Galvanostatic Technique Research Articles

Morphological investigations of polypyrrole coatings on stainless steel

In this paper, electrochemical polymerization of pyrrole on 316L stainless steel substrates was accomplished using a rotating disc electrode (RDE). By applying various current densities and disc rotation speeds, coatings were produced with the aid of galvanostatic technique. Experiments were performed in an aqueous solution containing 0.2 M pyrrole and 0.1 M oxalic acid. Current densities and disc rotation speed ranges were from 0.05 to 1.0 mA/cm 2 and from 0 to 1500 rpm, respectively. Using a scanning electron microscope (SEM), the morphology of polypyrrole coatings was studied, and the morphology diagram was determined. The results obtained showed that various morphologies were obtained by changing the current density and/or disc rotation speed. These results also showed that apart from conventional morphologies of polypyrrole coatings reported in the literature, a new semicrystalline morphology was obtained under the conditions of very low current density (0.05 mA/cm 2) and disc rotation speed (≤50 rpm). The degree of crystallinity of this morphology was estimated to be 68% by grazing-incidence small-angle X-ray scattering (GISAXS). The elemental analysis (CHN) revealed the ratio of semicrystalline polypyrrole to oxalic acid dopant to be 4:1.

Nanocrystalline structure and nanopore formation in modified thermal TiO 2 films

The anodic TiO 2 films on Ti 0 substrates were synthesized using different electrochemical techniques including potential step, potentiodynamic, and galvanostatic technique, from a 1 M Na 2 SO 4 + 10 mM NaF solution. The AFM imaging of film surfaces revealed that thin films ( h < 20 nm ) are composed of small spherical-shaped nanocrystals, up to 20 nm in size. In thicker TiO 2 films ( h > 20 nm ) , cylindrical nanopores with diameter of ca. 30 nm, are formed. In contrast to the nanocrystalline nature of anodic TiO 2 films, thermally grown TiO 2 films at 850 °C are composed of oriented large pyramidal crystallites (200–500 nm in size), which are transformed into even larger moulds (2– 3 μ m in size) at 1050 °C. Thermal films of this type have been known to show inferior surface properties leading to large reflectance losses and the presence of surface states, which promote the electron–hole recombination. In this paper, we propose a new way to remedy these disadvantages of thermal films by special low temperature electrochemical anodic treatment. We have found that by the anodic treatment of thermally grown TiO 2 films, it is possible to control the surface properties, such as the nanocrystalline structure and nanopore formation. These features are desirable for solar energy conversion devices and solar hydrogen production, where the enhancement of electrocatalytic activity by increasing real surface area, reduction of reflectance losses, and removal of surface states created by thermal growth, are of primary importance. The tested electrochemical treatment included program waveforms inducing nanocrystallinity and nanopore formation. The pulse-voltammetric procedures are proposed to control surface non-stoichiometry of TiO 2 films and surface-states density of the photoelectrodes.

Conditions to prepare PPy/Al 2O 3/Al used as a solid-state capacitor from aqueous malic solutions

The electrosynthesis of polypyrrole (PPy) has been achieved on aluminium in aqueous medium of malic acid by means of cyclic voltammetry, potentiostatic and galvanostatic techniques. Scanning electron microscopy (SEM) and X-ray microanalysis by dispersion energy spectroscopy (EDS) applying on surfaces show that the PPy coating is developed from the metal surface through the cracks of the initial Al 2O 3 layer. Moreover, the results reveal that the homogeneity of the film achieved increases with the time of electropolymerization. A mechanism involving the participation of the supporting electrolyte and the pyrrole (Py) in distinct active sites was proposed based on the linear sweep voltammetry. It is observed for all the applied electrochemical techniques that the pyrrole concentration has to be higher than 0.1 M to allow the polypyrrole electrodeposition in acid medium. Scanning electron microscopy, secondary electrons (SE) and backscattering electrons (BE), shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. The corrosion results in 3% NaCl medium show that the PPy coating decreases the corrosion behaviour of the aluminium. The bilayer Al 2O 3/PPy shows a capacitor with future applications.

