- Email: [email protected]
anion composites
Synthetic Metals 117 (2001) 137±139
Application of quartz crystal for the supercapacity studies of Ppy/anion composites Seong-Hun Songa, Dae-Sang Hana, Haeng-Ja Leea, Hong-Sik Choa, Sang-Mok Changa,*, Jong-Min Kimb, Horishi Muramatsub a
Department of Chemical Engineering, Dong-A University, 840 Hadan-dong, Saha-gu, Pusan 604-714, South Korea b Advanced Technology Center, Seiko Instrument Inc., Chiba 270-2222, Japan
Abstract In this work, dynamic properties of electrochemically polymerized polypyrrole in 0.1 M NaNO3 and 0.1 M NaClO4 electrolyte solution was investigated for the application of supercapacitor using piezoelectric quartz crystal. The cyclic voltammetry was performed to interpret capacitor characteristics of Ppy thin ®lm in various electrolyte solutions and the results were compared with AFM images. The results show that the perchlorate anion doped ®lms present better electrochemical capacitor characteristics than the case that other electrolytes are used as counter anions. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Polypyrrole (Ppy); Piezoelectric quartz crystal; Supercapacitor
1. Introduction Conducting polymers have received great interest as electrode matrix material because of its low material cost and high charge density [1,2]. Polypyrrole (Ppy) is well known as conducting polymer for electric double layer capacitor (EDLC) with high electric conductivity [3]. It can be easily synthesized in both aqueous and non-aqueous media by the electrochemical oxidation of the monomer. We report here the results concerning the possible use of quartz crystal for the supercapacitor studies of Ppy/anion composites. In this study, Ppy/anion composites were selected as two types of Ppy/NO3ÿ and Ppy/ClO4ÿ. AFM images were used to con®rm the results. 2. Experimental Au electrode was formed on 9 MHz, AT-cut quartz crystal by sputtering method and used as working electrode mounted on a plastic resin cell designed to expose only one side of the electrodes. The active area of working electrode is 0.2 cm2. An Ag/AgCl electrode and a Pt electrode were used as a reference and a counter electrode, respectively. *
Corresponding author.
Pyrrole was polymerized on the working electrode by the constant current density of 0.1 mA/cm2 for 180 s in 0.1 M NaNO3 and 0.1 M NaClO4 electrolyte solutions. The morphologies of the polymerized Ppy thin ®lm are imaged by AFM (SPI 3700, Seiko Instruments Inc.). Electrochemically induced dynamic changes are investigated by cyclic voltammetry with sweep range of ÿ600 to 600 mV (versus Ag/AgCl, scan rate 50 mV/s) in 0.1 M LiClO4 electrolyte solution after Ppy depositions. 3. Results and discussion Fig. 1a and b are AFM images of Ppy thin ®lms polymerized in 0.1 M NaClO4 and in 0.1 M NaNO3 solution. These AFM images indicate that the surface of Ppy thin ®lm polymerized in NaClO4 is more swelled than that of NaNO3. This fact is consistent with the result of our previous report that Ppy ®lm swells when perchlorate anion is used as dopant by anion doping and solvent transfer into the ®lm [4,5,6]. Table 1 shows one of obvious evidences that when Ppy ®lm is polymerized, especially when perchlorate anion is used, permeation is relatively bigger than other anions. In case of NO3ÿ anion, the change of resonant frequency before and after dry is only about 3 kHz. But in case of NaClO4, the change is about 17 kHz. On these simple comparisons, the solvent effect is clearly observable during the deposition
0379-6779/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 ( 0 0 ) 0 0 5 5 5 - 5
138
S.-H. Song et al. / Synthetic Metals 117 (2001) 137±139
Fig. 2. Cyclic voltammetries of Ppy films polymerized in 0.1 M NaClO4 and 0.1 M NaNO3 solution and cycled in 0.1 M LiClO4 electrolyte solution; (a) potential Ð current, (b) potential Ð frequency shift. Fig. 1. AFM images of Ppy thin films (a) polymerized in NaClO4 and (b) polymerized in NaNO3 for 180 s image areas are 2 2 mm2.
