Electrodeposition and characterization of polypyrrole films on copper

In the present study, citric acid (CA), sodium acetate (SA) and sodium benzoate (SB) are used as electrolytes and compared in terms of easiness for polypyrrole deposition and film characteristics. Electrochemical measurements in the solution having these electrolytes with and without pyrrole demonstrate that copper can be efficiently passivated before PPy electrodeposition. This layer was sufficiently protective to inhibit further dissolution of the copper electrode and adequately conductive to enable the electropolymerization of pyrrole at the interface leading to the generation of an adherent polypyrrole film. The characterization of these coatings is carried out by cyclic voltammetry, UV–visible absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) studies. The performance of polypyrrole as protective coating against corrosion of Cu in both acidic and basic solutions is assessed by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS).     

High-response tri-layer electrochemical actuators based on conducting polymer films

Sandwich structured tri-layer films of polypyrrole/gold/polypyrrole have been electrochemically synthesized by successive oxidation of pyrrole in aqueous solutions and sputtering deposition of a thin gold layer, respectively. One of the polypyrrole layers was doped by a relatively large anion, dodecylbenzene sulfonate (PPy(DBS)) and the other one was doped by a smaller anion, benzenesulfonate (PPy(BS)). The tri-layer film could be deformed quickly by electrochemical reduction and oxidation of polypyrrole layers. The thin gold layer provided a highly conductive support for actuation. The tri-layered film could move from a position of 0° (vertical) to a position of +90° (oxidation) or ?90° (reduction) at potentials higher than 0.7 V or lower than ?0.7 V (vs. saturated calomel electrode (SCE)), respectively. The movement rate of the tri-layer film was ～260°/s at potentials of ±1.2 V vs. SCE, which was five times that of a PPy(DBS)/PPy(BS) bi-layer film. Furthermore, the tri-layer film could be driven at potentials as low as ±0.2 V vs. SCE. The bending motion rate of the tri-layer film increased quadratically with the increase of driving potential, while the motion rate of the bi-layer film, PPy(DBS)/PPy(BS), increased linearly with an increase of driving potential.     

Aniline electropolymerization on mild steel and zinc in a two-step process

A two-step process for aniline electropolymerization on mild steel and zinc from aqueous electrolytes has been developed. The first step is the electrodeposition of a thin polypyrrole film. It acts as a pretreatment of the surface and completely modifies its electrochemical response to usual acidic solutions suitable for aniline electropolymerization. It is much faster than any chemical pretreatment (less than 3 s) and can be performed with almost no metal dissolution. Pretreated mild steel or zinc substrates can then be used for the electrodeposition of a PANI film of controllable thickness. No or very little metal oxidation occurs in this second step. The films show stable electroactivity in acidic electrolytes, similar to that of PANI deposited on platinum, which indicates that the underlying oxidizable metal is fully protected. The overall system has a bilayer structure, indicating that the electrochemical interface during aniline electrodeposition might be situated at the polypyrrole ∣ solution interface. This suggests a new interpretation for the anticorrosion properties of conductive polymers based on the displacement of the electroactive interface from its usual location (metal ∣ solution) to the polymer ∣ solution interface.     

Electrocatalytic behavior of Pt-modified polyaniline electrode for methanol oxidation: Effect of Pt deposition modes

Platinum dispersed in polyaniline film is a better catalyst than bulk platinum for methanol electrooxidation in sulfuric acid solution. The effect of deposition modes of platinum particles on their electrocatalytic activity has been studied. Several electrodeposition methods, including constant potential, cyclic potential and double potential step, have been applied to characterize the performance of different electrodeposition modes. Besides the variation of the electrodeposition methods, rotating disk electrode technique is applied to disperse Pt particles under the control of convection–diffusion condition. The results show that the enhanced electrocatalytic activity may be due to the dispersion of Pt particles in the polyaniline film matrix and the synergistic effects between the dispersed Pt particles and the polyaniline film. Variables related to reaction kinetics, such as mass transport of species, concentration of methanol and acidity of solution, are investigated and reaction mechanism for methanol oxidation is discussed.     

