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The stability of poly(o-phenylenediamine) as an electrode material
Synthetic Metals 128 (2002) 121±125
The stability of poly(o-phenylenediamine) as an electrode material R. Mazeikiene, A. Malinauskas* Institute of Chemistry, GosÏtauto Street 9, LT-2600 Vilnius, Lithuania Received 7 August 2001; accepted 13 August 2001
Abstract The kinetics of the electrochemical degradation of poly(o-phenylenediamine) (POPD), deposited on platinum electrode, has been investigated at controlled electrode potential in 0.5 M sulfuric acid solution. The degradation process follows the ®rst-order kinetics and depends on the electrode potential. Within the potential range investigated, 0.1 to 0.9 V, the degradation rate constants (k) were found to vary between approximately 1:5 10 5 and 4:4 10 5 s 1 , and a linear dependence of these constants on the degradation potential (E) has been found with the slope of k vs. E of ca. 2:9 10 5 s 1 V 1 . # 2002 Elsevier Science B.V. All rights reserved. Keywords: Poly(o-phenylenediamine); Polyaniline; Stability; Degradation
1. Introduction Among many conducting and electroactive polymers, poly(o-phenylenediamine) (POPD) is of great interest regarding its potential use in various ®elds of technology. POPD can be easily obtained as a thin layer of self-limiting thickness on different conducting substrates via anodic electropolymerization [1±3]. POPD layers have been well characterized by electrochemical [1±11], quartz crystal microbalance [4], radiotracer [5,6], STM [7], and different spectroscopic techniques [7,9±11]. Two interesting properties of POPD, different from those, characteristic for usual conducting polymers like polyaniline (PANI) or polypyrrole (PPy) make it promising for applications in electrochemical and bioelectrochemical sensors. One of these properties relate to an unusual dependence of the electric conductivity on the redox state of this polymer. As opposed to PANI or PPy, POPD shows the conductivity in its reduced state, whereas its oxidized state is insulating. This determines the electrochemical properties of POPD, since many electrode redox processes of solution species have been shown to take place within a relatively narrow potential window, corresponding to the reduced (conducting) form of this polymer [12,13]. Within this potential window, electrocatalytic oxidation of some species proceed, making it possible to use POPD coatings for sensor and biosensor applications [14], like e.g. the electrooxidation of coenzyme NADH [15]. * Corresponding author. Tel.: 37-2-729-350; fax: 37-2-617-018. E-mail address: [email protected] (A. Malinauskas).
Another useful property of POPD is its permselectivity. When deposited onto electrode, POPD permits the diffusion of small redox active species like hydrogen peroxide to the electrode surface, whereas many other species, greater in size, are retarded at the polymer/solution interface. This useful property of POPD has been widely exploited for the development of sensors and biosensors [16±20]. For many applications, the stability of POPD should be of primary interest. It is well known that when used in an electrochemical system, many of the known conducting polymers undergo electrochemical degradation, producing low-molecular weight decomposition products [21]. Also, it has been shown that the rate of electrochemical degradation depends greatly on the electrode potential applied, e.g. an increase of electrode potential by 0.7±1.0 V causes an increase of the degradation rate constant as high as two orders of magnitude, as it was observed for PANI [22,23] and poly(N-benzylaniline) [24]. The present work has been aimed to investigate the kinetics of the electrochemical degradation of POPD, deposited as a thin ®lm on platinum electrode. 2. Experimental o-Phenylenediamine (Merck) and poly(sodium 4-styrenesulfonate) (PSS) with an average Mw of 106 (Aldrich) were used as received. All solutions used contained 0.5 M sulfuric acid. PI-50-1 model potentiostat, arranged with an X±Y plotter, was used in experiments. Electrochemical experiments were
0379-6779/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 ( 0 1 ) 0 0 5 2 0 - 3
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R. Mazeikiene, A. Malinauskas / Synthetic Metals 128 (2002) 121±125
