Electrochimica Acta

Published by Elsevier
Online ISSN: 0013-4686
Publications
Article
It is well established that the structural details of electrodes and their interaction with adsorbed enzyme influences the interfacial electron transfer rate. However, for nanostructured electrodes, it is likely that the structure also impacts on substrate flux near the adsorbed enzymes and thus catalytic activity. Furthermore, for enzymes converting macro-molecular substrates it is possible that the enzyme orientation determines the nature of interactions between the adsorbed enzyme and substrate and therefore catalytic rates. In essence the electrode may impede substrate access to the active site of the enzyme. We have tested these possibilities through studies of the catalytic performance of two enzymes adsorbed on topologically distinct electrode materials. Escherichia coli NrfA, a nitrite reductase, was adsorbed on mesoporous, nanocrystalline SnO2 electrodes. CymA from Shewanella oneidensis MR-1 reduces menaquinone-7 within 200 nm sized liposomes and this reaction was studied with the enzyme adsorbed on SAM modified ultra-flat gold electrodes.
 
Article
Different approaches to enhancement of electrocatalytic activity of noble metal nanoparticles during oxidation of small organic molecules (namely potential fuels for low-temperature fuel cells such as methanol, ethanol and formic acid) are described. A physical approach to the increase of activity of catalytic nanoparticles (e.g. platinum or palladium) involves nanostructuring to obtain highly dispersed systems of high surface area. Recently, the feasibility of enhancing activity of noble metal systems through the formation of bimetallic (e.g. PtRu, PtSn, and PdAu) or even more complex (e.g. PtRuW, PtRuSn) alloys has been demonstrated. In addition to possible changes in the electronic properties of alloys, specific interactions between metals as well as chemical reactivity of the added components have been postulated. We address and emphasize here the possibility of utilization of noble metal and alloyed nanoparticles supported on robust but reactive high surface area metal oxides (e.g. WO3, MoO3, TiO2, ZrO2, V2O5, and CeO2) in oxidative electrocatalysis. This paper concerns the way in which certain inorganic oxides and oxo species can act effectively as supports for noble metal nanoparticles or their alloys during electrocatalytic oxidation of hydrogen and representative organic fuels. Among important issues are possible changes in the morphology and dispersion, as well as specific interactions leading to the improved chemisorptive and catalytic properties in addition to the feasibility of long time operation of the discussed systems.
 
Article
Nanoporous anodic aluminum oxide (AAO) has been explored for various applications due to its regular cell arrangement and relatively easy fabrication processes. However, conventional two-step anodization based on self-organization only allows the fabrication of a few discrete cell sizes and formation of small domains of hexagonally packed pores. Recent efforts to pre-pattern aluminum followed with anodization significantly improve the regularity and available pore geometries in AAO, while systematic study of the anodization condition, especially the impact of acid composition on pore formation guided by nanoindentation is still lacking. In this work, we pre-patterned aluminium thin films using ordered monolayers of silica beads and formed porous AAO in a single-step anodization in phosphoric acid. Controllable cell sizes ranging from 280 nm to 760 nm were obtained, matching the diameters of the silica nanobead molds used. This range of cell size is significantly greater than what has been reported for AAO formed in phosphoric acid in the literature. In addition, the relationships between the acid concentration, cell size, pore size, anodization voltage and film growth rate were studied quantitatively. The results are consistent with the theory of oxide formation through an electrochemical reaction. Not only does this study provide useful operational conditions of nanoindentation induced anodization in phosphoric acid, it also generates significant information for fundamental understanding of AAO formation.
 
Article
The potential for chemical reduction of hexavalent chromium Cr(VI) in contaminated water and formation of a stable precipitate by Zero Valent Iron (ZVI) anode electrolysis is evaluated in separated electrodes system. Oxidation of iron electrodes produces ferrous ions causing the development of a reducing environment in the anolyte, chemical reduction of Cr(VI) to Cr(III) and formation of stable iron-chromium precipitates. Cr(VI) transformation rates are dependent on the applied electric current density. Increasing the electric current increases the transformation rates; however, the process is more efficient under lower volumetric current density (for example 1.5 mA L(-1) in this study). The transformation follows a zero order rate that is dependent on the electric current density. Cr(VI) transformation occurs in the anolyte when the electrodes are separated as well as when the electrolytes (anolyte/catholyte) are mixed, as used in electrocoagulation. The study shows that the transformation occurs in the anolyte as a result of ferrous ion formation and the product is a stable Fe(15)Cr(5)(OH)(60) precipitate.
 
Article
Electroreductive desorption of a highly ordered self-assembled monolayer (SAM) formed by the araliphatic thiol (4-(4-(4-pyridyl)phenyl)phenyl)methanethiol leads to a concurrent rapid hydrogen evolution reaction (HER). The desorption process and resulting interfacial structure were investigated by voltammetric techniques, in situ spectroscopic ellipsometry, and in situ vibrational sum-frequency-generation (SFG) spectroscopy. Voltammetric experiments on SAM-modified electrodes exhibit extraordinarily high peak currents, which di er between Au(111) and polycrystalline Au substrates. Association of reductive desorption with HER is shown to be the origin of the observed excess cathodic charges. The studied SAM preserves its two-dimensional order near Au surface throughout a fast voltammetric scan even when the vertex potential is set several hundred millivolt beyond the desorption potential. A model is developed for the explanation of the observed rapid HER involving ordering and pre-orientation of water present in the nanometer-sized reaction volume between desorbed SAM and the Au electrode, by the structurally extremely stable monolayer, leading to the observed catalysis of the HER.
 
Article
The interactions of arsenic species with platinum and porous carbon electrodes were investigated with an electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry in alkaline solutions. It is shown that the redox reactions in arsenic-containing solutions, due to arsenic reduction/deposition, oxidation/desorption, and electrocatalyzed oxidation by Pt can be readily distinguished with the EQCM. This approach was used to show that the arsenic redox reactions on the carbon electrode are mechanistically similar to that on the bare Pt electrode. This could not be concluded with just classical cyclic voltammetry alone due to the obfuscation of the faradaic features by the large capacitative effects of the carbon double layer.For the porous carbon electrode, a continual mass loss was always observed during potential cycling, with or without arsenic in the solution. This was attributed to electrogasification of the carbon. The apparent mass loss per cycle was observed to decrease with increasing arsenic concentration due to a net mass increase in adsorbed arsenic per cycle that increased with arsenic concentration, offsetting the carbon mass loss. Additional carbon adsorption sites involved in arsenic species interactions are created during electrogasification, thereby augmenting the net uptake of arsenic per cycle.It is demonstrated that EQCM, and in particular the information given by the behavior of the time derivative of the mass vs. potential, or massogram, is very useful for distinguishing arsenic species interactions with carbon electrodes. It may also prove to be effective for investigating redox/adsorption/desorption behavior of other species in solution with carbon materials as well.
 