Evaluation of the potential dependence of 2D–3D growth rates and structures of polypyrrole films in aqueous solutions of hexafluorates

Polypyrrole hexafluorosilicate, PPYSiF₆, and polypyrrole hexafluoroaluminate, PPYAlF₆, were found to follow the mixed 2DI–3DI kinetic model of electrodeposition in the potentials range (+0.80 V, +0.60 V) and (+0.95 V, +0.55 V) vs. SCE, respectively. The potentiostatic depositions of polypyrrole were performed on polycrystalline gold and on the single layer or bilayer polypyrrole films. Only in the case of the third layer deposition of PPYSiF₆ (on PPYSiF₆) at +0.6 V, the experimental current was found to fit better with the 2DP–3DI model. For electrodeposition of PPYAlF₆ on gold, a slightly better quality fitting with 2DP–3DP or 2DP–3DI kinetic models was observed only for some samples synthesized at 0.55 V. In general, contribution of the 2D structure in the polypyrrole deposits was observed to decrease with an increase of the polarization potential. Conclusions of the mathematical analysis of the current–time functions are in accordance with a texture of the outer surface of the polymer layers visible in SEM micrographs. The apparent rate constants of the lateral and outward growths of polypyrrole increase with potentials in (+0.55, +0.80) V range. Under assumption of the classical electrochemical kinetics law, the anodic transfer coefficients were found lower than 0.5. Values of the outward growth rate constant were of the order of 10⁻⁸–10⁻¹⁰ mol/(s cm²); being approximately one order of magnitude higher for polypyrrole hexafluorosilicate than for polypyrrole hexafluoroaluminate. The lateral growth rates of PPYAlF₆ on gold were found to depend on the electrodeposition potential more significantly than the outward growth rate. An increase in the growth rates with the potential was observed to diminish/vanish at E > +0.80 V, probably due to concurrent degradation processes of polypyrrole chains. The analysis of the deposition currents was done under conditions of the masking double layer currents that were characterized by the relaxation times of the order of seconds or longer.     

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.     

Electrochemical formation of Prussian blue films with a single ferricyanide solution on gold electrode

Experimental conditions for electrochemical deposition of Prussian blue (PB) from a single ferricyanide solution on the gold electrode surface are discussed. Various salts were used as supporting electrolyte in the PB electrochemical formation step and the experimental results show that only in the presence of KCl salt, the electrodeposition of PB can be obtained easily. Results also indicate that, with KCl as electrolyte, PB can be formed during potential cycling in a single ferricyanide solution only under rather extreme experimental parameters. Potential range is very effective in the formation of PB films. Successive cyclic voltammetry of ferricyanide solution in the small potential range (?0.1 to +0.6), only show the cyclic voltammogram of ferro/ferricyanide (i.e., electrodeposition of PB cannot be occur in this condition). Formation of PB is obtained in the extended positive potential range (?0.1 to +0.9). Gold electrode is the best suitable substrate as electrode in this electrodeposition condition. Also, the effect of pH, number of scan and concentration of ferricyanide in the electrochemical deposition of PB from a single ferricycanide solution were investigated and the optimum conditions were obtained.     

A new approach to metal electrodeposition at a periodically changing rate: Part I. The reversing overpotential method

A method of increasing the apparent deposition exchange current density value in reversing overpotential (RO) copper electrodeposition is described. In pulsating overpotential (PO) metal electrodeposition, the current density during the ‘off’ period is anodic, and proportional to the exchange current density value. The current during the ‘off’ period in PO copper electrodeposition can be increased by appropriate anodic polarization. This method is referred to as the RO method to distinguish it from the pulsating method. In order to maintain the average current density in this case, it is necessary to increase the cathodic current density during the ‘on’ period. Hence, the current density during the anodic period can be considered as proportional to the exchange current density for some other deposition process, characterized by a larger exchange current density value. The apparent deposition process exchange current density can be increased easily by using different current densities during the anodic period, and different morphologies for the same average current density can be expected. In this way, previously unknown morphologies of copper electrodeposits in the overpotential region used were obtained as spongy and needle-like forms.     