Table 1 The change of resonant frequency and admittance intensity values of Ppy/anion film before and after dry Electrolyte
Wet condition
Dry condition
Mass change (ng)
NaNO3 NaClO4 LiClO4 KClO4
8828570 Hz, 4350 mV 8796950 Hz, 1210 mV 8797072 Hz, 1420 mV 8802990 Hz, 1178 mV
8831593 Hz, 4630 mV 8814054 Hz, 4846 mV 8815370 Hz, 4665 mV 8819420 Hz, 4440 mV
2748 15549 16634 14936
processes. The water in the Ppy ®lm is very important for using the ®lm as a capacitor. As shown in Fig. 2a, Ppy thin ®lm polymerized in NaNO3 is superior in the respect of conductivity from the differences of redox peak than that in NaClO4. But for capacitor characteristics, Ppy thin ®lm polymerized in NaClO4 shows more possibility than that in NaNO3. Fig. 2b shows that frequency shift of Ppy thin ®lm polymerized in NaClO4 recovers to the initial value after one cycle of potential sweep. But the case of NaNO3 indicates the intercalation of ions about 150 Hz in Ppy ®lm. These frequency characteristics also imply the fact that Ppy thin ®lm polymerized in NaClO4 has an ideal capacitor property during redox cycle.
Acknowledgements This work was supported by the academic research fund (KRF-2000-041-E00377) of Ministry of Education, Korea and Dong-A University.
References [1] C.T. Lee, J.H. Kim, B.W. Cho, Prospect. Ind. Chem. 2 (1999) 16. [2] D.S. Gottesfeld, S. Shin, X. Ren, J. Davey, in: The 8th International Seminar on Double Layer Capacitors and Similar Energy Storage Devices, Deerfield Beach, Florida, 7±9 December 1998.
S.-H. Song et al. / Synthetic Metals 117 (2001) 137±139 [3] K. Naoi, Y. Oura, M. Maaeda, S. Nakamura, J. Electrochem. Soc. 142 (1995) 417. [4] S.M. Chang, J.M. Kim, Y.K. Chang, Y.S. Kwon, H. Muramatsu, T. Ataka, Mol. Cryst. Liq. Cryst. 280 (1996) 157.
139
[5] J.M. Kim, H.W. Lee, Y.H. Kim, Y.S. Kwon, H. Muramatsu, S.M. Chang, Mol. Cryst. Liq. Cryst. 316 (1998) 141. [6] J.M. Kim, S.M.ChangH. Muramatsu, J. Electrochem. Soc. 146 (1999) 4544.
Application of quartz crystal for the supercapacity studies of Ppy/anion composites Seong-Hun Songa, Dae-Sang Hana, Haeng-Ja Leea, Hong-Sik Choa, Sang-Mok Changa,*, Jong-Min Kimb, Horishi Muramatsub a
Department of Chemical Engineering, Dong-A University, 840 Hadan-dong, Saha-gu, Pusan 604-714, South Korea b Advanced Technology Center, Seiko Instrument Inc., Chiba 270-2222, Japan
Abstract In this work, dynamic properties of electrochemically polymerized polypyrrole in 0.1 M NaNO3 and 0.1 M NaClO4 electrolyte solution was investigated for the application of supercapacitor using piezoelectric quartz crystal. The cyclic voltammetry was performed to interpret capacitor characteristics of Ppy thin ®lm in various electrolyte solutions and the results were compared with AFM images. The results show that the perchlorate anion doped ®lms present better electrochemical capacitor characteristics than the case that other electrolytes are used as counter anions. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Polypyrrole (Ppy); Piezoelectric quartz crystal; Supercapacitor
1. Introduction Conducting polymers have received great interest as electrode matrix material because of its low material cost and high charge density [1,2]. Polypyrrole (Ppy) is well known as conducting polymer for electric double layer capacitor (EDLC) with high electric conductivity [3]. It can be easily synthesized in both aqueous and non-aqueous media by the electrochemical oxidation of the monomer. We report here the results concerning the possible use of quartz crystal for the supercapacitor studies of Ppy/anion composites. In this study, Ppy/anion composites were selected as two types of Ppy/NO3ÿ and Ppy/ClO4ÿ. AFM images were used to con®rm the results. 2. Experimental Au electrode was formed on 9 MHz, AT-cut quartz crystal by sputtering method and used as working electrode mounted on a plastic resin cell designed to expose only one side of the electrodes. The active area of working electrode is 0.2 cm2. An Ag/AgCl electrode and a Pt electrode were used as a reference and a counter electrode, respectively. *
Corresponding author.