Article
This chapter focuses on multielectron reactions in organized assemblies of molecules at the liquid/liquid interface. We describe the thermodynamic and kinetic parameters of such reactions, including the structure of the reaction centers, charge movement along the electron transfer pathways, and the role of electric double layers in artificial photosynthesis. Some examples of artificial photosynthesis at the oil/water interface are considered, including water photooxidation to the molecular oxygen, oxygen photoreduction, photosynthesis of amphiphilic compounds and proton evolution by photochemical processes.
 
Article
Electrochemical deposition of crosslinked oxo-cyanoruthenate, Ru-O/CN-O, from a mixture of RuCl3 and K4Ru(CN)6 is known to yield a film on glassy carbon that promotes oxidations by a combination of electron and oxygen transfer. Layer-by-layer (LbL) deposition of this species and of a film formed by cycling of the electrode potential in a ZrO2 solution systematically increases the number of catalytically active sites of the Ru-O/CN-O on the electrode. The evaluation of the electrocatalytic activity was by cyclic voltammetric oxidation of cysteine at pH 2. Plots of the anodic peak current vs. the square root of scan rate were indicative of linear diffusion control of this oxidation, even in the absence of ZrO2, but the slopes of these linear plots increased with bilayer number, n, of (ZrO2 | Ru-O/CN-O) n . The latter observation is hypothesized to be due to an increased number of active sites for a given geometric electrode area, but proof required further study. To optimize utilization of the catalyst and to provide a size-exclusion characteristic to the electrode, the study was extended to LbL deposition of the composite in 50-nm pores of an organically modified silica film deposited by electrochemically assisted sol-gel processing using surface-bound poly(styrene sulfonate) nanospheres as a templating agent.
 
Article
A combination of direct electrochemical reduction and in-situ alkaline hydrolysis has been proposed to decompose energetic contaminants such as 1,3,5-Trinitroperhydro- 1,3,5-triazine and 2,4,6-Trinitrotoluene (RDX) in deep aquifers. This process utilizes natural groundwater convection to carry hydroxide produced by an upstream cathode to remove the contaminant at the cathode as well as in the pore water downstream as it migrates toward the anode. Laboratory evaluation incorporated fundamental principles of column design coupled with reactive contaminant modeling including electrokinetics transport. Batch and horizontal sand-packed column experiments included both alkaline hydrolysis and electrochemical treatment to determine RDX decomposition reaction rate coefficients. The sand packed columns simulated flow through a contaminated aquifer with a seepage velocity of 30.5 cm/day. Techniques to monitor and record the transient electric potential, hydroxide transport and contaminant concentration within the column were developed. The average reaction rate coefficients for both the alkaline batch (0.0487 hr-1) and sand column (0.0466 hr-1) experiments estimated the distance between the cathode and anode required to decompose 0.5 mg/L RDX to the USEPA drinking water lifetime Health Advisory level of 0.002 mg/L to be 145 and 152 cm.
 
Article
Battery systems have been developed that provide years of service for implantable medical devices. The primary systems utilize lithium metal anodes with cathode systems including iodine, manganese oxide, carbon monofluoride, silver vanadium oxide and hybrid cathodes. Secondary lithium ion batteries have also been developed for medical applications where the batteries are charged while remaining implanted. While the specific performance requirements of the devices vary, some general requirements are common. These include high safety, reliability and volumetric energy density, long service life, and state of discharge indication. Successful development and implementation of these battery types has helped enable implanted biomedical devices and their treatment of human disease.
 
Article
We report here the successful fabrication of an improved Bi film wrapped single walled carbon nanotubes modified glassy carbon electrode (Bi/SWNTs/GCE) as a highly sensitive platform for ultratrace Cr(VI) detection through catalytic adsorptive cathodic stripping voltammetry (AdCSV). The introduction of negatively charged SWNTs extraordinarily decreased the size of Bi particles to nanoscale due to electrostatic interaction which made Bi(III) cations easily attracted onto the surface of SWNTs in good order, leading to higher quality of Bi film deposition. The obtained Bi/SWNTs composite was well characterized with electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), the static water contact angle and the voltammetric measurements. The results demonstrates the improvements in the quality of Bi film deposited on the surface of SWNTs such as faster speed of electron transfer, more uniform and smoother morphology, better hydrophilicity and higher stripping signal. Using diethylene triaminepentaacetic acid (DTPA) as complexing ligand, the fabricated electrode displays a well-defined and highly sensitive peak for the reduction of Cr(III)-DTPA complex at -1.06 V (vs. Ag/AgCl) with a linear concentration range of 0-25 nM and a fairly low detection limit of 0.036 nM. No interference was found in the presence of coexisting ions, and good recoveries were achieved for the analysis of a river sample. In comparison to previous approaches using Bi film modified GCE, the newly designed electrode exhibits better reproducibility and repeatability towards aqueous detection of trace Cr(VI) and appears to be very promising as the basis of a highly sensitive and selective voltammetric procedure for Cr(VI) detection at trace level in real samples.
 
Article
Biological transformation of tetrachloroethylene (PCE) in silty clay samples by ionic injection of lactate under electric fields is evaluated. To prepare contaminated samples, a silty clay slurry was mixed with PCE, inoculated with KB-1(®) dechlorinators and was consolidated in a 40 cm long cell. A current density between 5.3 and 13.3 A m(-2) was applied across treated soil samples while circulating electrolytes containing 10 mg L(-1) lactate concentration between the anode and cathode compartments to maintain neutral pH and chemically reducing boundary conditions. The total adsorbed and aqueous PCE was degraded in the soil to trichloroethylene (TCE), cis-1,2-dichloroethene (cis-DCE), vinyl chloride (VC) and ethene in 120 d, which is about double the time expected for transformation. Lactate was delivered into the soil by a reactive transport rate of 3.7 cm(2) d(-1) V(-1). PCE degradation in the clay samples followed zero order transformation rates ranging from 1.5 to 5 mg L(-1) d(-1) without any significant formation of TCE. cis-DCE transformation followed first order transformation rates of 0.06 to 0.10 per day. A control experiment conducted with KB-1 and lactate, but without electricity did not show any significant lactate buildup or cis-DCE transformation because the soil was practically impermeable (hydraulic conductivity of 2×10(-7) cm s(-1)). It is concluded that ionic migration will deliver organic additives and induce biological activity and complete PCE transformation in clay, even though the transformation occurs under slower rates compared to ideal conditions.
 