Potential oscillations during the electrochemical treatment of white liquor

Potential oscillations during the electrochemical treatment of white liquor are reported on. White liquor in the kraft process is composed mainly of sodium sulfide, sodium hydroxide, and sodium carbonate. Cyclic voltammetry, linear galvanic voltammetry, and galvanostatic techniques are used to characterize the behavior of the potential oscillations. The amplitude of the harmonic potential oscillations is between −150 and 750 mV (SCE). The behavior of the potential oscillations strongly depends on the applied current density, temperature, and mass transfer. Electrochemical impedance spectroscopy is employed to study the origin of the oscillations during the electrochemical treatment of the white liquor on the Ti/Ta2O5-IrO2 electrodes. Negative faradaic impedance is observed in the potential range of the potential oscillation amplitudes, and equivalent circuits are designed to fit the experimental impedance spectra. The potential oscillations are caused by the synergic effect of sulfur formation/removal and oxygen evolution in the high-potential range.

Electrodeposition of polypyrrole on aluminium in aqueous tartaric solution

The electrosynthesis of polypyrrole (PPy) has been achieved on aluminium in aqueous medium of tartaric acid by means of cyclic voltammetry, potentiostatic and galvanostatic techniques. Scanning electron microscopy (SEM) and X-ray microanalysis by energy spectroscopy dispersion (EDS) applying on surfaces show that the PPy coating is developed from the metal surface through the cracks of the initial Al 2O 3 layer. A mechanism involving the participation of the supporting electrolyte and the pyrrole (Py) in distinct active sites was proposed based on the linear sweep voltammetry. It is observed for all applied electrochemical techniques that the pyrrole concentration has to be higher than 0.1 M to allow the polypyrrole electrodeposition in acid medium. Scanning electron microscopy, secondary electrons (SE) and backscattering electrons (BE), shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. Moreover, EDS reveals a good homogeneity and compactness of the film achieved in galvanostatic method. The corrosion results in 3% NaCl medium show that the PPy coating decreases the corrosion behaviour of the aluminium. The bilayer Al 2O 3/PPy shows a capacitor with future applications.

Synthesis and Characterization of Nanowire-Based Anisotropic Conductors

We investigated the potential of commercially available porous templates to be used for the fabrication of functional anisotropic conductors. A galvanostatic deposition technique was used to fabricate arrays consisting of 200 nm diameter nanowires inside the pores of polycarbonate membranes. A tape lift-off procedure allowed the complete removal of any residual metal from both sides of the polymer membrane to form an anisotropic conductive film. The 10 microm thick film has roughly 3 x 10(8) nanowires per cm2, and it showed near zero electrical resistance perpendicular to the surface while appearing completely open to circuits between any points on the surface. The preparation of the film, characterization using SEM, AFM, and resistance measurements are presented. The 1D conductivity of these membranes may have many potential applications for microelectronic interconnects for packaging technologies.

Electrochemical behaviour of a tin electrode in tartaric acid solutions

The electrochemical behaviour of tin in tartaric acid solutions was investigated using potentiodynamic and galvanostatic techniques. The E/ I curves showed that the anodic behaviour of tin exhibits active/passive transition. In the active dissolution potential region, tin dissolves as Sn(II) species, which are subsequently oxidized to Sn(IV). The active dissolution of tin increases with increasing tartaric acid concentration, sweep rate and temperature. Passivation is due to formation of Sn(OH) 4 and/or SnO 2 film on the anode surface. The dissolution process is controlled by diffusion. The E/ t curves displayed that the time needed to active passive transition increases with increasing acid concentration and temperature but decreases with increasing imposing anodic current density.

Characterization of sol–gel-derived NiO x xerogels as supercapacitors

NiO x xerogels were formed by the sol–gel method followed by heat-treatment under ambient pressure. The structure and properties of these materials were characterized by using X-ray diffraction, XPS, TEM, TGA–DTA and N 2 (77 K) adsorption. Electrodes with the xerogels were activated by cyclic voltammetry (CV) and their capacitive performance was evaluated by CV and galvanostatic technique in 7 M KOH solutions. A maximum specific capacitance of 696 F g −1 was obtained by constant current discharge with a current density of 2.0 mA cm −2 for the NiO x xerogels heat-treated at 250 °C. The results of in situ XRD of the NiO x xerogels after the charge/discharge recycling test showed that the NiO x xerogels might exhibit faradaic pseudocapacitance by surface redox from Ni(OH) 2 to NiOOH. The high performance obtained indicates that these materials are promising electrode materials for supercapacitors.