Pyrrole was polymerized on the working electrode by the constant current density of 0.1 mA/cm2 for 180 s in 0.1 M NaNO3 and 0.1 M NaClO4 electrolyte solutions. The morphologies of the polymerized Ppy thin ®lm are imaged by AFM (SPI 3700, Seiko Instruments Inc.). Electrochemically induced dynamic changes are investigated by cyclic voltammetry with sweep range of ÿ600 to 600 mV (versus Ag/AgCl, scan rate 50 mV/s) in 0.1 M LiClO4 electrolyte solution after Ppy depositions. 3. Results and discussion Fig. 1a and b are AFM images of Ppy thin ®lms polymerized in 0.1 M NaClO4 and in 0.1 M NaNO3 solution. These AFM images indicate that the surface of Ppy thin ®lm polymerized in NaClO4 is more swelled than that of NaNO3. This fact is consistent with the result of our previous report that Ppy ®lm swells when perchlorate anion is used as dopant by anion doping and solvent transfer into the ®lm [4,5,6]. Table 1 shows one of obvious evidences that when Ppy ®lm is polymerized, especially when perchlorate anion is used, permeation is relatively bigger than other anions. In case of NO3ÿ anion, the change of resonant frequency before and after dry is only about 3 kHz. But in case of NaClO4, the change is about 17 kHz. On these simple comparisons, the solvent effect is clearly observable during the deposition
0379-6779/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 ( 0 0 ) 0 0 5 5 5 - 5
138
S.-H. Song et al. / Synthetic Metals 117 (2001) 137±139
Fig. 2. Cyclic voltammetries of Ppy films polymerized in 0.1 M NaClO4 and 0.1 M NaNO3 solution and cycled in 0.1 M LiClO4 electrolyte solution; (a) potential Ð current, (b) potential Ð frequency shift. Fig. 1. AFM images of Ppy thin films (a) polymerized in NaClO4 and (b) polymerized in NaNO3 for 180 s image areas are 2 2 mm2.
Table 1 The change of resonant frequency and admittance intensity values of Ppy/anion film before and after dry Electrolyte
Wet condition
Dry condition
Mass change (ng)
NaNO3 NaClO4 LiClO4 KClO4
8828570 Hz, 4350 mV 8796950 Hz, 1210 mV 8797072 Hz, 1420 mV 8802990 Hz, 1178 mV
8831593 Hz, 4630 mV 8814054 Hz, 4846 mV 8815370 Hz, 4665 mV 8819420 Hz, 4440 mV
2748 15549 16634 14936
processes. The water in the Ppy ®lm is very important for using the ®lm as a capacitor. As shown in Fig. 2a, Ppy thin ®lm polymerized in NaNO3 is superior in the respect of conductivity from the differences of redox peak than that in NaClO4. But for capacitor characteristics, Ppy thin ®lm polymerized in NaClO4 shows more possibility than that in NaNO3. Fig. 2b shows that frequency shift of Ppy thin ®lm polymerized in NaClO4 recovers to the initial value after one cycle of potential sweep. But the case of NaNO3 indicates the intercalation of ions about 150 Hz in Ppy ®lm. These frequency characteristics also imply the fact that Ppy thin ®lm polymerized in NaClO4 has an ideal capacitor property during redox cycle.
Acknowledgements This work was supported by the academic research fund (KRF-2000-041-E00377) of Ministry of Education, Korea and Dong-A University.
References [1] C.T. Lee, J.H. Kim, B.W. Cho, Prospect. Ind. Chem. 2 (1999) 16. [2] D.S. Gottesfeld, S. Shin, X. Ren, J. Davey, in: The 8th International Seminar on Double Layer Capacitors and Similar Energy Storage Devices, Deerfield Beach, Florida, 7±9 December 1998.
S.-H. Song et al. / Synthetic Metals 117 (2001) 137±139 [3] K. Naoi, Y. Oura, M. Maaeda, S. Nakamura, J. Electrochem. Soc. 142 (1995) 417. [4] S.M. Chang, J.M. Kim, Y.K. Chang, Y.S. Kwon, H. Muramatsu, T. Ataka, Mol. Cryst. Liq. Cryst. 280 (1996) 157.
139
[5] J.M. Kim, H.W. Lee, Y.H. Kim, Y.S. Kwon, H. Muramatsu, S.M. Chang, Mol. Cryst. Liq. Cryst. 316 (1998) 141. [6] J.M. Kim, S.M.ChangH. Muramatsu, J. Electrochem. Soc. 146 (1999) 4544.