performed in a three electrode cell, containing platinum wire working electrode, 5 mm in length and 0.5 mm in diameter, platinum wire counter-electrode, and a saturated Ag/AgCl reference electrode. All potentials reported are referred to this reference electrode. In all potential cycling experiments, potential sweep rate of 100 mV/s was used. POPD layers were deposited onto the working electrode by potential cycling procedure within the scan limits of 0.2 to 0.9 V for 20 min, performed in a solution, containing 0.5 M sulfuric acid and 10 mM of o-phenylenediamine. PSS-doped POPD layers were obtained by using the same procedure, except that the feed solution contained additionally 10 mM of PSS, as calculated with respect to one monomer unit of the polymer. Studies on the stability of POPD-modi®ed electrodes were performed by keeping the electrode in a supporting electrolyte of 0.5 M sulfuric acid, not containing o-phenylenediamine, under controlled potential, ranging from 0.1 to 0.9 V. At de®nite time periods, cyclic voltammograms (CVs) of the electrode were recorded (2 cycles) within the potential scan limits of 0.2 to 0.9 V. The anodic peak current, obtained in the second cyclic potential scan, was taken into account and used in the calculations. 3. Results and discussion Fig. 1 (trace 1) shows CV for POPD-modi®ed platinum electrode. An anodic peak centered around 0 V and a corresponding cathodic peak at ca. 0.1 V with a pre-peak at 0.1 V observed could be ascribed to reversible redox processes taking place in the polymer ®lm well documented in the literature [1±11]. The integration of anodic current vs. potential sweep within the potential range 0.2 to 0.4 V yields an apparent charge density of 2.3 mC/cm2 for the
redox process of POPD ®lm. The variations of the preparation procedure like e.g. the duration of electropolymerization have little in¯uence on the charge density of the resulting polymer ®lm, since electropolymerization proceeds in a self-limiting manner. At a high anodic potential, where active polymerizable species are produced, the ®lm is electrically insulating and impermeable for monomer species; thus, a relatively thin layer of just formed polymer ®lm hinders electropolymerization to proceed. After the holding of POPD-modi®ed electrode at a de®nite potential for a de®nite time period, some changes in CVs proceed (trace 2 of Fig. 1). Both anodic and cathodic peaks of POPD show more complicated character and appear to consist of several overlapping peaks. Earlier, up to four types of redox active centers with some different electrochemical behavior were claimed for POPD, however, the corresponding redox processes occur within a narrow potential window [3,4,6,8]. Also, broad anodic and cathodic peaks or waves are observed centered at ca. 0.8 and 0.5 V, respectively (Fig. 1), corresponding probably to some lowmolecular weight freely diffusing degradation products of POPD like e.g. quinones. It is essential that both anodic and cathodic peaks of POPD diminish in height. Also, the decrease of apparent charge density of the polymer ®lm proceeds. Obviously, the only reason for this is the degradation or decomposition of POPD ®lm, leading to low-molecular weight decomposition products. The rate of this degradation depends on the electrode potential applied. Fig. 2 shows the time dependence of a relative current of anodic peak for POPD-modi®ed electrode held at different potentials. It is seen that anodic peak current diminishes in all cases investigated. However, the rate of POPD degradation depends on the potential applied, being greater for higher potential values. Similarly, PSS-doped POPD layers showed a closely related degradation kinetics (Fig. 3). The data shown in Figs. 2 and 3 can be easily transformed according to a single 2-parameter exponential decay equation: Irel ae
Fig. 1. CVs for POPD-modified platinum electrodes: (1) for freshly prepared electrode, and (2) for the same electrode, held at a controlled potential of 0.9 V for 180 min.
bt
(1)
where Irel is a relative anodic peak current, t the reaction time, and a and b are the empirical coefficients. It follows from Eq. (1) that in terms of chemical kinetics, the coef®cient b represents the ®rst-order degradation rate constant. Thus, ®rst-order rate constants (k) can be easily obtained by treating the kinetic data according to Eq. (1). The data thus obtained for sulfate-doped POPD are summarized in Table 1. Within the potential limits investigated, k values range between 1:57 10 5 and 4:37 10 5 s 1 , corresponding to the half-period of degradation ranging between 12.2 and 4.4 h. When plotted against electrode potential, a linear dependence of k on E was obtained both for sulfate-doped and PSS-doped POPD ®lms (Fig. 4). Fitting these dependences to a linear equation: k k0 aE
(2)
R. Mazeikiene, A. Malinauskas / Synthetic Metals 128 (2002) 121±125
123
Fig. 2. Kinetic curves for the relative current of anodic peak for sulfate-doped POPD-modified platinum electrodes held at different electrode potential values (as indicated).
