Investigation of the electrochemical behavior of metallo-tetraazaporphyrin modified silver and pyrolytic graphite electrodes in aqueous nitrite solution

Five new complexes of the type [M(OBTTAP)] (where M = Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺; OBTTAP = 2,3,7,8,12,13,17,18-octakis(benzylthio)-5,10,15,20-tetraazaporphyrin(2?)) were used to prepare modified silver and pyrolytic graphite electrodes and their electrochemical behavior towards the reduction of aqueous nitrite solution was investigated in acidic, neutral and alkaline medium. Of these electrodes, [Co(OBTTAP)] and [Cu(OBTTAP)] modified electrodes showed affinity for ${\mathrm{NO}}_2^{-}$ ions and thereby exhibited significantly altered cathodic responses. The [Co(OBTTAP)]/Ag electrode in acidic, neutral and also in alkaline nitrite solutions, exhibited a new one electron irreversible reduction wave at E_p,c ～ ?0.2 V vs. Ag|AgCl. The [Cu(OBTTAP)]/Ag electrode in acidic and neutral nitrite solutions also behaved in a similar manner. However, in alkaline aqueous nitrite solution it showed two successive one electron reductions, the first reversible reduction at E_1/2 = ?0.26 V and the second irreversible reduction at E_p,c = ?0.73 V vs. Ag|AgCl. Controlled potential electrolysis of alkaline nitrite solutions using a [Cu(OBTTAP)]/Ag cathode led to isolation of a nitrosyl complex. The peak current, particularly with [Cu(OBTTAP)]/Ag microelectrode in alkaline medium, showed a linear response to $[{\mathrm{NO}}_2^{-}]$ and could be exploited in the electrochemical sensing and determination of ${\mathrm{NO}}_2^{-}$.     

Novel photocathodic characteristics of organic bilayer composed of a phthalocyanine and a perylene derivative in a water phase containing a redox molecule

An organic bilayer composed of metal-free phthalocyanine (H₂Pc, p-type semiconductor) and perylene derivative (PTCBI, n-type semiconductor) was found to involve novel characteristics of photoelectrode working in the water phase. When the photoelectrode characteristics were investigated when the PTCBI has contact with water containing the redox molecule (${\mathrm{Fe}}^{\mathrm{III}}(\mathrm{CN}{)}_6^{3-}$ (electron acceptor)), it was shown by voltammetry that the photocathodic current due to the ${\mathrm{Fe}}^{\mathrm{III}}(\mathrm{CN}{)}_6^{3-}$ reduction occurs at the present electrode, which is different from the ordinary characteristics at the n-type semiconductor/water interface of the Schttoky junction. Separate voltammetric studies showed that the photocathodic characteristics of the H₂Pc/PTCBI bilayer are consistent with those of the H₂Pc single layer, indicating that there are pin-holes in the PTCBI layer of the bilayer; that is, the H₂Pc has direct contact with ${\mathrm{Fe}}^{\mathrm{III}}(\mathrm{CN}{)}_6^{3-}$ dissolved in water. Thus, it is inferred that the photocathodic current occurs at the H₂Pc surface. However, the action spectrum for the photocathodic current indicated that a broad visible light absorption (400–750 nm) by only PTCBI can also induce photocurrent generation especially at wavelengths shorter than 500 nm where absorption of the H₂Pc is absent or relatively weak. This is supported by the previous knowledge that the PTCBI exciton alone can contribute to carrier generation through charge separation at the H₂Pc/PTCBI interface. This study showed the novel photocathodic characteristics at the organic solid/water interface coupled with electron conduction through the n-type semiconductor, in addition to the ordinary characteristics at the p-type semiconductor/water interface.     