Article
The oxygen exchange kinetics of platinum on yttria-stabilized zirconia (YSZ) was investigated by means of geometrically well-defined Pt microelectrodes. By variation of electrode size and temperature it was possible to separate two temperature regimes with different geometry dependencies of the polarization resistance. At higher temperatures (550–700 °C) an elementary step located close to the three phase boundary (TPB) with an activation energy of ∼1.6 eV was identified as rate limiting. At lower temperatures (300–400 °C) the rate limiting elementary step is related to the electrode area and exhibited a very low activation energy in the order of 0.2 eV. From these observations two parallel pathways for electrochemical oxygen exchange are concluded. The nature of these two elementary steps is discussed in terms of equivalent circuits. Two combinations of parallel rate limiting reaction steps are found to explain the observed geometry dependencies: (i) Diffusion through an impurity phase at the TPB in parallel to diffusion of oxygen through platinum – most likely along Pt grain boundaries – as area-related process. (ii) Co-limitation of oxygen diffusion along the Pt|YSZ interface and charge transfer at the interface with a short decay length of the corresponding transmission line (as TPB-related process) in parallel to oxygen diffusion through platinum.
 
SEM Data for (a) MWCNT-COOH, (b) Pt-MWCNT, (c) Pd-MWCNT; EDS data for (d) Pt-MWCNT and (e) Pd-MWCNT. 
TGA data for (a) MWCNT, (b) MWCNT-COOH, (c) Pt-MWCNT and (d) PdMWCNT.
average Ea values for the potential ranges studied for the nanohybrid modified carbon paste electrodes are as follows.
Article
Microwave induced reactions for immobilizing platinum and palladium nanoparticles on multiwall carbon nanotubes are presented. The resulting hybrid materials were used as catalysts for direct methanol, ethanol and formic acid oxidation in acidic as well as alkaline media. The electrodes are formed by simply mixing the hybrids with graphite paste, thus using a relatively small quantity of the precious metal. We report Tafel slopes and apparent activation energies at different potentials and temperatures. Ethanol electro-oxidation with the palladium hybrid showed an activation energy of 7.64 kJmol(-1) which is lower than those observed for other systems. This system is economically attractive because Pd is significantly less expensive than Pt and ethanol is fast evolving as a commercial biofuel.
 
Article
This review describes homogeneous and heterogeneous catalytic reduction of dioxygen with metal complexes focusing on the catalytic two-electron reduction of dioxygen to produce hydrogen peroxide. Whether two-electron reduction of dioxygen to produce hydrogen peroxide or four-electron O2-reduction to produce water occurs depends on the types of metals and ligands that are utilized. Those factors controlling the two processes are discussed in terms of metal-oxygen intermediates involved in the catalysis. Metal complexes acting as catalysts for selective two-electron reduction of oxygen can be utilized as metal complex-modified electrodes in the electrocatalytic reduction to produce hydrogen peroxide. Hydrogen peroxide thus produced can be used as a fuel in a hydrogen peroxide fuel cell. A hydrogen peroxide fuel cell can be operated with a one-compartment structure without a membrane, which is certainly more promising for the development of low-cost fuel cells as compared with two compartment hydrogen fuel cells that require membranes. Hydrogen peroxide is regarded as an environmentally benign energy carrier because it can be produced by the electrocatalytic two-electron reduction of O2, which is abundant in air, using solar cells; the hydrogen peroxide thus produced could then be readily stored and then used as needed to generate electricity through the use of hydrogen peroxide fuel cells.
 
Article
Polymer chain orientation in tensile-stretched poly(ethylene oxide)-lithium trifluoromethanesulfonate polymer electrolytes are investigated with polarized infrared spectroscopy as a function of the degree of strain and salt composition (ether oxygen atom to lithium ion ratios of 20:1, 15:1, and 10:1). The 1359 and 1352 cm(-1) bands are used to probe the crystalline PEO and P(EO)(3)LiCF(3)SO(3) domains, respectively, allowing a direct comparison of chain orientation for the two phases. Two-dimensional correlation FT-IR spectroscopy indicates that the two crystalline domains align at the same rate as the polymer electrolytes are stretched. Quantitative measurements of polymer chain orientation obtained through dichroic infrared spectroscopy show that chain orientation predominantly occurs between strain values of 150% and 250%, regardless of salt composition investigated. There are few changes in chain orientation for either phase when the films are further elongated to a strain of 300%; however, the PEO domains are slightly more oriented at the high strain values. The spectroscopic data are consistent with stretching-induced melt-recrystallization of the unoriented crystalline domains in the solution-cast polymer films. Stretching the films pulls polymer chains from the crystalline domains, which subsequently recrystallize with the polymer helices parallel to the stretch direction. If lithium ion conduction in crystalline polymer electrolytes is viewed as consisting of two major components (facile intra-chain lithium ion conduction and slow helix-to-helix inter-grain hopping), then alignment of the polymer helices will affect the ion conduction pathways for these materials by reducing the number of inter-grain hops required to migrate through the polymer electrolyte.
 
Article
Patterned copper sulfide (Cu(x)S) microstructures on Si (1 1 1) wafers were successfully fabricated by a relatively simple solution growth method using copper sulfate, ethylenediaminetetraacetate and sodium thiosulfate aqueous solutions as precursors. The Cu(x)S particles were selectively deposited on a patterned self-assembled monolayer of 3-aminopropyltriethoxysilane regions created by photolithography. To obtain high quality Cu(x)S films, preparative conditions such as concentration, proportion, pH and temperature of the precursor solutions were optimized. Various techniques such as optical microscopy, atomic force microscopy (AFM), X-ray diffraction, optical absorption and scanning electrochemical microscopy (SECM) were employed to examine the topography and properties of the micro-patterned Cu(x)S films. Optical microscopy and AFM results indicated that the Cu(x)S micro-pattern possessed high selectivity and clear edge resolution. From combined X-ray diffraction analysis and optical band gap calculations we conclude that Cu(9)S(5) (digenite) was the main phase within the resultant Cu(x)S film. Both SECM image and cyclic voltammograms confirmed that the Cu(x)S film had good electrical conductivity. Moreover, from SECM approach curve analysis, the apparent electron-transfer rate constant (k) in the micro-pattern of Cu(x)S dominated surface was estimated as 0.04 cm/s. The SECM current map showed high edge acuity of the micro-patterned Cu(x)S.
 