Optical characterization of bismuth reversible electrodeposition

Reversible electrodeposition of metallic bismuth onto transparent conducting substrates was studied with interest in the electrochromic phenomena produced by plating and stripping a thin metallic film. Different bismuth films were prepared potentiostatically by applying potential steps of different amplitude (whilst maintaining the electric charge at a constant value), and the change in transmittance was followed in situ simultaneously during the electrodeposition process. A large change of transmittance was observed for constant charge films prepared at different deposition potentials. As the absorbance is related to the deposition charge (amount of metallic bismuth electrodeposited), changes in optical properties of equivalent films must be related to large changes in film morphology; this was corroborated by scanning electron microscopy. The effect of copper additives was also analyzed: this produced changes in film morphology, leading to bidimensional deposition being predominant over the tridimensional process.     

Oxalic acid adsorption and oxidation at platinum single crystal electrodes

Oxalic acid adsorption and oxidation processes have been studied at platinum single crystal electrodes with basal orientations. Cyclic voltammetry and charge displacement experiments have been combined with in situ external reflection infrared experiments for the study of oxalic acid adsorption at potentials below 0.70 V. Whereas reversible anion-like adsorption is observed for Pt(100) and Pt(111) electrodes, oxalic acid is reduced at Pt(110) leading to the formation of an irreversibly bonded adsorbate which has been identified as adsorbed CO from the infrared spectra. Spectroscopic data confirm the potential dependent behaviour of oxalic acid adsorption on Pt(111) and Pt(100) electrodes derived from electrochemical data. At the same time, the infrared spectra show distinct C–O stretching bands for adsorbates on Pt(100) and P(111). In acidic solutions (pH = 1), for which oxalic acid and bioxalate anions predominate as solution species, oxalate anions are adsorbed at the Pt(100) electrode surface whereas bioxalate anions seem to be the adsorbed species at Pt(111). In neutral solutions, oxalate anions are adsorbed on both Pt(111) and Pt(100) surfaces. No intermediates coming from oxalic acid other than adsorbed CO for Pt(110) and adsorbed (bi)oxalate anions for Pt(111) and Pt(100) are detected during the oxidation of oxalic acid. Adsorbate bands are observed between 1400 and 1600 cm^?1 for the Pt(111) electrode for potentials between 0.85 and 1.0 V. These bands are related to adsorbed carbonate anions formed in the presence of carbon dioxide molecules generated from oxalic acid oxidation.     

Time-differential frequency response of electrochemical quartz crystal electrode during the dissolution and deposition processes of Au in H2SO4 solution containing chloride ion

Time-differentiation of the frequency response observed with electrochemical quartz crystal microbalance (EQCM) was applied for the analysis of the electrode processes for the Au electro-dissolution and deposition in acidic aqueous solution containing free chloride ion (Cl⁻). Evaluation for the values of the apparent equivalent molar mass per second proved the generation of the Au(I) species during the oxidation and reduction reactions of Au electrode in the presence of Cl⁻ at a level of 10 mM, which has not been reported so far. It was found that the electron-transfer reactions composed of Au(0), Au(I) and Au(III) species are participated in the overall Au electro-dissolution and deposition reactions in the applied potential range from −0.10 to 1.50 V (vs. Ag/AgCl).     

Electrodeposition of Al–Ni intermetallic compounds from aluminum chloride-N-(n-butyl)pyridinium chloride room temperature molten salt

Electrodeposition of aluminum–nickel intermetallic compounds (particularly Ni₃Al) has been carried out onto platinum and mild steel cathodes from a 2:1 (mole ratio) aluminum(III) chloride-N-(n-butyl)pyridinium chloride (BPC) molten bath saturated with nickel(II) chloride at room temperature. A single phase of Al–Ni alloy is difficult to obtain by controlled-potential and controlled-current methods; however, it can be obtained by pulse current plating. The electrodeposition of nickel from an AlCl₃–BPC–NiCl₂ (6.14:3.07:0.09 mole ratio) molten bath occurs via an instantaneous nucleation mechanism in the very initial stage of the crystal growth. The deposition reaction mechanisms of nickel in this molten bath are revealed by electrochemical analysis. The experimental Tafel slope of 42 mV dec^?1 and the calculated transfer coefficient $\text{α}\text{→}{}_{\mathrm{<mtext>c</mtext>}}$of 1.5 suggest that the rate determining step is a charge transfer reaction of an adsorbed bare monovalent cation to the metallic state. The effect of the cycle regime on the electrodeposition of Al–Ni alloys has been investigated. The current efficiency for the deposition of alloys is about 99%.     