Adsorption of uracil on bismuth single crystal planes

Uracil adsorption at Bi(h k l) has been studied using impedance spectroscopy method. The limiting adsorption potential shift, Gibbs energy of adsorption $-\mathrm{\Delta }{G}_{\mathrm{A}}^{°}$ and interaction constant values a in the Frumkin isotherm have been calculated and compared with the corresponding data for Hg [V. Brabec, S.D. Christian, G. Dryhust, J. Electroanal. Chem. 85 (1977) 389; V. Brabec, S.D. Christian, G. Dryhust, Biophys. Chem. 7 (1978) 253]. It was found that the values of $|-\mathrm{\Delta }{G}_{\mathrm{A}}^{°}|$ increase in the order $\mathrm{Hg}<\mathrm{Bi}(111)<\mathrm{Bi}(01\overline{1})$, but the values of a are higher for Bi(h k l) compared with Hg [V. Brabec, S.D. Christian, G. Dryhust, J. Electroanal. Chem. 85 (1977) 389; V. Brabec, S.D. Christian, G. Dryhust, Biophys. Chem. 7 (1978) 253]. The values of the limiting adsorption potential shift are comparable for the Hg and Bi(h k l) electrodes.     

On the parameters affecting the characteristics of the “wired” glucose oxidase anode

We recently described a redox polymer with an $\mathrm{Os}(N,N^{\prime }\text{-}\mathrm{dialkylated}\mathrm{biimidazole}{)}_3^{2+/3+}$ redox center with a redox potential of ?195 mV vs. Ag|AgCl, 800 mV reducing relative to its 2,2′-bipyridine analog. The tethering of the centers to a poly(4-vinylpyridine) backbone through a 13 atom long spacer arm, provided for an apparent electron diffusion coefficient as large as 5 × 8.10^?6 cm² s^?1. The glucose electro-oxidation catalyst formed by “wiring” glucose oxidase with this polymer allowed the electro-oxidation of glucose already at ?360 mV vs. Ag|AgCl at pH 7.2, near the reversible potential of glucose oxidase, at a current density of 1.3 mA cm^?2 in the presence of 32 mM glucose concentration. Here we consider the parameters affecting the characteristics of this anode, compare the characteristics with those of an anode made with a short-tethered “wire” and describe the optimization of the composition of the “wired” glucose oxidase.     

Kinetic studies of reduction of nitrate ions at Sn-modified Pt electrodes using a quartz crystal microbalance

An electrochemical quartz crystal microbalance (EQCM) was used to determine the surface coverage of adsorbed nitrate during the reduction of nitrate on Sn-modified Pt electrodes. The rate equation was derived as a function of the surface coverage of nitrate, the concentration of hydronium ion and the electrode potential for an electrode with a tin coverage of ca. 0.35, which showed the highest activity of the electrodes reported so far. N₂ (30%) and ${\mathrm{NH}}_4^{+}(62\%)$ were produced. From the Tafel slope at a constant surface coverage (?0.115 V decade^?1) and the reaction orders (1.1 and 0.94 with respect to the surface coverage of the adsorbed nitrate and the concentration of hydronium ion, respectively), it is concluded that the rate-determining step is the reaction of the adsorbed nitrate with the hydronium ion and an electron.     

The electroreduction of azides bound to nickel(II) ions in weak acidic media

Azide ions undergo reduction at the mercury electrode in slightly acidified media if they are coordinated to Ni(II) ions. Under such conditions, the electroreduction of Ni(II) to nickel amalgam is followed, at more negative potentials, by the parallel reduction of the ligand. The macro-scale electrolysis of slightly acidified solutions of $\mathrm{Ni}(\mathrm{II})''–''{\mathrm{N}}_3^{-}$ complexes showed the formation of ammonia and the evolution of bubbles of colorless gas. The electrode mechanism involves the direct electroreduction of ${\mathrm{N}}_3^{-}$ ions in the coordinated state according to the reaction scheme: ${\mathrm{N}}_3^{-}+4{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to {\mathrm{N}}_2+{\mathrm{NH}}_4^{+}$ as the suggested main reaction pathway, accompanied by a side reduction of ${\mathrm{N}}_3^{-}$ by nickel amalgam. In terms of this mechanism, the average coordination number of the reacting $\mathrm{Ni}(\mathrm{II})''–''{\mathrm{N}}_3^{-}$ complexes could be deduced. A molecular mechanism of the electroreduction of the azide ion bound to Ni(II) central ion was suggested.     