where k is the degradation rate constant, k0 its value at zero potential, E the degradation potential, and a an empirical coefficient, one can obtain: 1. For sulfate-doped POPD: k0 1:69 0:14 10 and a 2:89 0:28 10 5 s 1 V 1 .
5
s 1,
2. For PSS-doped POPD: k0 1:76 0:27 10 and a 3:34 0:51 10 5 s 1 V 1 .
5
s 1,
The dependence obtained differ drastically from those obtained earlier for PANI. With the use of in situ UV±Vis spectroelectrochemistry, the slope of log k vs. E of 8.96 V 1
Fig. 3. Same as in Fig. 2, obtained for PSS-doped POPD-modified electrodes.
124
R. Mazeikiene, A. Malinauskas / Synthetic Metals 128 (2002) 121±125
Fig. 4. Dependence of POPD degradation rate constant on the electrode potential, obtained for both forms of the polymer (sulfate- and PSS-doped, as indicated). Inset: dependence of the ratio of degradation rate constants for PANI and POPD on electrode potential. Table 1 First-order degradation rate constants and degradation half-periods for POPD films Potential (V) 0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
k 10
5
s
1
1:57 0:15 1:85 0:31 1:49 0:25 2:35 0:37 2:63 0:51 2:58 0:44 3:20 0:33 3:53 0:54 3:93 0:69 4:37 0:66 3:87 0:48
t1/2 (h) 12.2 10.4 12.9 8.2 7.3 7.5 6.0 5.4 4.9 4.4 5.0
1.34 V 1 has been obtained for PANI-modi®ed platinum electrode within the region of relatively low electrode potential, from 0.3 to 0.6 V [23]. These values are similar to the corresponding value for POPD-®lmed electrode obtained in the present work. The inset of Fig. 4 shows the dependence of the ratio of degradation constants for PANI and POPD on the electrode potential. It is seen that at low electrode potentials, not exceeding 0.6 V, the degradation of both of these polymers proceed at a similar rate. At higher anodic potential, a steep increase of the ratio kPANI/ kPOPD is observed, showing much faster degradation of PANI as compared to POPD. References
has been obtained within the degradation potential limits of 0.85±1.10 V vs. RHE, i.e. 0.65±0.90 V vs. Ag/AgCl [22]. Earlier, we obtained, following the same operation manner as in the present work, a slope of log k vs. E of ca. 6.4 V 1 within the potential limits of 0.6±0.9 V vs. Ag/AgCl for PANI-modi®ed platinum electrode [23]. The data of the present work, when plotted as log k vs. E, yield a much lower slope of 0:47 0:05 V 1 for sulfate-doped POPD. Close similar values could be obtained also for PSS-doped POPD. This means a much lower sensitivity of POPD degradation to an increasing electrode potential, as compared to PANI, within the range of relatively high electrode potential. On the other hand, the slope of log k vs. E ranging from 0.44 to
[1] K. Chiba, T. Ohsaka, N. Oyama, J. Electroanal. Chem. 217 (1987) 239. [2] K. Chiba, T. Ohsaka, Y. Ohnuki, N. Oyama, J. Electroanal. Chem. 219 (1987) 117. [3] E.Yu. Pisarevskaya, M.D. Levi, Elektrokhimiya 30 (1994) 50. [4] K. Martinusz, E. Czirok, G. Inzelt, J. Electroanal. Chem. 379 (1994) 437. [5] K. Martinusz, G. Inzelt, G. Horanyi, J. Electroanal. Chem. 395 (1995) 293. [6] K. Martinusz, G. Inzelt, G. Horanyi, J. Electroanal. Chem. 404 (1996) 143. [7] K. Ogura, M. Kokura, J. Yano, H. Shiigi, Electrochim. Acta 40 (1995) 2707. [8] M.-A. Goyette, M. Leclerc, J. Electroanal. Chem. 382 (1995) 17. [9] L.-L. Wu, J. Luo, Z.-H. Lin, J. Electroanal. Chem. 417 (1996) 53. [10] L.-L. Wu, J. Luo, Z.-H. Lin, J. Electroanal. Chem. 440 (1997) 173. [11] A. Malinauskas, M. Bron, R. Holze, Synth. Met. 92 (1998) 127.