Quantitative histochemistry of sex differences of periodic acid-schiff reaction in mouse submandibular gland

Sex differences and the effects of androgen on periodic acid-Schiff (PAS) positive substance in the submandibular gland of ICR strain mice were investigated with microspectrophotometry. The relative amount of PAS-positive groups per unit volume and per cell in the secretory tubule portion accorded with tubule-cell size which was larger in untreated male mice than in female or castrated male mice; PAS-positive groups increased following administration of testosterone propionate to female and castrated male mice.The relative amount of PAS-positive groups per unit volume in the acinar portion was larger in male mice and in the testosterone propionate-administered mice than in female or castrated male mice, though this difference was less pronounced than in the secretory tubules. However, no obvious difference was observed when the relative amount of PAS-positive groups per acinar cell was compared among these groups.The cause of the difference between the relative amount of PAS-positive groups per unit volume and per cell in the acinar portion may be attributed to the changes of cell size. The acinar cell size was smaller in untreated male mice and in the testosterone propionate administered mice than in female or in castrated male mice. It seems that androgen has little effect on the PAS-positive substance in the acinar cell, in contrast to its action on this substance in the secretory tubule cell.     

Electrodeposition of zinc+iron alloys: II. Relation between the stripping results and ex-situ characterization

Zn+Fe alloy electrodeposition under potentiostatic conditions was studied in chloride medium on vitreous carbon from solutions with relatively low metal concentrations. It has been demonstrated that electrochemical stripping techniques can be used to characterize the Zn+Fe alloy deposition process. Morphological and compositional studies, along with structural XRD analysis, enabled the electrodeposition conditions for obtaining a defined coating with defined characteristics to be specified. Anomalous codeposition of Zn+Fe alloy was maintained under gentle stirring conditions until zinc-rich deposits were obtained. In highly zinc-rich deposits, in which only the η-phase is present, a distorted platelet-like shape was seen. The zinc oxidation of these deposits took place in only one peak/plateau region in the electrochemical stripping curves. A slight increase in iron in the deposits (%Fe>4%) caused significant changes in both morphology and structure. For these deposits a second, more negative, peak/plateau region was recorded for the zinc oxidation in the stripping curves. Although the η-phase remains the phase mainly formed, the greater difficulty of zinc oxidation is interpreted as a consequence of the interactions between the η-phase and a new phase that probably has an fcc structure.     

Electrochemical behaviour of amino acids on Pt(h,k, l). A voltammetric and in situ FTIR study. Part II. Serine and alanine on Pt(111)

A spectroelectrochemical study of the adsorption and oxidation of serine and alanine on Pt(111) electrodes has been carried out in 0.1 M HClO₄ solutions. From the voltammetric and FTIR spectroscopic results, we concluded that adsorbed cyanide is formed at the Pt(111) surface as a product of serine and alanine oxidation. In the case of serine, adsorbed cyanide is detected at potentials above 0.4 V, whereas a higher potential is needed in the case of alanine. Linear and multibonded CO have also been detected as poisoning species during serine oxidation. These adsorbed species have been isolated by irreversible adsorption experiments of amino acids. Dissolved CO₂ has been found by FTIR spectroscopy as an oxidation product of both amino acids. The role played by the R group in the electrochemical behaviour of these molecules is significant. Reversibly adsorbed serinate and alaninate anions have been also detected. As in the case of the anions present in glycine solutions, the serinate and alaninate anions are two-fold coordinated to the Pt(111) surface through the car?ylate group.     

Dicyanomethylene derivatives of squaric acid: electrochemical behaviour and ESR investigation

The electrochemical behaviour of mono- and bisdicyanomethylene-substituted squaric acid dianion was investigated in dimethylformamide and acetonitrile on a Pt electrode. In cyclic voltammetry the oxidation of these dianions involves two successive, chemically reversible, one-electron processes, affording the corresponding radical anions and neutral species. The redox potentials are strongly dependent upon the number of dicyanomethylene substituents. Whereas the neutral species are stable only in the time scale of the voltammetric experiments, the radical anions can be accumulated by macroscale electrolysis. The ESR spectra of these radicals are reported. The monosubstituted dianion is protonated by electrochemical oxidation of hydrogen, whereas the disubstituted ones are not. Compounds obtained from the disubstituted dianions and the methyl viologen dication are also described.     