Preparation and characterization of ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate mixed films and their electrocatalytic properties

Polynuclear mixed-valent films of ruthenium oxide/hexacyanoferrate $(\mathrm{RuO}/\mathrm{Fe}(\mathrm{CN}{)}_6^{3-})$ and ruthenium hexacyanoferrate (RuHCF) have been prepared using repetitive cyclic voltammetry. The deposition process and the films’ electrocatalytic properties in electrolytes containing various cations have been investigated. The cyclic voltammograms recorded the deposition of the mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films directly from the mixing of Ru³⁺ and $\mathrm{Fe}(\mathrm{CN}{)}_6^{3-}$ ions from the acidic aqueous solutions containing various anions. The electrochemical quartz crystal microbalance, cyclic voltammetry, and UV–Vis spectroscopy were used to study the growth mechanism of the mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films. The mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films exhibited four redox couples with formal potentials that demonstrated a proton effect in acidic aqueous solution and an anion effect. The electrochemical quartz crystal microbalance results indicated that the redox process was confined to the immobilized mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate film. Electrocatalytic reactions of dopamine, epinephrine, norepinephrine, ${\mathrm{S}}_2{\mathrm{O}}_8^{2-}$, and ${\mathrm{SO}}_5^{2-}$ were carried out by the mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films. The electrocatalytic oxidation of ethyl alcohol, isopropyl alcohol, l-cysteine, and ascorbic acid by the mixed ruthenium oxide/hexacyanoferrate and ruthenium hexacyanoferrate films too was investigated.     

Characterization of iron hexachloroplatinate films and their electrocatalytic properties with NAD+, hemoglobin and O2

Iron hexachloroplatinate (FePtCl₆) films have been prepared by mixing Fe²⁺ and ${\mathrm{PtCl}}_6^{2-}$ ions in an aqueous KBr solution. The electrochemical quartz crystal microbalance (EQCM), rotating ring-disk electrode, UV–visible absorption spectroscopy, stopped-flow kinetic method and cyclic voltammetry were used to study the deposition and growth mechanism of the iron hexachloroplatinate films. The electrochemical and EQCM properties of the films indicated that a single redox process was confined to the immobilized iron hexachloroplatinate films. The deposition of an iron hexabromoplatinate film occurred when ${\mathrm{Pt}}^{\mathrm{IV}}{\mathrm{Cl}}_6^{2-}$ was electrochemically reduced to ${\mathrm{Pt}}^{\mathrm{II}}{\mathrm{Cl}}_6^{4-}$ and Fe³⁺ to Fe²⁺. In the aqueous KCl, pH 3.0, solution, ${\mathrm{Pt}}^{\mathrm{IV}}{\mathrm{Cl}}_6^{2-}$ was electrochemically reduced to ${\mathrm{Pt}}^{\mathrm{II}}{\mathrm{Cl}}_6^{4-}$ and the Fe²⁺ reacted with the ${\mathrm{Pt}}^{\mathrm{II}}{\mathrm{Cl}}_6^{4-}$ and ${\mathrm{Pt}}^{\mathrm{IV}}{\mathrm{Cl}}_6^{2-}$ species. The electrocatalytic reduction properties of NAD⁺ and hemoglobin were determined using the iron hexachloroplatinate films. The electrocatalytic and electrochemical reactions of NAD⁺ with an iron hexabromoplatinate film were investigated using the rotating ring-disk electrode method. The catalytic current increased with the increase of analyte concentration with slope of 1.6 μA/mM.     

The complex formation of ions with a phospholipid monolayer adsorbed at an aqueous|1,2-dichloroethane interface

