy) embedded RuO2 electrodes were prepared by the composite method. Precursor solution of RuO2 was coated on tantalum sheet and annealed at 260 1C for 2.5 h to develop a thin film. PPy particles were deposited on RuO2 films and dried at 80 1C for 12 h to form composite electrode. Microstructure and morphology of RuO2/PPy electrode were characterized using Fourier transform infrared spectrometer, X-ray diffraction and scanning electron microscopy, respectively. Our results confirmed that counter ions are incorporated into RuO2 matrix. Structure of the composite with amorphous phase was verified by X-ray diffraction. Analysis by scanning electron microscopy reveals that during grain growth of RuO2/PPy, PPy particle size sharply increases as deposition time is over 20 min. Electrochemical properties of RuO2/PPy electrode were calculated using cyclic voltammetry. As deposition times of PPy are 10, 20, 25 and 30 min, specific capacitances of composite electrodes reach 657, 553, 471 and 396 F g 1, respectively. Cyclic behaviors of RuO2/PPy composite electrodes are stable. & 2014 Elsevier Ltd. All rights reserved.
Keywords: B. Ruthenium oxide B. Polypyrrole B. Electrodeposition B. Specific capacitance
1. Introduction Electrochemical capacitor or supercapacitor is known to store energy by two different mechanisms. The first is associated with separation of electronic and ionic charges at electrode/electrolyte interface and is named as the double-layer capacitors. The second involves absorption or insertion of electro-active species into solid phase accompanied by charge transfer processes, and is named pseudocapacitors [1–4]. Electrode material is critical to determine performances of supercapacitors. Thus, it is important to develop electrode materials. At present, many transition metal oxides such as RuO2, MnO2, and NiO2 [5–10] and conducting polymers have been examined as electrode materials for Faradaic pseudocapacitors [11]. Specific capacitance of RuO2 can reach 768 F g 1 [5]. However, RuO2 has many disadvantages such as high cost, low porosity and rapid decay of power density at high charge and discharge rates. Meanwhile, specific capacitance of MnO2 or NiO2 is relative low. In contrast to transition metal oxides, conducting polymers have been considered as potential choices for electrode materials. In recent years, polypyrrole (PPy), an important conducting polymer, has been successfully employed as redox electrode material [12–14]. The specific capacitance of PPy has been measured to be 180–250 F g 1 [15–17]. In spite of its high charge
n
Corresponding author. Tel.: þ 86 851 8210967; fax: þ 86 851 8210967. E-mail address: [email protected] (X. Li).
http://dx.doi.org/10.1016/j.ssc.2014.07.019 0038-1098/& 2014 Elsevier Ltd. All rights reserved.
storage capacitance, PPy and other conducting polymers lack in long-term stability [18]. Thus the objective of this paper is to combine the high specific capacitance of RuO2 with low cost of PPy in order to make beneficial use of both materials. To further improve capacitance and cyclic stability of RuO2/PPy electrode, RuO2 will be coated on tantalum sheet and used as matrix to embed PPy particles.
2. Experimental procedures 2.1. Materials and reagents Tantalum (99.95 wt%) sheet was used as substrate due to its high conduction and corrosion resistance. Commercial pyrrole was purified before use. Deionized water of 18 MΩ was obtained from an aqua system (KL-UP-II-20). Ruthenium chloride (RuCl3. nH2O), and other chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd. with further modification. 2.2. Preparation of RuO2 electrode Tantalum sheet (∅27 mm) was polished by abrasive paper and rinsed with acid in an ultrasonic bath. Precursor solution of RuO2 was prepared by the addition of RuCl3 xH2O to isopropyl alcohol under stirring at 25 1C for 0.5 h. After that, the precursor solution
58
X. Li et al. / Solid State Communications 197 (2014) 57–60
was coated onto tantalum substrate and annealed at 260 1C for 2.5 h. 2.3. Preparation of RuO2/PPy electrode Pyrrole monomers (0.1 M) in 0.5 M H2SO4 water solution were used for growth of polymer particles. PPy particles were electrochemically deposited on RuO2 films under galvanostatic conditions by applying constant current density (2 mA cm 1) for fixed durations of 10, 20, 25 and 30 s. These electrodes were rinsed in deionized water and dried at 80 1C for 12 h prior to electrochemical measure evaluation. 2.4. Instrumentation RuO2/PPy electrode was weighed using digital balance (Shimadzu corporation type AW220) with sensitivity of 0.01 mg. Values of specific capacitance were calculated based on total mass of activated materials on tantalum working electrode. Fourier transform infrared (FTIR) measurements (Nicolet 6700) were performed in the wavelength range of 4000–400 cm 1 with the KBr pellet method. Morphologies of RuO2/PPy electrodes were analyzed by Sirion 200 scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Microstructures of as-prepared samples were analyzed by X-ray diffraction (Rigaku 2500) with Cu kα radiation at a scan rate of 0.33 s covering 10–801. Electrochemical measurements were carried out in a three electrode electrochemical work station (IM6ex). A platinum electrode was used as auxiliary electrode. All potentials were measured versus Hg/Hg2SO4 reference electrode. Cyclic voltammetry (CV) and charge–discharge experiment were performed in 0.5 M H2SO4 electrolyte.