Recycling of nickel from NiOOH/Ni(OH) 2 electrodes of spent Ni–Cd batteries

In this work, nickel from the positive electrode of Ni–Cd batteries was recycled by chemical precipitation and electrodeposition. The structure of the material recovered by chemical precipitation is affected by temperature. Alfa nickel hydroxide is stable at low temperature but becomes beta nickel hydroxide with increasing of the synthesis temperature. Electrodeposition was accomplished by using the galvanostatic technique. The chronopotentiometric plots presented a plateau potential in the initial stage of the deposit growth due to the reduction of ionic nickel. Charge density of the plateau potential and charge efficiency decreased with increase in current density. Charge efficiency around 81.0% was the largest for current densities between 5.0 mA cm −2 and 10.0 mA cm −2 for q = 9.0 C cm −2. As charge density increased to 90.0 C m −2, the electrodeposition efficiency decreased. In this case, there is a second plateau potential at which the evolution of hydrogen on the nickel electrode, the principal reaction, is quickly reached. Charge density affects not only the reaction kinetics, but also the deposit morphology. A decrease in microporosity is observed with the increase in charge density. The microporosity increases as the current density increases for the same charge density.

Performance improvements of alkaline batteries by studying the effects of different kinds of surfactant and different derivatives of benzene on the electrochemical properties of electrolytic zinc

Electrolytic zinc powders were prepared in 12 M KOH, 4 wt.% zinc oxide solutions in the presence of different kinds of surfactant and organic additives using the galvanostatic technique. Then the electrochemical behavior of zinc was investigated using the sweep voltametry technique. Zinc samples electrolyzed in the presence of cationic cetyl trimethyl ammonium bromide (Zn-CTAB), have maximum corrosion rate. Furthermore, scanning electron microscopy revealed the highest surface area. Zinc deposited with anionic surfactants, sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS), have high dendritic and secondary growth. More zinc ions electrolyzed on the cathode electrode in the presence of SDBS compared with SDS. We suppose the Benzene molecule in SDBS changes morphology, thus effects of the benzene molecule is investigated by utilizing several organic compounds during zinc electrodeposition. Naphthalene with 10 pi electrons at two fused rings decreases corrosion rate and needle growth of zinc deposited, compared to benzyl chloride which has 6 pi electrons. Enhanced delocalization of pi electrons by strongly activating group (–NH 2) in the aniline molecule increases the corrosion rate and dendrites compared with benzyl chloride, which has the weakly activating group (–CH 2Cl). The addition of chloro benzene with inactivating and electrodrawing group (–Cl) creates high surface area without any dendritic growth. The effects of electrolyte additives on the electrochemical capacity of AA-sized alkaline Zn-MnO 2 batteries are verified. The addition of Triton X-100 in anode gel resulted in maximum electrical capacity. Anionic (SDBS and SDS) additives gave higher electrical capacity than cationic (CTAB). Also, the reaction mechanism for zinc electrodeposition in alkaline electrolytes and its dependence upon the presence of organic additives are discussed in detail.

The Mechanism of Silver(I) Oxide to Silver(II) Oxide Formation on Polycrystalline Silver Electrodes in 8 M KOH Solution

The kinetics of silver(II) oxide formation on polycrystalline silver electrodes in 8 M KOH solution was investigated by cyclic voltammetry, potentiostatic and galvanostatic techniques, and by the morphology of the silver(II) oxide structures determined by scanning electron microscopy. Potentiostatic investigations revealed unambiguously that the silver(II) oxide formation proceeded via a nucleation and 3-D growth process. Microscopic examinations provided undoubted evidence that nucleation, 3-D growth, and Ostwald ripening processes are involved in the stage of silver(II) oxide formation. In addition, it was found that two types of silver(II) oxide morphologies might be formed by progressive and instantaneous nucleation process in the silver(I) oxide layer covering the silver substrate.

Electropolymerization of poly( N-methylaniline) on mild steel: Synthesis, characterization and corrosion protection

Poly( N-methylaniline) (PNMA) coatings on a steel disc electrode have been successfully electrodeposited from N-methylaniline (NMA) in aqueous oxalic acid solution using potentiodynamic, potentiostatic and galvanostatic techniques. For the potentiodynamic synthesis, formation of the PNMA coatings was found to be strongly dependent on the upper potential limits and scan rates. Smooth and strongly adherent PNMA coatings were obtained under potentiodynamic conditions during sequential scanning of the potential region between −0.5 and 1.0 V, at a scan rate of 10 mV s −1. The PNMA coatings were characterized by cyclic voltammetry, FT-IR and UV–Vis spectroscopy and SEM techniques. It was shown that NMA converts the iron(III) species to iron(II) chemically, causing a decrease in the current value corresponding to the electrochemical conversion (repassivation). The corrosion behavior of steels covered by polymer was investigated by anodic potentiodynamic polarization technique and the Tafel test. The corrosion resistance of the PNMA coated steel was found to be considerably higher and the corrosion rate was much slower than that of bare steel.