The complex formation of phosphatidylcholine adsorbed at a water|1,2-dichloroethane, W|DCE, interface with ions was evaluated based on the desorption behavior of lipids at the interface accompanied by an ion transfer and was confirmed by measuring voltammograms for the ion transfer facilitated by the complex formation with lipids. The desorption behavior of lipids was measured according to the Wilhelmy vertical plate method, the cell of which was improved to achieve polarization of the W|DCE interface. Voltammograms for the ion transfer at the W|DCE interface facilitated by the complex formation with lipids were recorded at a micro W|DCE interface in order to avoid the influence of convection caused by the desorption of lipids at the interface. Lipids adsorbed at the W|DCE interface showed complex formation with alkali metal ions, ${\mathrm{NH}}_4^{+}\text{,}({\mathrm{CH}}_3){\mathrm{NH}}_3^{+}\text{,}({\mathrm{CH}}_3{)}_2{\mathrm{NH}}_2^{+}\mathrm{or}({\mathrm{CH}}_3{)}_3{\mathrm{NH}}^{+}$, but not with $({\mathrm{CH}}_3{)}_4{\mathrm{N}}^{+}$ or anions such as ${\mathrm{SO}}_4^{2-}$, CH₃COO^?, Cl^?, Br^?, ${\mathrm{NO}}_3^{-}$, I^? or ${\mathrm{ClO}}_4^{-}$. Lipids also showed strong complex formation with a basic amino acid such as an arginine cation, which has two amino groups in the molecule. The strength of the complex formation with lipids was ${\mathrm{Arg}}^{+}>{\mathrm{Li}}^{+}\text{,}{\mathrm{Na}}^{+}>{\mathrm{K}}^{+}>{\mathrm{NH}}_4^{+}>{\mathrm{CH}}_3{\mathrm{NH}}_3^{+}>({\mathrm{CH}}_3{)}_2{\mathrm{NH}}_2^{+}>{\mathrm{Cs}}^{+}>({\mathrm{CH}}_3{)}_3{\mathrm{NH}}^{+}$.     

Scanning electrochemical microscopy (SECM) study of superoxide generation and its reactivity with 1,4-dihydropyridines

A scanning electrochemical microscope (SECM), in the tip generation substrate collection and feedback modes, was used in a method to characterize the electrode mechanism of the ${\mathrm{O}}_2/{\mathrm{O}}_2^{\text{<mglyph src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ couple in dimethylsulphoxide (DMSO) containing 0.1 M tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte. Also the quantification of the interaction between ${\mathrm{O}}_2^{\text{<mglyph src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ and different 1,4-dihydropyridine compounds is reported.The SECM results demonstrated that the ${\mathrm{O}}_2/{\mathrm{O}}_2^{\text{<mglyph src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ couple follows an E mechanism, in contrast with the EC₂ mechanism (DISP 2) that was previously reported by cyclic voltammetry. This result implies that in the time scale of SECM measurements there is no time for a homogeneous chemical reaction to be coupled to the electron transfer, i.e., the superoxide is a stable radical. Also we have determined the heterogeneous standard rate constant, k⁰ of the quasi-reversible reduction of oxygen to superoxide anion.Taking advantage of the fact that the superoxide suffers no chemical decay during the SECM experiment, a method to obtain the direct interaction of different 1,4-dihydropyridine molecules with superoxide was developed. The study revealed that all the 1,4-DHPs scavenged superoxide with sufficiently high interaction constants (～10⁵ M^?1 s^?1). No significant difference between the different molecules was found.This paper shows that the SECM feedback mode is a sensitive technique, giving an accurate determination of the homogeneous interaction constant and allowing the determination of faster rate constants than those found from cyclic voltammetry.     

The electrochemical behaviour of the Pr(III)/Pr redox system at Bi and Cd liquid electrodes in molten eutectic LiCl–KCl