Article
The precipitation and growth of AgCl on silver in physiological NaCl solution were investigated. AgCl was found to form at bottom of scratches on the surface which may be the less effective sites for diffusion or the favorable sites for heterogeneous nucleation. Patches of silver chloride expanded laterally on the substrate until a continuous film formed. The ionic transport path through this newly formed continuous film was via spaces between AgCl patches. As the film grew, the spaces between AgCl patches closed and ion transport was primarily via micro-channels running through AgCl patches. The decrease of AgCl layer conductivity during film growth were attributed to the clogging of micro-channels or decrease in charge carrier concentration inside the micro-channels. Under thin AgCl layer, i.e. on the order of a micrometer, the dissolution of silver substrate was under mixed activation-Ohmic control. Under thick AgCl layer, i.e. on the order of tens of micrometers, the dissolution of silver substrate was mediated by the Ohmic resistance of AgCl layer.
 
Article
Substitution of a metal center of phosphomolybdate, PMo(12)O(40) (3-) (PMo(12)), or its tungsten analogue with dirhodium(II) and subsequent stabilization of gold nanoparticles, AuNPs, with Rh(2)PMo(11) is demonstrated. The AuNP-Rh(2)PMo(11) mediates oxidations but adsorbs too weakly for direct modification of electrode materials. Stability in quiescent solution was achieved by modifying glassy carbon (GC) with 3-aminopropyltriethoxysilane (APTES) and then electrostatically assembling AuNP-Rh(2)PMo(11). At GC|APTES|AuNP-Rh(2)PMo(11), cyclic voltammetry showed the expected set of three reversible peak-pairs for PMo(11) in the range -0.2 to 0.6 vs (Ag/AgCl)/V and the reversible Rh(II,III) couple at 1.0 vs (Ag/AgCl)/V. The presence of AuNPs increased the current for the reduction of bromate by a factor of 2.5 relative to that at GC|Rh(2)PMo(11), and the electrocatalytic oxidation of methionine displayed characteristics of synergism between the AuNP and Rh(II). To stabilize AuNP-Rh(2)PMo(11) on a surface in a flow system, GC was modified by electrochemically assisted deposition of a sol-gel with templated 10-nm pores prior to immobilizing the catalyst in the pores. The resulting electrode permitted determination of bromate by flow-injection amperometry with a detection limit of 4.0 × 10(-8) mol dm(-3).
 
Article
We investigate the oscillatory electro-oxidation of formic acid on platinum in a microchip-based dual-electrode cell with microfluidic flow control. The main dynamical features of current oscillations on single Pt electrode that had been observed in macro-cells are reproduced in the microfabricated electrochemical cell. In dual-electrode configuration nearly in-phase synchronized current oscillations occur when the reference/counter electrodes are placed far away from the microelectrodes. The synchronization disappears with close reference/counter electrode placements. We show that the cause for synchronization is weak albeit important, bidirectional electrical coupling between the electrodes; therefore the unidirectional mass transfer interactions are negligible. The experimental design enables the investigation of the dynamical behavior in micro-electrode arrays with well-defined control of flow of the electrolyte in a manner where the size and spacing of the electrodes can be easily varied.
 
Article
Here we review the recent applications of ion transfer (IT) at the interface between two immiscible electrolyte solutions (ITIES) for electrochemical sensing and imaging. In particular, we focus on the development and recent applications of the nanopipet-supported ITIES and double-polymer-modified electrode, which enable the dynamic electrochemical measurements of IT at nanoscopic and macroscopic ITIES, respectively. High-quality IT voltammograms are obtainable using either technique to quantitatively assess the kinetics and dynamic mechanism of IT at the ITIES. Nanopipet-supported ITIES serves as an amperometric tip for scanning electrochemical microscopy to allow for unprecedentedly high-resolution electrochemical imaging. Voltammetric ion sensing at double-polymer-modified electrodes offers high sensitivity and unique multiple-ion selectivity. The promising future applications of these dynamic approaches for bioanalysis and electrochemical imaging are also discussed.
 
Article
It is demonstrated through the cathodic reduction of nickel manganese spinels of Ni0,6Mn2,4O4 formulae that is possible to increase the electrochemical reduction by replacement of manganese ions and nickel ions by copper ions. The best performance is shown by Cu0,5Ni0,5Mn2O4 spinel. The study of some physicochemical properties of oxides let us to know the tetrahedral and octahedral sites. The reduction reaction occur on octahedral sites formed by Mn4+ ions associated with Mn3+ ions. The electrochemical reactivity of oxides is likely to occur through the redox processes in solid state between nickel (II) and manganese (III) ions on octahedral sites on the one hand, and between octahedral copper (II) and tetrahedral manganese (III) ions on the other hand. These redox processes in solid state are coupled with the electrochemical reduction of the oxides studied.
 
Article
Effects of sulphate (SO42−) ion additives on the pitting corrosion of pure aluminium (Al) have been investigated in aqueous 0.01 M NaCl solution as a function of SO42− ion concentration using potentiodynamic polarisation experiment, ac impedance spectroscopy, electrochemical quartz crystal microbalance technique and abrading electrode technique. The addition of SO42− ions to NaCl solution raised the pitting potential (Epit) of pure Al in value and simultaneously the anodic current density at potentials much higher than the Epit on the polarisation curves. This implies that SO42− ions impede the initiation of pit on pure Al surface below the Epit, but enhance the growth of pre-existing pits, which is validated by optical microscopy. It was found that the values of the Cl− ion-incorporated outer film resistance Rout,ox in SO42− ion-containing chloride solutions were much lower than those in SO42− ion-free solution, obtained from the impedance spectra measured at potentials below the Epit. The chloride peak disappeared from the Auger spectra in SO42− ion-containing solutions. The mass decay rate and pit growth rate b were observed to increase in values once the pits were formed in SO42− ion-containing chloride solutions. Based upon the above experimental results, it is suggested that SO42− ions retard the oxide film breakdown by Cl− ion incorporation into the film, while they accelerate the Al metal dissolution through the instantaneous formation of tunnels at the bottom of the pre-existing pits after the exposure of bare surface above the Epit.
 
Article
For (Ti1−xVx)2Ni (x = 0.05, 0.1, 0.15, 0.2 and 0.3) ribbons, synthesized by arc-melting and subsequent melt-spinning techniques, an icosahedral quasicrystalline phase was present, either in the amorphous matrix or together with the stable Ti2Ni-type phase. With increasing x values, the maximum discharge capacity of the alloy electrodes increased until reached 271.3 mAh/g when x = 0.3. The cycling capacity retention rates for these electrodes were approximately 80% after a preliminary test of 30 consecutive cycles of charging and discharging. Ti1.7V0.3Ni alloy electrode displayed the best high-rate discharge ability of 82.7% at the discharge current density of 240 mA/g.
 