R. Mazeikiene, A. Malinauskas / Synthetic Metals 128 (2002) 121±125 [12] [13] [14] [15]
M.D. Levi, E.Yu. Pisarevskaya, Electrochim. Acta 37 (1992) 635. M.D. Levi, E.Yu. Pisarevskaya, Synth. Met. 55±57 (1993) 1377. A. Malinauskas, Synth. Met. 107 (1999) 75. M.J. Lobo, A.J. Miranda, J.M. Lopez-Fonseca, P. Tunon, Anal. Chim. Acta 325 (1996) 33. [16] C. Malitesta, F. Palmisano, L. Torsi, P.G. Zambonin, Anal. Chem. 62 (1990) 2735. [17] S.V. Sasso, R.J. Pierce, R. Wella, A.M. Yacynych, Anal. Chem. 62 (1990) 1111.
125
[18] F. Palmisano, P.G. Zambonin, Anal. Chem. 65 (1993) 2690. [19] F. Palmisano, A. Guerrieri, M. Quinto, P.G. Zambonin, Anal. Chem. 67 (1995) 1005. [20] R. Garjonyte, A. Malinauskas, Sens. Act. B 56 (1999) 85. [21] A.A. Pud, Synth. Met. 66 (1994) 1. [22] A. Malinauskas, R. Holze, J. Appl. Polym. Sci. 73 (1999) 287. [23] R. Mazeikiene, A. Malinauskas, Synth. Met. 123 (2001) 349. [24] A. Malinauskas, R. Holze, J. Solid State Electrochem. 3 (1999) 429.
The stability of poly(o-phenylenediamine) as an electrode material R. Mazeikiene, A. Malinauskas* Institute of Chemistry, GosÏtauto Street 9, LT-2600 Vilnius, Lithuania Received 7 August 2001; accepted 13 August 2001
Abstract The kinetics of the electrochemical degradation of poly(o-phenylenediamine) (POPD), deposited on platinum electrode, has been investigated at controlled electrode potential in 0.5 M sulfuric acid solution. The degradation process follows the ®rst-order kinetics and depends on the electrode potential. Within the potential range investigated, 0.1 to 0.9 V, the degradation rate constants (k) were found to vary between approximately 1:5 10 5 and 4:4 10 5 s 1 , and a linear dependence of these constants on the degradation potential (E) has been found with the slope of k vs. E of ca. 2:9 10 5 s 1 V 1 . # 2002 Elsevier Science B.V. All rights reserved. Keywords: Poly(o-phenylenediamine); Polyaniline; Stability; Degradation
1. Introduction Among many conducting and electroactive polymers, poly(o-phenylenediamine) (POPD) is of great interest regarding its potential use in various ®elds of technology. POPD can be easily obtained as a thin layer of self-limiting thickness on different conducting substrates via anodic electropolymerization [1±3]. POPD layers have been well characterized by electrochemical [1±11], quartz crystal microbalance [4], radiotracer [5,6], STM [7], and different spectroscopic techniques [7,9±11]. Two interesting properties of POPD, different from those, characteristic for usual conducting polymers like polyaniline (PANI) or polypyrrole (PPy) make it promising for applications in electrochemical and bioelectrochemical sensors. One of these properties relate to an unusual dependence of the electric conductivity on the redox state of this polymer. As opposed to PANI or PPy, POPD shows the conductivity in its reduced state, whereas its oxidized state is insulating. This determines the electrochemical properties of POPD, since many electrode redox processes of solution species have been shown to take place within a relatively narrow potential window, corresponding to the reduced (conducting) form of this polymer [12,13]. Within this potential window, electrocatalytic oxidation of some species proceed, making it possible to use POPD coatings for sensor and biosensor applications [14], like e.g. the electrooxidation of coenzyme NADH [15]. * Corresponding author. Tel.: 37-2-729-350; fax: 37-2-617-018. E-mail address: [email protected] (A. Malinauskas).