Electrochemical deposition of nickel and nickel–thallium composite oxides films from EDTA alkaline solutions

An anodic electrodeposition procedure of nickel hydroxide and oxyhydroxide species using an alkaline bath containing 5 mM Ni 2+ and 5 mM ethylenediaminotetraacetic acid as a ligand compound is described. The positive effect of thallium oxides and Tl + on the rate of nickel deposition was estimated. In the presence of thallium species, the electrodeposition process of nickel oxide species is located at lower positive potentials of about 100–150 mV. The XPS analysis of nickel–thallium composite films, revealed the presence of Tl 2O 3. Tl 2O, Ni(OH) 2 and NiOOH, with an average composition independent of the specific electrochemical deposition procedure (i.e., potentiostatic, potentiodynamic or galvanostatic techniques).

Bi&lt;Sub&gt;2&lt;/sub&gt;O3를 첨가한 8M KOH용액에서 다결정 Ag전극의 전기화학적 거동

[ <TEX>$Bi_2O_3$</TEX> ]를 첨가한 8M KOH용액에서 다결정 Ag전극의 전기화학적인 거동과 생성된 산화물들의 미세조직 변화를 분석하였다. <TEX>$Bi_2O_3$</TEX>를 첨가한 8M KOH용액에서 Ag 산화물뿐만 아니라 새로운 Ag-Bi-O화합물들이 생성되는 것을 알 수 있었다. Ag(I) 산화물 생성 전위 영역에서는 <TEX>$Ag_2O$</TEX> 이외에, Ag-Bi-O 화합물이 핵 생성과 3D성장 과정에 의해서 생성되고, Ag(II)산화물 생성 전위 영역에서는 AgO뿐만 아니라 새로운 Ag-Bi-O화합물들이 핵 생성과 3D성장 과정에 의해서 생성되었다. Ag(I) 산화물 생성 전위에서 두 가지 형상의 Ag(I) 산화물이 생성되는 것을 SEM 조직에 의해 관찰하였다. The electrochemical behaviors of polycrystalline silver electrodes in 8M KOH solutions containing <TEX>$Bi_2O_3$</TEX> were studied under various conditions by cyclic voltammetry, potentiostatic and galvanostatic techniques as well as the morphology of the silver oxide structures by SEM. It was found that three new compounds comprising silver, bismuth, and oxygen as well as <TEX>$Bi_2O_3,\;Ag_2O$</TEX> and AgO were formed during the electrochemical oxidation of silver. In addition, the potentiostatic current transients were characterized by the appearances of the first current peaks corresponding to the formation of silver oxides, and the second current peaks corresponding to the Ag-Bi-O compounds, indicating the presence of the nucleation and 3D growth mechanism, in the potential regions of <TEX>$Ag_2O$</TEX> and AgO, respectively. Microscopic examinations showed that two types of silver (I) oxide morphologies are formed in the potential region of <TEX>$Ag_2O$</TEX>.

定電流電解重合によるZn上へのポリ2-ビニルピリジン膜の形成

Poly(2-vinylpyridine) films were deposited on Zn substrate by electropolymerization using galvanostatic technique at 30°C in pH 5 aqueous solution containing methanol. Films were also formed by employing cyclic voltammetry and potentiostatic techniques; these were compared with those formed using galvanostatic electrolysis. The thickness of films formed by galvanostatic electrolysis increased in proportion to the amount of charge passed during electropolymerization but decreased with increasing current density because of increased hydrogen evolution. The FT-IR spectra and the color of the films suggested that the structure of poly(2-vinylpyridine) films changed from the non-branched to the branched chain type with the higher current densities. The anodic current density for Zn dissolution in 3%NaCl solution was significantly decreased by coating with poly(2-vinylpyridine) films. After electropolymerization at 50 A•m-2, the anodic reaction was most inhibited, showing excellent corrosion resistance. Although the electrochemical techniques employed for the film preparation had no influence on the thickness or the structure of films, the films formed by galvanostatic electrolysis contained the fewest cracks and gave the best corrosion resistance.