Article
The LiNi0.5−xMn0.5−xCo2xO2 (0 < x ≤ 0.1) series was first prepared at 800 °C by the spray dry method. The structural and electrochemical characteristics of these compounds were also studied. The Co substitution seems to promote the formation of LiNi0.5−xMn0.5−xCo2xO2. In addition, the Co introduction in LiNi0.5Mn0.5O2 can not only reduce the cell polarization, but increase the reversible capacity. The LiNi0.5−xMn0.5−xCo2xO2 series shows an excellent cyclability and rate ability. After 50 cycles, LiNi0.425Mn0.425Co0.15O2 shows a reversible capacity of about 110 mAh g−1 at the rate of 1 mA cm−2 (100 mA g−1) in 3–4.6 V at room temperature and more than 140 mAh g−1 at the rate of 2 mA cm−2 (200 mA g−1) at 55 °C.
 
Article
The inhibition of Cu corrosion in 0.1 M NaCl solution was studied using the EQCM technique. Some organic compounds, at 10−3 M concentration, were tested as inhibitors. The inhibiting effect of these additives was evaluated by recording the anodic and cathodic polarization curves on Cu, electroplated on quartz crystals. At the same time the mass changes of the electrode, as a function of the potential, were recorded. The formation of the protective film during immersion in distilled water or 0.1 M NaCl solution containing the inhibitors was followed by variation of the EQCM frequency. The protective characteristics of these films were evaluated by the mass variations of the electrode immersed in 0.1 M NaCl solution and by the voltammograms recorded after 1 min or 5 h immersion in 0.1 M NaCl solution. FTIR reflection spectra were recorded on Cu sheets immersed for 1 or 60 min in NaCl solution in the presence of inhibitors. They showed a very rapid interaction between metal surface and organic molecule. The results obtained allow us to conclude that EQCM technique has a valuable part to play in the interpretation of corrosion and corrosion inhibition mechanisms.
 
Article
The hydrogen absorption and diffusion into and through a palladium membrane electrode has been investigated in 0.1 M LiOH solution by using an ac impedance method combined with an electrochemical hydrogen permeation technique. The ac impedance measurements were carried out in the overpotential range of −0.07 to 0.28 V(rhe) applied to the cathodic side of the palladium membrane after the hydrogen permeation achieved a steady-state. The experimental impedance spectra were analysed by using complex non-linear least squares (CNLS) fitting method on the basis of two Faradaic hydrogen absorption admittance equations derived in the preceding work. As a result, the indirect hydrogen absorption model accounts for the impedance spectra measured in the overpotential range of 0.1–0.28 V(rhe), whereas the direct absorption model dominates the absorption at the overpotentials below 0.08V(rhe), accompanied by the anomalous behaviour of hydrogen permeation transients. Under the assumption of tridimensional hydrogen adsorption on the palladium electrode, the hydrogen coverage was theoretically calculated as a function of overpotential with the kinetic rate constants of Volmer adsorption, hydrogen absorption reaction and the hydrogen diffusivity in palladium, best-fitted to the measured impedance spectra. The calculated hydrogen coverage suggested the formation of β-phase palladium hydride at the overpotentials below 0.08 V(rhe). The model change to the direct hydrogen absorption, accompanied by the anomalous hydrogen permeation, accounts for the formation of β-palladium hydride at the overpotential of 0.08 V(rhe).
 
Article
The hot corrosion behavior of the Ni-based superalloy M38G covered with a film of molten 0.9Na2SO4–0.1K2SO4 (mole fraction) has been studied by electrochemical impedance spectroscopy at 900 °C in air. For comparison, the corrosion of the alloy immersed in molten (Na,K)2SO4 was also examined. The electrochemical impedance spectra in deep molten salt during an initial stage consisted of a semicircle at high frequency and a line at low frequency indicating a diffusion-controlled reaction. With extended immersion the impedance spectra were composed of two capacitive loops, i.e., a small semicircle at high-frequency port, and a large one at low-frequency port. The change of the impedance spectra is related to the formation of a protective scale. Contrary to the corrosion in deep molten salt, the corrosion of the alloy in the presence of a film of fused salt presented the characteristics of two capacitive loops for all the duration of the experimental test. Equivalent circuits representing the corrosion of the alloy in both corrosion conditions are proposed to fit the impedance spectra and electrochemical parameters in the equivalent circuits are also calculated.
 
Article
In the last few years great efforts have been made in order to find environmentally friendly substitutes for Cr6+ pre-treatments applied to aluminium alloys used in the aircraft industry. In this work we have investigated the electrochemical response of a bilayer pre-treatment consisting of a Ce conversion bottom layer and a non-functional silane (bis-1,2-(triethoxysilyl) ethane (BTSE)) top layer applied on Al 2024-T3, and compared its behaviour with monolayer coated samples. The investigation was carried out in 0.1 M NaCl solution, and the electrochemical techniques employed were anodic polarization curves and electrochemical impedance spectroscopy (EIS). EIS experiments performed with bilayer coated samples have shown a continuous increase of the impedance response during the whole test period, which was interpreted on the basis of a pore blocking mechanism supported by scanning electron microscopy (SEM) images and equivalent circuit fitting. Moreover, the impedance of the bilayer coated samples was approximately one order of magnitude higher than that presented by monolayer coated ones. On the other hand, mechanical tests have evidenced the good adhesion of the silane layer to the Ce conversion layer, which can be likely attributed to a better linking between the silane molecules and the cerium bottom layer.
 
Article
The electrochemical properties of Pd(1 1 1), Pd(1 0 0) and Pd(1 1 0) single crystal bead electrodes, prepared by a novel electron beam heating and inductive annealing technique, have been characterized in 0.1 M sulfuric acid and 0.1 M perchloric acid by cyclic voltammetry and chronoamperometry. Hydrogen and (hydrogen) sulfate adsorption as well as surface oxidation were found to depend strongly on the crystallographic orientation and the nature of the electrolyte. The combination of charge displacement and voltammetric experiments allowed the determination of the potentials of zero total charge (Epztc) of Pd(1 1 1) and Pd(1 0 0). The values of Epztc in sulfuric acid were found to be more negative than in perchloric acid. The estimation of Epztc for Pd(1 1 0) was hampered by the superposition with hydrogen absorption. The electro-oxidation of irreversible adsorbed carbon monoxide monolayers was studied on the three low-index Pd electrodes. The onset potential of the CO oxidation reaction follows the sequence Pd(1 0 0) < Pd(1 1 0) < Pd(1 1 1). Chronoamperometric experiments revealed a pronounced structure sensitivity of the reaction kinetics. The processes involved are determined by nucleation of oxygen-containing species on defect (step) sites and by slow diffusion of COads on (1 1 1) terrace sites.
 