Another useful property of POPD is its permselectivity. When deposited onto electrode, POPD permits the diffusion of small redox active species like hydrogen peroxide to the electrode surface, whereas many other species, greater in size, are retarded at the polymer/solution interface. This useful property of POPD has been widely exploited for the development of sensors and biosensors [16±20]. For many applications, the stability of POPD should be of primary interest. It is well known that when used in an electrochemical system, many of the known conducting polymers undergo electrochemical degradation, producing low-molecular weight decomposition products [21]. Also, it has been shown that the rate of electrochemical degradation depends greatly on the electrode potential applied, e.g. an increase of electrode potential by 0.7±1.0 V causes an increase of the degradation rate constant as high as two orders of magnitude, as it was observed for PANI [22,23] and poly(N-benzylaniline) [24]. The present work has been aimed to investigate the kinetics of the electrochemical degradation of POPD, deposited as a thin ®lm on platinum electrode. 2. Experimental o-Phenylenediamine (Merck) and poly(sodium 4-styrenesulfonate) (PSS) with an average Mw of 106 (Aldrich) were used as received. All solutions used contained 0.5 M sulfuric acid. PI-50-1 model potentiostat, arranged with an X±Y plotter, was used in experiments. Electrochemical experiments were
0379-6779/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 ( 0 1 ) 0 0 5 2 0 - 3
122
R. Mazeikiene, A. Malinauskas / Synthetic Metals 128 (2002) 121±125
performed in a three electrode cell, containing platinum wire working electrode, 5 mm in length and 0.5 mm in diameter, platinum wire counter-electrode, and a saturated Ag/AgCl reference electrode. All potentials reported are referred to this reference electrode. In all potential cycling experiments, potential sweep rate of 100 mV/s was used. POPD layers were deposited onto the working electrode by potential cycling procedure within the scan limits of 0.2 to 0.9 V for 20 min, performed in a solution, containing 0.5 M sulfuric acid and 10 mM of o-phenylenediamine. PSS-doped POPD layers were obtained by using the same procedure, except that the feed solution contained additionally 10 mM of PSS, as calculated with respect to one monomer unit of the polymer. Studies on the stability of POPD-modi®ed electrodes were performed by keeping the electrode in a supporting electrolyte of 0.5 M sulfuric acid, not containing o-phenylenediamine, under controlled potential, ranging from 0.1 to 0.9 V. At de®nite time periods, cyclic voltammograms (CVs) of the electrode were recorded (2 cycles) within the potential scan limits of 0.2 to 0.9 V. The anodic peak current, obtained in the second cyclic potential scan, was taken into account and used in the calculations. 3. Results and discussion Fig. 1 (trace 1) shows CV for POPD-modi®ed platinum electrode. An anodic peak centered around 0 V and a corresponding cathodic peak at ca. 0.1 V with a pre-peak at 0.1 V observed could be ascribed to reversible redox processes taking place in the polymer ®lm well documented in the literature [1±11]. The integration of anodic current vs. potential sweep within the potential range 0.2 to 0.4 V yields an apparent charge density of 2.3 mC/cm2 for the