The electrode reactions of LiCl–KCl–PrCl₃ solutions at the surface of liquid electrodes, i.e. Cd and Bi, were investigated by electrochemical techniques. The redox potential of the Pr(III)/Pr couple at the liquid electrodes were observed at more positive potential values than those at one inert electrode. This potential shift was thermodynamically analysed by a lowering of activity of Pr in the metal phase. Cyclic voltammetry, using Cd and Bi pools as working electrodes, was conducted in order to study the reaction mechanism. The results suggest a quasi-reversible behaviour of the Pr(III)/Pr electrochemical system at the liquid electrodes, and the values of the kinetic parameters, k⁰ and α as well as the reversible half wave potential, $E_{1/2}^{\mathrm{r}}$, have been obtained. The interdiffusion coefficients of Pr in the metal phases seem to be similar to the diffusion coefficient of Pr(III) in solution. From comparison between the equilibrium potential adopted by a praseodymium electrode immersed in a solution containing Pr(III) ions, and the calculated $E_{1/2}^{\mathrm{r}}$ of the system Pr(III)/Pr–M (being M = Cd or Bi) it has been possible to estimate the activity coefficients of Pr in the Cd and Bi phases. Open circuit chronopotentiometry using Cd or Bi film electrodes was also conducted. Electromotive force, emf, measurements for various intermetallic compounds in two-phase coexisting states were carried out in the temperature range of 673–823 K. The activities and relative partial molar Gibbs energies of Pr were obtained from the measured emf for various Pr–Cd and Pr–Bi intermetallic compounds, PrCd₁₁, PrCd₆, PrCd_4.46, PrBi₂ and PrBi. The relative partial molar entropies and enthalpies of Pr were also calculated from the temperature dependence of the emf. The standard Gibbs energies of formation for the Pr–Cd and Pr–Bi intermetallic compounds were calculated.     

Microwave enhanced electrochemistry: mass transport effects and steady state voltammetry in the sub-millisecond time domain

In situ microwave activation of electrochemical processes is possible by self-focusing of intense microwave radiation into a region close to the electrode|solution (electrolyte) interface of a microelectrode placed inside a microwave cavity. A systematic study of the microwave activation effects in electrochemical processes is reported for two redox systems, $\mathrm{Fe}(\mathrm{CN}{)}_6^{3-/4-}\mathrm{and}\mathrm{Ru}({\mathrm{NH}}_3{)}_6^{3+/2+}$, in aqueous KCl solution. Platinum microelectrodes of 100, 50, and 25 μm diameter are employed and at the 25 μm diameter electrode, extreme current enhancements of up to three orders of magnitude are detected. A typical Nernst diffusion layer thickness in aqueous solution of less than 100 nm can be achieved routinely and, consequently, high temperature steady state voltammetry is possible in the sub-millisecond time domain. Volatile reagents reduce the efficiency of this effect and therefore a steam bubble mechanism is proposed to explain the observations. Microwave effects on the rate of interfacial electron transfer are discussed.     

Effect of niobium on the electronic properties of passive films on zirconium alloys

The effects of niobium on the structure and electronic properties of passive films formed on zirconium alloys in pH 8.5 buffer solution were examined by photo-electrochemical analysis. For Zr–xNb alloys (x = 0, 0.45, 1.5, 2.5 wt%), the photocurrent began to increase at an incident energy of 3.5–3.7 eV and exhibited the first peak at 4.3 eV and the second peak at 5.7 eV. From the (I_ph hν)^1/2 vs. hν plot, indirect band gap energies of $E_{\mathrm{g}}^1=3.01''–''3.47\mathrm{eV}\mathrm{and}{E}_{\mathrm{g}}^2=4.44''–''4.91\mathrm{eV}$ were obtained. With increasing Nb content, the relative photocurrent intensity of the first peak increased significantly. Compared with the photocurrent spectrum of the thermal oxide of Zr–2.5Nb, it was revealed that the first peak in the photocurrent spectrum for the passive film formed on Zr–Nb alloy was generated by two types of electron transitions; one caused by hydrous ZrO₂ and the other created by Nb. Two electron transition sources were overlapped over the same range of incident photon energy. In the photocurrent spectrum for passive film formed on Zr–2.5Nb alloy in which Nb is dissolved into the matrix by quenching, the relative photocurrent intensity of the first peak increased, implying that dissolved Nb acts as another electron transition source.     

The adsorption of thiourea on the mercury from neutral and acidic solutions of perchlorates

The adsorption of thiourea at the interface the mercury/1 mol dm^?3 NaClO₄ and the mercury/1 mol dm^?3 HClO₄ was studied in the function of the electrode potential and the adsorbate concentration. In the study was used, the experimental data obtained from the measurement of differential capacity of double layer, the measurement of zero charge potential, and surface tension at the zero charge potential. The information concerning thiourea adsorption was obtained from values of relative surface excess, free adsorption energy, interactions constants and the electrostatic parameters of the inner layer. It was found out that protonized thiourea molecules from HClO₄ solutions adsorb better at the interface the mercury/${\mathrm{ClO}}_4^{-}$. They are also characterized by stronger intermolecular interactions in comparison with thiourea molecules from NaClO₄ solutions adsorbing on the mercury.     