Article
In the present work, the mechanism of charging/discharging at the amorphous manganese oxide electrode was investigated in 0.1 M Na2SO4 solution with respect to amount of hydrates and valence (oxidation) states of manganese using a.c.-impedance spectroscopy, anodic current transient technique and cyclic voltammetry. For this purpose, first the amorphous manganese oxide film was potentiostatically electrodeposited, followed by heat-treatment at 25–400 °C to prepare the electrode specimen with different amounts of hydrates and oxidation states of manganese. For as-electrodeposited electrode with the most hydrates, the anodic current transient clearly exhibited a linear relationship between the logarithm of current density and the logarithm of time, with a slope of −0.5, indicating that the charging/discharging is purely limited by Na+/H+ ion diffusion. From the analyses of the impedance spectra combined with anodic current transients measured on the hydrated electrode heat-treated at 25–150 °C, it was found that as the amount of hydrates decreases, the depth of cation diffusion in the electrode becomes shallower and the ratio of charge-transfer resistance to diffusion resistance also increases. This suggests that a transition occurs of pure diffusion control to a mixed diffusion and charge-transfer reaction control. For the dehydrated electrode heat-treated at 200–400 °C, the charging/discharging purely proceeds by the charge-transfer reaction. The reversibility of the redox reaction increases with increasing amount of hydrates and oxidation states of manganese, which provides us the higher power density. On the other hand, the pseudocapacitance decreases in value with increasing heat-treatment temperature, thus causing the lower energy density.
 
Article
The electrochemical behavior of tin-doped indium oxide (ITO) on SiO2 in 0.3 M HCl was studied using voltammetric scanning method. The result showed that an obvious reduction current peak occurred during the first cathodic potential scanning. The reduction reaction became less active after annealing ITO at 500 °C for 1 h. The result was attributed to the replenishment of oxygen-deficient site, which acts as current carrier, by the annealing treatment. Many spherical In–Sn particles with sizes about 100–500 nm were formed on the ITO surface adjacent to the grain boundary when the reduction current took place. The In–Sn particles initiated preferentially on the ITO surface near grain boundaries attending the dissolution of ITO grain boundary. In the scanning period, after completion of the reduction current peak, reduction of hydrogen ions occurred in more negative potential region. A schematic illustration for the formation mechanism of the In–Sn reduction particle was postulated based on the metallographical and electrochemical results in this work.
 
Article
Composite G/PPy/PPy(La1−xSrxMnO3)/PPy electrodes made of the perovskite La1−xSrxMnO3 embedded into a polypyrrole (PPy) layer, sandwiched between two pure PPy films, electrodeposited on a graphite support were investigated for electrocatalysis of the oxygen reduction reaction (ORR). PPy and PPy(La1−xSrxMnO3) (0≤ x ≤0.4) successive layers have been obtained on polished and pretreated graphite electrodes following sequential electrodeposition technique. The electrolytes used in the electrodeposition process were Ar saturated 0.1 mol dm−3 pyrrole (Py) plus 0.05 mol dm−3 K2SO4 with and without containing a suspension of 8.33 g L−1 oxide powder. Films were characterized by XRD, SEM, linear sweep voltammetry, cyclic voltammetry (CV) and electrochemical impedance (EI) spectroscopy. Electrochemical investigations were carried out at pH 12 in a 0.5 mol dm−3 K2SO4 plus 5 mmol dm−3 KOH, under both oxygenated and deoxygenated conditions. Results indicate that the porosity of the PPy matrix is considerably enhanced in presence of oxide particles. Sr substitution is found to have little influence on the electrocatalytic activity of the composite electrode towards the ORR. However, the rate of oxygen reduction decreases with decreasing pH of the electrolyte from pH 12 to pH 6. It is noteworthy that in contrast to a non-composite electrode of the same oxide in film form, the composite electrode exhibits much better electrocatalytic activity for the ORR.
 
Article
In the present study, different types of 75% Cr3C2–25% NiCr coatings were applied on a steel substrate by means of high velocity oxygen fuel spraying (HVOF), and studied using ac and dc electrochemical measurements in an aerated and unstirred 0.5 M H2SO4 solution. Structural characterization was determined before and after electrochemical tests. Differences between all sprayed systems are related to the gun transverse speed and number of deposited layers, which strongly affected the electrochemical characteristics of the coated steels. The coating obtained with a higher torch speed showed better resistance against corrosion. The electrochemical impedance results were analyzed using an equivalent circuit where porosity of the coatings and substrate oxidation were considered.
 
Article
Closely packed self-assembled monolayers of alkanethiols (CnT) adsorbed on the copper surface are applicable as protective films against copper corrosion in aerated aqueous solution and atmospheric environments. They act as barrier to oxygen diffusion, since the cathodic process of copper corrosion is suppressed by coating the surface with the CnT monolayer. Diffusion process of molecular oxygen dissolved in 0.5 M Na2SO4 within the CnT self-assembled monolayer adsorbed on copper was investigated by hydrodynamic voltammetry. The diffusion process within the monolayer films of C10T ~ C18T was explained by the permeation model, while a combination of the permeation model with the defect model was applied to diffusion of oxygen within the C6T and C8T monolayer films. Because of the wettability at the film surface, hydrated oxygen molecules could enter into the 11-mercapto-1-undecanol self-assembled monolayer without difficulty.
 
Article
Aniline derivatives, namely 2-chloroaniline, 2-fluoroaniline, 2-aminophenetole, 2-ethylaniline, o-aminoanisole and o-toluidine were studied for their possible use as copper corrosion inhibitors in 0.5 M HCl. These compounds were studied in concentrations from 10−3 to 10−4 M at temperature 298 K. Effectiveness of these compounds was assessed through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. These compounds inhibit the corrosion of copper in HCl solution to some extent. In each case, inhibition efficiencies increase with increasing concentration. A suggested model for the interface as well as some kinetic data is presented. These inhibitors obey the Temkin adsorption isotherm. A correlation between structure and inhibition efficiencies is suggested.
 