3. Results and discussions Existence of RuO2/PPy in as-prepared sample was confirmed by FTIR, as shown in Fig. 1. The broad band at 3439.82 cm 1 is assigned to –OH stretching vibration. This bond may be attributed to the adsorbed water inside pores of RuO2/PPy. In addition, hydrogen bonds may come into play. The 2922.46 and 2852.25 cm 1 absorption bands belong to CH3- and CH2-stretching vibration, respectively. The band (1642.90 cm 1) is assigned to the stretching vibration of aromatic rings. Vibrations between 1456.02 and 1399.97 cm 1 originate from absorption of CH2scissor. The 1061.09 cm 1 absorption band illustrates C–N stretching vibration. In addition, the 490.73 cm 1 band indicates Ru–N stretching vibration. FITR spectroscopy results confirm that counter ion has been incorporated into PPy matrix. This illustrates that
Fig. 2. XRD patterns of RuO2/PPy composite annealed at 260 1C for 2.5 h.
H2SO4 and LiClO4 acted as the dopant in the electrochemical polymerization of pyrrole. XRD pattern of RuO2/PPy sample is shown in Fig. 2. For RuO2/ PPy composite, relative two broad peaks (38.11and 43.61) reveal the existence of amorphous phase. Meanwhile, a few low diffraction peaks were observed. A possible explanation for this fact can be related to the preparation of composite electrode [19]. Calcination of electrode was accomplished in air. As this process started from surface, owing to availability of oxygen, the oxygen partial pressure inside the sample was sufficient to oxidize the organic portion into CO. Then, CO reacted with Ru ions to reduce them into metallic state. SEM images of as-prepared electrode samples at different deposition times (10, 20, 25 and 30 min) are shown in Fig. 3. Cracks in electrode are presented in Fig. 3a. Morphology of electrode, as is shown in Fig. 3b, indicates that size of PPy particles has increased to some degree. Cracks were formed during RuO2 film preparation, and there is no direct correlation between the amount of PPy and cracks. Once PPy particles went through growth, they filled into and eliminated those cracks. As can be seen from Fig. 3c, a large number of PPy particles deposited on RuO2 film. Meanwhile, the size of small particle in agglomeration is about1.0–1.5 μm in diameter. Fig. 3d shows image of PPy particles fully covering the RuO2 film surface with agglomeration size of 1.2–2.5 μm. According to the discussion mentioned above, PPy particles grow slowly for the first 20 min during deposition and then go through rapid growth afterwards. Cyclic voltammetry (CV) curves of RuO2/PPy electrode prepared at different deposition times (10, 20, 25 and 30 min) are displayed in Fig. 4. Note, there is no clear redox peaks and all CV curves indicate a typical capacitive behavior. This is because of the charge and discharge process of PPy conducting polymer and pseudocapacitive behaviors. The CV measurements were carried out in 0.5 M H2SO4 solution at a potential range from –0.6 to 0.6 V and at a scan rate of 50 mV s 1. Specific capacitance is obtained from CV curves with the equation: Cs ¼
Fig. 1. FI-IR spectra of RuO2/PPy composite.
i mv
where C s is the specific capacitance in F g 1, i is the average current, v is the potential sweep rate in mV s 1, and m is the mass of activated materials in g. Average specific capacitances of 657, 553, 471 and 396 F g 1, respectively, are obtained at different deposition times (10, 20, 25 and 30 min). Galvanostatic charge and discharge for RuO2/PPy electrodes were carried at 30 mA. Chronopotentiograms of composite electrodes with different deposition times (10, 20, 25 and 30 min) are shown as curves 1–4 in Fig. 5, correspondingly. From curve 1, iR (voltage drop) is about 37.3 mV. Through calculation (R¼V/i), resistance of curve 1 is about 1.23 Ω. Meanwhile, charge curve is
X. Li et al. / Solid State Communications 197 (2014) 57–60
59
Fig. 3. SEM images of growth for PPy particles covering RuO2 films after different deposition times: (a) 10 min, (b) 20 min, (c) 30 min and (d) 40 min.