redox process of POPD ®lm. The variations of the preparation procedure like e.g. the duration of electropolymerization have little in¯uence on the charge density of the resulting polymer ®lm, since electropolymerization proceeds in a self-limiting manner. At a high anodic potential, where active polymerizable species are produced, the ®lm is electrically insulating and impermeable for monomer species; thus, a relatively thin layer of just formed polymer ®lm hinders electropolymerization to proceed. After the holding of POPD-modi®ed electrode at a de®nite potential for a de®nite time period, some changes in CVs proceed (trace 2 of Fig. 1). Both anodic and cathodic peaks of POPD show more complicated character and appear to consist of several overlapping peaks. Earlier, up to four types of redox active centers with some different electrochemical behavior were claimed for POPD, however, the corresponding redox processes occur within a narrow potential window [3,4,6,8]. Also, broad anodic and cathodic peaks or waves are observed centered at ca. 0.8 and 0.5 V, respectively (Fig. 1), corresponding probably to some lowmolecular weight freely diffusing degradation products of POPD like e.g. quinones. It is essential that both anodic and cathodic peaks of POPD diminish in height. Also, the decrease of apparent charge density of the polymer ®lm proceeds. Obviously, the only reason for this is the degradation or decomposition of POPD ®lm, leading to low-molecular weight decomposition products. The rate of this degradation depends on the electrode potential applied. Fig. 2 shows the time dependence of a relative current of anodic peak for POPD-modi®ed electrode held at different potentials. It is seen that anodic peak current diminishes in all cases investigated. However, the rate of POPD degradation depends on the potential applied, being greater for higher potential values. Similarly, PSS-doped POPD layers showed a closely related degradation kinetics (Fig. 3). The data shown in Figs. 2 and 3 can be easily transformed according to a single 2-parameter exponential decay equation: Irel ae
Fig. 1. CVs for POPD-modified platinum electrodes: (1) for freshly prepared electrode, and (2) for the same electrode, held at a controlled potential of 0.9 V for 180 min.
bt
(1)
where Irel is a relative anodic peak current, t the reaction time, and a and b are the empirical coefficients. It follows from Eq. (1) that in terms of chemical kinetics, the coef®cient b represents the ®rst-order degradation rate constant. Thus, ®rst-order rate constants (k) can be easily obtained by treating the kinetic data according to Eq. (1). The data thus obtained for sulfate-doped POPD are summarized in Table 1. Within the potential limits investigated, k values range between 1:57 10 5 and 4:37 10 5 s 1 , corresponding to the half-period of degradation ranging between 12.2 and 4.4 h. When plotted against electrode potential, a linear dependence of k on E was obtained both for sulfate-doped and PSS-doped POPD ®lms (Fig. 4). Fitting these dependences to a linear equation: k k0 aE
(2)
R. Mazeikiene, A. Malinauskas / Synthetic Metals 128 (2002) 121±125
123
Fig. 2. Kinetic curves for the relative current of anodic peak for sulfate-doped POPD-modified platinum electrodes held at different electrode potential values (as indicated).
where k is the degradation rate constant, k0 its value at zero potential, E the degradation potential, and a an empirical coefficient, one can obtain: 1. For sulfate-doped POPD: k0 1:69 0:14 10 and a 2:89 0:28 10 5 s 1 V 1 .
5
s 1,
2. For PSS-doped POPD: k0 1:76 0:27 10 and a 3:34 0:51 10 5 s 1 V 1 .
5
s 1,
The dependence obtained differ drastically from those obtained earlier for PANI. With the use of in situ UV±Vis spectroelectrochemistry, the slope of log k vs. E of 8.96 V 1
Fig. 3. Same as in Fig. 2, obtained for PSS-doped POPD-modified electrodes.