Article
The effect of ppm level of chloride and fluoride ions on the dissolution of electrochemically deposited Pt with two different thickness has been studied by using electrochemical quartz crystal microbalance (EQCM) and ICP-Mass analysis in combination with atomic force microscopy (AFM). A mass loss due to dissolution of Pt as chloride complexes was observed in as low as 10 ppm [Cl−] at 1.06 V versus SHE. Fluoride ion did not have any effect on the dissolution of Pt in as high as 1000 ppm [F−]. From the comparison of EQCM, ICP-Mass and AFM images, it was revealed that amount of platinum dissolution under potential cycling greatly depended on chloride concentration and morphology of deposited Pt layers. When Pt dissolution was induced by Cl− ions, the amount of dissolved Pt did not depend on the particle size of the deposited Pt. On the other hand, in the absence of Cl− induced dissolution, i.e. when oxide formation was dominant, the particle size of the deposited Pt greatly affected the amount of dissolved Pt. This was explained by considering the increase of overpotential for the reduction of chloride complex due to its high stability in chloride solution.
 
Article
The electrochemical behaviour of Cu, Cu-Al and Cu-Al-Ag alloys in aqueous solutions of NaCl (0.5 M, pH = 3.00) was studied by means of voltammetric methods and electrochemical impedance spectroscopy. The surfaces were examined by SEM and EDX analysis. Cu-Al-Ag alloy shows a potentiodynamic behaviour similar to that of the pure copper electrode while the Cu-Al alloy presents some minor differences. In the active dissolution region the electrodes suffer pitting corrosion and in the other potential regions there are the formation of a passivant film with composition depending on the potential. The impedance responses of the electrodes are discussed. An electrodissolution mechanism is proposed and the effect of the alloying elements upon the impedance response and polarisation curves is explained. The main effects are due to the production of copper and silver chlorides and aluminium oxides/ hydroxides at the corroding interface. The addition of Al or (Al + Ag) increases the corrosion resistance of pure copper.
 
Article
LixMn2O4 (LMO) and LixMn2O4–0.5ZrO2 (LMZO) thin films have been fabricated by radio-frequency (rf) sputtering deposition combined with conventional annealing method. The structures and surface morphology of thin films are characterized by X-ray diffraction, transmission electron microscopy, selected area electron diffraction and scanning electron microscopy techniques. It is shown that the addition of mass quantity of ZrO2 in LMZO can control the grain growth of nano-crystalline LMO. The electrochemical performances of all-solid-state thin film lithium batteries (TFBs) based on these thin films as cathodes are examined by cyclic voltammetry (CV), galvanostatic mode and alternate-current impedance measurements. Our results demonstrated that the addition of electrochemically inactive ZrO2 could significantly overcome the disadvantage of two distinct plateaus in 3 and 4 V regions. LMZO is expected to become a promising cathode material for future TFBs.
 
Article
Molybdenum oxide-based conversion coatings have been formed on the surface of the depleted uranium–0.75 wt% titanium alloy using either concentrated nitric acid or fluorides for surface activation prior to coating formation. The acid-activated surface forms a coating that offers corrosion protection after a period of aging, when uranium species have migrated to the surface. X-ray photoelectron spectroscopy (XPS) revealed that the protective coating is primarily a polymolybdate bound to a uranyl ion. Rutherford backscattering spectroscopy (RBS) on the acid-activated coatings also shows uranium dioxide migrating to the surface. The fluoride-activated surface does not form a protective coating and there are no uranium species on the surface as indicated by XPS. The coating on the fluoride-activated samples has been found to contain a mixture of molybdenum oxides of which the main component is molybdenum trioxide and a minor component of an Mo(V) oxide.
 
Article
Molybdenum oxide based conversion coatings have been formed on the surface of the depleted uranium–0.75 wt.% titanium alloy. Electrochemical impedance spectroscopy (EIS) measurements have been performed on the as-made and aged coatings and compared with the untreated depleted uranium (DU) alloy. The Nyquist and Bode plots of the as-made coating were similar to the untreated samples and contained capacitive and inductive loops. The aged coating exhibits significantly different behavior from the as-made coating and has been modeled with a four element equivalent circuit that contains a constant phase element (CPE).
 
Article
The nature of the anodic oxide film that forms on titanium on titanium in 0.9% NaCl has been investigated using a wide range of techniques. A linear relationship was found between the critical current density required for passivation of titanium in 0.9% NaCl and the sweep rate. Anodic oxide films formed on titanium in 0.9% NaCl appear to consist of two layers, an inner compact layer, the growth of which continues to follow a high field growth law, and a porous less protective outer porous layer. XPS and XRD indicated that passive films on titanium consist mainly of TiO2. However, hydroxides and lower oxides are also present, especially in rapidly grown films. XRD data indicated that in 0.9% NaCl the anodic oxide film is formed through the preferential removal atoms in the plane of (0 0 2) in the course of electrochemical reaction. A model based analysis XPS spectra was proposed to explain the growth rate dependence of the degree of protection offered by anodic oxide films on titanium. XPS clearly demonstrated the present of Ti(III) and Ti(II) cations in the passive film. This is strong evidence that cation migration more likely dominates over anion migration in the growth mechanism of anodic oxide film. XPS data also revealed that the concentrations of Ti(III) and Ti(II) species within the oxide films increased as the oxide/metal interface was approached.
 
Article
Electroless ZnO deposition on a glass substrate from dissolved oxygen-free aqueous solutions containing Zn(NO3)2 and dimethylamineborane (DMAB) was examined to yield ZnO films applicable to a transparent conducting oxide (TCO). Concentration of Zn(NO3)2 was optimized in terms of crystal growth orientation and surface morphology using XRD and AFM, and that ranging from 0.065 to 0.075 M was found to provide well 〈0 0 0 1〉-oriented dense ZnO films. The polycrystalline ZnO films deposited with Zn(NO3)2 concentration of 0.07 M had a preferred 〈0 0 0 1〉 growth orientation and exhibited high visible transparency. Top-view and cross-sectional FE-SEM images revealed that hexagonal columnar ZnO grains with 200 nm in diameter and 290 nm in length grew almost vertically from a glass substrate. Heat treatment at 723 K under a reductive atmosphere was performed to increase the intrinsic carrier concentration in the ZnO film, and Hall effect measurements revealed low electrical resistivity of 4.7 × 10−3 Ω cm.
 