Fig. 4. Cyclic voltammograms (CV) of RuO2/PPy composite with 10, 20, 25 and 30 min deposition times. CV curves were measured in 0.5 M H2SO4 electrolyte at 50 mV s 1 scan rate.
symmetric to its discharge counterpart. However, discharge time is relatively short. Similarly, resistances of curves 2, 3 and 4 are 1.54, 1.64 and 1.78 Ω, respectively. In addition, curves 3 and 4 have long discharge time compared with those of 1 and 2. Although specific capacitance of composite electrode has decreased, its capacitance
Fig. 5. Chronopotentiograms of RuO2/PPy composite with 10, 20, 25 and 30 min deposition times. CPs was measured at 30 mA in 0.5 M H2SO4.
has increased instead. Based on former discussion, we know that the capacitance of RuO2/PPy electrode increased with the growth of PPy particles with relatively low resistance. The stability of RuO2/PPy electrodes with different deposition times (10, 20, 25 and 30 min) was measured by cycle life test. The variation of specific capacitance as a function of cycle number is shown in Fig. 6. Based on Fig. 6, we can calculate the decay rate of
60
X. Li et al. / Solid State Communications 197 (2014) 57–60
particles have covered RuO2 films. PPy particle size increases sharply once deposition time is over 20 min. CV curves of RuO2/ PPy electrode with different deposition times (10, 20, 25 and 30 min) showed ideal capacitive behaviors. Specific capacitances of 657, 553, 471 and 396 F g 1 are obtained as deposition times are 10, 20, 25, 30 min, respectively. Charge and discharge property of RuO2/PPy electrode is good. After 1000 cycles, nearly 3.4%, 4.5%, 5.9% and 7.5% decay in capacity value are observed. Composite electrode is very stable. References
Fig. 6. Cycling behaviors of RuO2/PPy composite electrodes. Scan rate: 50 mV s 1 in 0.5 M H2SO4 electrolyte.
capacity for curves 1–4, after 1000 cycles, to be roughly 3.4%, 4.5%, 5.9% and 7.5%, correspondingly. These results indicate that our composite electrodes are very stable.
[1] [2] [3] [4] [5] [6]
4. Conclusions
[7] [8] [9] [10] [11] [12]
Amorphous RuO2/PPy electrodes were prepared by thermal decomposition oxidation and electrodeposition. XRD results confirmed that RuO2/PPy electrode is amorphous. Fourier transform infrared spectrometer results confirmed that counter ions are incorporated into RuO2 matrix. SEM images indicated that PPy
[13] [14] [15] [16] [17] [18] [19]
A. Burke, Electrochim. Acta 53 (2007) 1083. A.G. Pandolfo, A.E. Hollenkamp, J. Power Sour. 157 (2006) 11. R. Kotz, M. Carlen, Electrochim. Acta 45 (2000) 2483. M. Mastragostino, F. Soavi, J. Power Sour. 174 (2007) 89. J.P. Zheng, T.R. Jow, J. Electrochem. Soc. 142 (1995) 2699. H. Xia, Y.S. Meng, G.L. Yuan, C. Cui, L.i. Lu, Electrochem. Solid-State Lett. 15 (2012) A60. Y.G. Wang, Z.D. Wang, Y.Y. Xia, Electrochim. Acta 50 (2005) 5641. H. Xia, W. Xiao, M.Q. Lai, L. Lu, Nanoscale Res. Lett. 4 (2009) 1035. V. Subramanian, H.W. Zhu, B.Q. Wei, J. Power Sour. 159 (2006) 361. L. Chuan, A. James, N.J. Branko, J. Electrochem. Soc. 145 (1998) 4097. G.A. Snook, P. Kao, A.S. Best, J. Power Sour. 196 (2011) 1. X. Li, W.P. Gan, F. Zheng, L.L. Li, N.N. Zhu, X.Q. Huang, Synth. Met. 162 (2012) 953. L.Z. Fan, J. Maier, Electrochem. Commun. 8 (2006) 93. C.M. Li, C.Q. Sun, W. Chenl, Surf. Coat. Technol. 198 (2005) 474. D.P. Dubal, S.V. Patil, W.B. Kim, Mater. Lett. 6 (2011) 2628. R.K. Sharma, A.C. Rastogi, S.B. Desu, Electrochem. Commun. 10 (2008) 268. Y.J. Wang, C. Yang, P. Liu, Chem. Eng. J. 172 (2011) 1137. D.C. Zhang, X. Zhang, Y. Chenl, J. Power Sour. 196 (2011) 5990. V. Adriane, L.O.S. Bulhoes, J. Power Sour. 158 (2006) 799.