Current oscillatory phenomena based on electrogenerated superoxide ion at the HMDE in dimethylsulfoxide

A study on the current oscillation based on the electrogenerated superoxide ion $({\mathrm{O}}_2^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-})$ at a hanging mercury drop electrode (HMDE) in dimethylsulfoxide solution containing tetra-n-alkylammonium perchlorate as the electrolyte was carried out. Cyclic voltammetric, potential step chronoamperometric, normal and reverse pulse voltammetric techniques were employed in this study. A bare glassy carbon electrode, a liquid hemispherical mercury (Hg) drop-coated gold (Au) electrode and a Hg film-coated Au electrode were also used as working electrodes to understand the mechanism of the current oscillation. The experimental conditions were optimized for a simple, regular and reproducible current oscillation. The specific adsorption phenomenon of iodide ion and the adsorption of the alkyl chain of the supporting electrolyte on the HMDE surface were also considered to clarify the experimental factors governing the current oscillation phenomenon. It has been concluded that the oscillation is mainly due to the promoted oxidation (dissolution) of the HMDE itself by the adsorption of ${\mathrm{O}}_2^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$, resulting in the formation–destruction of a passive film such as ${\mathrm{Hg}}_2({\mathrm{O}}_2^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}{)}_2$ on the electrode surface. A probable mechanism for the observed current oscillation is discussed.     

The electrochemical self-assembly of the FAD modified zinc oxide films and their electrocatalytic properties

The flavin adenine dinucleotide (FAD) modified zinc oxide films have been prepared using repeated cyclic voltammetry to investigate both the deposition process and the films’ electrocatalytic properties. This paper describes the successful loading of electrochemically active molecules into ZnO by electrochemical method. The cyclic voltammograms recorded the direct deposition of the FAD/zinc oxide films over different scanning potential ranges from the mixed aqueous Zn²⁺ ions and FAD. In addition to the cyclic voltammetry, an electrochemical quartz crystal microbalance, UV–visible absorption spectroscopy, and the stopped-flow method were used to study the growth mechanism and their properties of the FAD/zinc oxide films. The results showed that the Zn²⁺ ions and FAD reacted by an electrochemical process to form a self-assembly FAD modified zinc oxide film. The FAD/zinc oxide films exhibited a single redox couple that included both the electron and proton transfer, with a formal potential that demonstrated a proton effect in acidic and basic solutions. The electrocatalytic reduction of NAD⁺ employing the FAD/zinc oxide films was investigated by cyclic voltammetry and UV–visible absorption spectroscopy methods. The electrocatalytic reduction of ${\mathrm{S}}_4{\mathrm{O}}_6^{2-}$, ${\mathrm{SO}}_5^{2-}\text{,}{\mathrm{S}}_2{\mathrm{O}}_8^{2-}\text{,}{\mathrm{ClO}}_3^{-}\text{,}{\mathrm{BrO}}_3^{-}\text{,}\mathrm{and}{\mathrm{IO}}_3^{-}$ ions using a FAD/zinc oxide film occurred in neutral aqueous solutions.     

Electrochemical behavior of Ni particles modified polypyrrole films studied by EQCN technique

Polypyrrole films modified with Ni Particles were eletrodeposited using a constant potential on a Pt/quartz crystal electrode with the aim to investigate the changes in the voltammetric and mass profiles compared with pure polypyrrole. The electrochemical behavior of the polypyrrole with Ni showed a new cathodic peak at ?0.73 V associated to Ni²⁺ reduction. Besides, it was characterized that there is a redox-pair of the polymer and Ni and a model was proposed to explain the phenomenon considering the eletroneutrality principle. The transport of the ${\mathrm{ClO}}_4^{-}$ ion into (or outside) the polymer is opposite to the expected direction. This occurs due to the redox-pair between the PPy chain and Ni species which can be explained by a loss of anions during Ni oxidation and the gain of anions during the Ni reduction.