Article
We present scanning tunneling microscopy data on the dynamics of monatomic high islands on gold electrodes in different electrolytes. From a statistical analysis of the island fluctuations around the equilibrium shape and from the investigation of the local perimeter curvature of the latter we determine the step line tension and the kink energy of gold islands on an Au(0 0 1) surface as a function of the electrode potential. We find that in chloric acid the step line tension is smaller than for Au(0 0 1) in sulfuric acid, however, the kink energy is much higher which leaves us with the puzzling result that island fluctuations are large, however, island edges are comparatively straight. Both energies show merely a weak dependence on the electrode potential in contrast to our previous findings in sulfuric acid. Furthermore, by analyzing the relaxation time of island coalescence events we determine the dominant mass transport on the Au(0 0 1) electrode to be terrace diffusion where the time limiting step of the migration process is the creation of transport species at the island edge rather than the hopping of species on the surface. This is in apparent contradiction to previous results from island decay studies where a diffusion limited terrace diffusion was found. All results can be explained if one assumes that the relevant mass transport species on Au(0 0 1) in chloride containing electrolytes are larger (linear) structure units rather than single adatoms. Possible candidates for these units are Au-Cl complexes.
 
Article
Using impedance spectroscopy, we determined the step dipole moment and the potential dependence of the step line tension of silver electrodes in contact with an electrolyte: (0 0 1) and vicinal surfaces (1 1 n) with n = 5, 7, 11 in 10 mM ClO4−-solutions were investigated. The step dipole moment is determined from the shift of the potential of zero charge (pzc) as a function of the surface step density. The dipole moment per step atom was found to be 3.5 ± 0.5 × 10−3 e Å. From the pzc and the potential dependence of the capacitance curves, the potential dependence of the surface tension of the vicinal surfaces is determined. The line tension of the steps is then calculated from the difference between the surface tensions of stepped (1 1 n) and the nominally step-free (0 0 1) surfaces. The results are compared to a previous study on Au(1 1 n) surfaces. For gold, the step line tension decreases roughly linear with potential, whereas a parabolic shape is observed for silver.
 
Article
While soluble in many organic solvents, bipyridilium systems typified here by cyanophenyl-paraquat (CPQ) often deposit the mono-reduced and di-reduced species in a manner dependent on anion, with attendant complexity of electrochemistry. Factors governing this important electrochromic process for CPQ are examined by cyclic voltammetry and spectroelectrochemical study. The outcome appears to be the resultant of lattice forces, charge-transfer interaction, and the anion role in CPQ (dication) micellisation.
 
Article
Copper strike baths are extensively used in metal plating industry as they present the ability to plate adherent copper layers on less-noble metal substrates such as steel and zinc die castings. However, in the last few years, due to environmental controls and safety policies for operators, the plating industry has been interested in replacing the toxic cyanide copper strike baths with environmentally friendly baths. A broad bibliographic review showed that the published papers, referring to the new nontoxic copper strike baths, are patents, having little or no emphasis focused on electrodeposition mechanisms. Therefore, it was decided to study the copper electrodeposition mechanism from a strike alkaline bath prepared with one of the most nontoxic chelating agents cited in many patents which is the 1-hydroxyethane-1,1-diphosphonic acid, known as HEDP. This acid forms very stable water soluble complexes with Cu2+ ions, thus cupric sulfate was used for preparing the plating bath. The results obtained through a cyclic voltammetry technique showed that Cu2+ ion reduction to Cu from an HEDP electrodeposition bath occurs via a direct reduction reaction without a formation of Cu+ intermediates.
 
Article
Direct anodic oxidation of (S)-(−)-1,1′-bi-2-naphthol dimethyl ether (BNME) in CH2Cl2/CHCl3 containing boron trifluoride diethyl etherate (BFEE) as the supporting electrolyte led to facile electrodeposition of high-quality free-standing poly((S)-(−)-1,1′-bi-2-naphthol dimethyl ether) (PBNME) film on stainless steel (SS)/indium tin oxide (ITO) electrodes. As-formed PBNME films showed good electroactivity and redox stability in CH2Cl2–BFEE, BFEE, and even in concentrated sulfuric acid. Both doped and dedoped PBNME films were partly soluble in strong polar solvents, such as dimethyl sulfoxide (DMSO). Quantum chemistry calculations of BNME and FT-IR spectrum of dedoped PBNME films demonstrated that the polymerization probably occurred at 4- and 4′-positions. Optical rotation determination showed that the conformation of the monomer was maintained during the electrochemical polymerization process and the polymer exhibited greatly enhanced optical rotation value with main chain axial chirality compared with that of the monomer. Fluorescent spectral studies indicated that soluble PBNME was a good blue-light emitter with maximum emission at 415 nm and fluorescence quantum yield of 0.15, while solid-state PBNME film showed its emission centered at 380 nm. Furthermore, as-formed PBNME manifested favorable thermal stability and relatively high electrical conductivity of about 10−1 S cm−1 at room temperature.
 
Article
This paper describes the partitioning equilibrium of 1,1′-dibenzyl-4,4′-bipyridinium cation (BV2+) between aqueous electrolytes and Nafion films, and the influence of BV2+–Nafion interaction on the rate of charge transport in loaded films. The voltammetric charge measured at BV2+-loaded film electrodes demonstrated that the redox ion was highly concentrated in the polyanionic film from its dilute aqueous solution. An electrochemically poor response of highly loaded polymers resulted from the deactivation of the incorporated BV2+, which was due to the dehydration of the polymer. Although hydrophobic interactions contributed to some extent to bind the redox species to the polymer, the reduced positive charge of the redox species weakened the binding. Thus, an electrostatic interaction between them is a major factor determining the incorporation of BV2+ into the polymer. The impedance response of the loaded film electrodes was consistent with the behavior expected for the diffusion of charge carriers through a layer of finite thickness. When the surface concentration of BV2+ increased from 2 to 40 nmol cm−2, the apparent diffusion coefficient for charge transport decreased by a factor of 14. This dependence indicates a primary role of the physical diffusion of BV2+ in charge transport through the film. A decrease in the BV2+ mobility with increased loading arises probably from the ionic association between incorporated redox ions and polymer sulfonate groups, which are caused by a reduction in the film permittivity induced by cation exchange.
 
Article
A novel conducting polymer was successfully synthesized via electropolymerization of 1-(1H-pyrrol-1-yl)-2,5-di(thiophen-2-yl)-1H-pyrrole. The electrochemical and electro-optical properties of the corresponding polymer, which was the first example of polymer containing 1,1′-bipyrrole units, were elaborated using electroanalytical and spectroscopic techniques. Cyclic voltammograms and electro-optical studies showed that the polymer has a stable and well-defined reversible redox process as well as electrochromic behavior. The processable polymer film also possessed a yellowish orange light emitter property.
 
Top-cited authors
Bernard Tribollet
  • French National Centre for Scientific Research
Rüdiger Kötz
  • Paul Scherrer Institut
Doron Aurbach
  • Bar Ilan University
Mario G S Ferreira
  • University of Aveiro
Mark E. Orazem
  • University of Florida