Nicotinic acid as brightener agent in copper electrodeposition

Copper electrodeposition on platinum electrodes from slightly acidic solutions of copper sulphate containing nicotinic acid (NA) is studied. The electrochemical results indicate that NA produces an inhibition of the copper deposition, probably related to the additive adsorption. Also, complex species formation between NA and cuprous ions occur at the interface. Nicotinic acid acts as a very effective brightener producing highly uniform and smooth surfaces of copper deposits. Surface morphology, brightness and adherence depend on the potential at which the deposition is performed.     

Electrochemical sensor for trace silicic acid detection based on bismuth film electrode

A highly sensitive voltammetric detection of silicic acid (SA), the main chemical species of dissolved silica in sea water, is described. The protocol relies on a fast square-wave voltammetric measurement of the decreased molybdenum stripping signal due to the formation of silicomolybdate complex. The cathodic stripping experiments were performed at the bismuth film electrode using HCl–KCl (pH 1.6) buffer solution. Different ligands, pH, ligand concentration, deposition potential and accumulation time were evaluated. Under the optimal conditions, a linear response is observed over the 50–400 μg L⁻¹ SA concentration range with a detection limit of 2 μg L⁻¹. A highly stable response, with a relative standard deviation (RSD) of 4.8%, is observed for 10 repetitive measurements. Such an electrochemical approach offers great promise for a simple, rapid, sensitive, and on-site or in situ real-time detection of SA.     

Study of the influence of the polyalcohol sorbitol on the electrodeposition of copper–zinc films from a non-cyanide bath

The electrodeposition of copper–zinc on to AISI 1010 steel from an alkaline non-cyanide solution containing sorbitol was investigated, with various proportions of the metal ions in the bath. Voltammetric curves indicated that the complexation of copper ion by sorbitol is beneficial, since the copper complex reduction potential is close to that of the zincate ion, implying that codeposition of copper and zinc should occur. EDS analysis showed that varying the ratio of copper to zinc ions in the plating bath affects the proportion of metals in the deposits, leading to golden or greyish bright films, even in the high-hydrogen-evolution potential region, indicating that sorbitate anions prevent the deposits becoming darker in this region. The narrow variation in film colour at various deposition potentials and charge densities showed that rigorous control of the alkaline-sorbitol plating bath and deposition conditions is not necessary. SEM analysis showed that the films were without stress and the substrate was fully covered. X-ray spectra suggested that a mixture of Cu₈0 and CuZn₂ alloy was deposited at ?1.14 V in all the baths studied while Cu_0.61Zn_0.39 (Cu-70 bath), Cu₅Zn₈ (Cu-50 bath) and CuZn₅(Cu-30 bath) films were deposited at both ?1.45 and ?1.60 V.     

Obtention and characterisation of cobalt+copper electrodeposits from a citrate bath

The electrodeposition of cobalt+copper alloy on vitreous carbon, copper and nickel electrodes in a citrate bath at pH ca. 5 has been studied for two [Co(II)]/[Cu(II)] ratios in solution. Voltammetric and stripping results on vitreous carbon show that co-deposition of the two metals takes place under these conditions. Electrodeposition leads to the formation of a solid solution of cobalt in copper, detected by only one oxidation peak that shifts from the copper to the cobalt position as the applied current density–applied potential is made more negative. Structural XRD analysis and compositional analyses, confirm the formation of a cobalt–copper solid solution of face-centred-cubic (fcc) structure. Diffractograms show peaks that appear at diffraction angles between the lines corresponding to copper and fcc cobalt. The value of the fcc lattice constant a of the alloy decreases linearly with the increase in the cobalt percentage in the deposits, following Vegard's law. Deposits obtained at the same charge and current density from the same bath on different substrates have similar morphology: nodular-grained deposits at low deposition current densities–applied potentials, which evolve gradually to more fine-grained and structured deposits as the cobalt percentage in the deposits is increased.