Formation of Poly(2-vinylpyridine) Films on Zn by Galvanostatic Electropolymerization

Poly(2vinylpyridine) films were deposited on Zn substrate by electropolymerization using a galvanostatic technique at 30 � Ci n pH 5 aqueous solution containing methanol. Films were also formed by employing cyclic voltammetry and potentiostatic techniques; these were compared with those formed using galvanostatic electrolysis. The thickness of films formed by galvanostatic electrolysis increased in proportion to the amount of charge passed during electropolymerization but decreased with increasing current density because of increased hydrogen evolution. The FT-IR spectra and the color of the films suggested that the structure of poly(2-vinylpyridine) films changed from the nonbranched to the branched chain type at higher current densities. The anodic current density for Zn dissolution in 3% NaCl solution was significantly decreased by coating with poly(2-vinylpyridine) films. After electropolymerization at 50 A m � 2 , the anodic reaction was most inhibited, showing excellent corrosion resistance. Although the electrochemical techniques employed had no influence on the thickness or the structure of films, the films formed by galvanostatic electrolysis contained the fewest cracks and gave the best corrosion resistance.

Mechanism of Silver(I) Oxide Formation on Polycrystalline Silver Electrodes in 8 M KOH Solution

The kinetics of silver(I) oxide formation on polycrystalline silver electrodes in 8 M KOH solution was investigated by cyclic voltammetry, potentiostatic and galvanostatic techniques as well as the morphology of the silver(I) oxide structures by scanning electron microscopy. Potentiostatic investigations revealed unambiguously that the silver(I) oxide may be nucleated in the second stage as well as in the third stage of silver(I) oxide formation. Cyclic voltammograms showed that the second peak current could be larger than the third peak current with repetitive cycling. Microscopic examinations provided undoubted evidence that electrodissolution, nucleation, three-dimensional (3D) growth, and Ostwald ripening processes are involved in the initial stage of silver(I) oxide formation. In addition, it was found that two types of silver(I) oxide morphologies were formed by progressive nucleation and instantaneous nucleation process. On the basis of the experimental results, a model of silver(I) oxide formation involving electrodissolution, progressive nucleation, instantaneous nucleation, and 3D growth processes is proposed. © 2004 The Electrochemical Society. All rights reserved.

Effect of concentration and temperature on electrochemical oscillations during sulfide oxidation on Ti/Ta 2O 5–IrO 2 electrodes

The impact of current density, concentration, and temperature on the potential oscillations observed during the anodic oxidation of sulfide on Ti/Ta 2O 5–IrO 2 oxide electrodes is investigated. Electrochemical methods including: cyclic voltammetry, linear voltammetry, linear galvanic voltammetry, galvanostatic technique and electrochemical impedance spectroscopy are used in this study. The observed potential oscillations are caused by the periodic formation/removal of sulfur from the electrode surface. Increasing current density has the effect of increasing the frequency of oscillations as well as increasing the onset potential. Both increasing concentration and temperature gave rise to significant increases in current density prior to the onset of potential oscillations. The activation energy for electrochemical oxidation of sulfide was estimated from the temperature studies. Lifetime experiments were also conducted and demonstrated that potential oscillations have a detrimental impact on the electrode lifetime.

Electrochemical relaxation study of polythiophene as conducting polymer (I)

The electro synthesis of polythiophene film from 2,2′-bithiophene monomer was investigated using different electrochemical techniques. The stability and electrical conductivity of the prepared film were studied. The most stable polythiophene film which also show slow relaxation (lowest relaxation time) was obtained using a galvanostatic technique in acetonitrile solvent with TBAPF 6 as supporting electrolyte at 5 °C. As the donor number of the solvent increases, the relaxation time decreases. The relaxation time is also sharply affected by temperature.

Electrochemical recovery of cadmium from spent Ni–Cd batteries

In this work, cadmium from spent Ni–Cd batteries is recycled. Ionic cadmium is recovery from acidic solution using a galvanostatic technique. Electrodeposition charge efficiency and deposit morphology depend on current density. Charge efficiency reaches up to 85.0% for a current density between 5.0 and 10.0 mA cm −2 and decreases with the increase in current density. Pore size decreases with the increase in current density.