124
R. Mazeikiene, A. Malinauskas / Synthetic Metals 128 (2002) 121±125
Fig. 4. Dependence of POPD degradation rate constant on the electrode potential, obtained for both forms of the polymer (sulfate- and PSS-doped, as indicated). Inset: dependence of the ratio of degradation rate constants for PANI and POPD on electrode potential. Table 1 First-order degradation rate constants and degradation half-periods for POPD films Potential (V) 0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
k 10
5
s
1
1:57 0:15 1:85 0:31 1:49 0:25 2:35 0:37 2:63 0:51 2:58 0:44 3:20 0:33 3:53 0:54 3:93 0:69 4:37 0:66 3:87 0:48
t1/2 (h) 12.2 10.4 12.9 8.2 7.3 7.5 6.0 5.4 4.9 4.4 5.0
1.34 V 1 has been obtained for PANI-modi®ed platinum electrode within the region of relatively low electrode potential, from 0.3 to 0.6 V [23]. These values are similar to the corresponding value for POPD-®lmed electrode obtained in the present work. The inset of Fig. 4 shows the dependence of the ratio of degradation constants for PANI and POPD on the electrode potential. It is seen that at low electrode potentials, not exceeding 0.6 V, the degradation of both of these polymers proceed at a similar rate. At higher anodic potential, a steep increase of the ratio kPANI/ kPOPD is observed, showing much faster degradation of PANI as compared to POPD. References
has been obtained within the degradation potential limits of 0.85±1.10 V vs. RHE, i.e. 0.65±0.90 V vs. Ag/AgCl [22]. Earlier, we obtained, following the same operation manner as in the present work, a slope of log k vs. E of ca. 6.4 V 1 within the potential limits of 0.6±0.9 V vs. Ag/AgCl for PANI-modi®ed platinum electrode [23]. The data of the present work, when plotted as log k vs. E, yield a much lower slope of 0:47 0:05 V 1 for sulfate-doped POPD. Close similar values could be obtained also for PSS-doped POPD. This means a much lower sensitivity of POPD degradation to an increasing electrode potential, as compared to PANI, within the range of relatively high electrode potential. On the other hand, the slope of log k vs. E ranging from 0.44 to
[1] K. Chiba, T. Ohsaka, N. Oyama, J. Electroanal. Chem. 217 (1987) 239. [2] K. Chiba, T. Ohsaka, Y. Ohnuki, N. Oyama, J. Electroanal. Chem. 219 (1987) 117. [3] E.Yu. Pisarevskaya, M.D. Levi, Elektrokhimiya 30 (1994) 50. [4] K. Martinusz, E. Czirok, G. Inzelt, J. Electroanal. Chem. 379 (1994) 437. [5] K. Martinusz, G. Inzelt, G. Horanyi, J. Electroanal. Chem. 395 (1995) 293. [6] K. Martinusz, G. Inzelt, G. Horanyi, J. Electroanal. Chem. 404 (1996) 143. [7] K. Ogura, M. Kokura, J. Yano, H. Shiigi, Electrochim. Acta 40 (1995) 2707. [8] M.-A. Goyette, M. Leclerc, J. Electroanal. Chem. 382 (1995) 17. [9] L.-L. Wu, J. Luo, Z.-H. Lin, J. Electroanal. Chem. 417 (1996) 53. [10] L.-L. Wu, J. Luo, Z.-H. Lin, J. Electroanal. Chem. 440 (1997) 173. [11] A. Malinauskas, M. Bron, R. Holze, Synth. Met. 92 (1998) 127.
R. Mazeikiene, A. Malinauskas / Synthetic Metals 128 (2002) 121±125 [12] [13] [14] [15]
M.D. Levi, E.Yu. Pisarevskaya, Electrochim. Acta 37 (1992) 635. M.D. Levi, E.Yu. Pisarevskaya, Synth. Met. 55±57 (1993) 1377. A. Malinauskas, Synth. Met. 107 (1999) 75. M.J. Lobo, A.J. Miranda, J.M. Lopez-Fonseca, P. Tunon, Anal. Chim. Acta 325 (1996) 33. [16] C. Malitesta, F. Palmisano, L. Torsi, P.G. Zambonin, Anal. Chem. 62 (1990) 2735. [17] S.V. Sasso, R.J. Pierce, R. Wella, A.M. Yacynych, Anal. Chem. 62 (1990) 1111.
125
[18] F. Palmisano, P.G. Zambonin, Anal. Chem. 65 (1993) 2690. [19] F. Palmisano, A. Guerrieri, M. Quinto, P.G. Zambonin, Anal. Chem. 67 (1995) 1005. [20] R. Garjonyte, A. Malinauskas, Sens. Act. B 56 (1999) 85. [21] A.A. Pud, Synth. Met. 66 (1994) 1. [22] A. Malinauskas, R. Holze, J. Appl. Polym. Sci. 73 (1999) 287. [23] R. Mazeikiene, A. Malinauskas, Synth. Met. 123 (2001) 349. [24] A. Malinauskas, R. Holze, J. Solid State Electrochem. 3 (1999) 429.