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Showing papers in "Journal of Applied Electrochemistry in 1998"


Journal ArticleDOI
TL;DR: Magneli phases are a range of substoichiometric oxides of titanium of the general formula TinO2n−1, (where n is between 4 and 10) produced from high temperature reduction of titania in a hydrogen atmosphere as discussed by the authors.
Abstract: Magneli phases are a range of substoichiometric oxides of titanium of the general formula TinO2n−1, (where n is between 4 and 10) produced from high temperature reduction of titania in a hydrogen atmosphere These blue/black ceramic materials exhibit a conductivity comparable to that of graphite and can be produced in a number of forms, such as tiles, rods, fibres, foams and powders While these materials have been studied for many years, they have only recently received interest for use as ceramic electrode materials, commercially termed ‘Ebonex®’, and are beginning to challenge precious metal coated anodes for some applications in aggressive electrolytes Other uses for these materials include electrowinning, electroplating, battery materials, impressed current cathodic protection anodes, electrochemical soil remediation, oxidation of organic wastes, flexible cable materials and electrophoresis The scope of this review considers the structure and properties of Magneli phase titanium oxide materials, together with their electrochemical behaviour and applications

273 citations


Journal ArticleDOI
TL;DR: In this paper, a method of measuring current distribution in a polymer electrolyte fuel cell of active area 100cm2 has been demonstrated, using a printed circuit board (PCB) technology to segment the current collector and flow field.
Abstract: A new method of measuring current distribution in a polymer electrolyte fuel cell of active area 100cm2 has been demonstrated, using a printed circuit board (PCB) technology to segment the current collector and flow field. The PCB technique was demonstrated to be an effective approach to fabricating a segmented electrode and provide a useful tool for analysing cell performance at different reactant gas flow rates and humidification strategies. In this initial chapter of work with the segmented cell, we describe measured effects on current distribution of cathode and anode gas stream humidification levels in a hydrogen/air cell, utilizing a NafionTM 117 membrane and single serpentine channel flow fields, and operating at relatively high gas flow rates. Effects of the stoichiometric flow of air are also shown. A clear trend is seen, apparently typical for a thick ionomeric membrane, of lowering in membrane resistance down the flow channel, bringing about the highest local current density near the air outlet. This trend is reversed at low stoichiometric flows of air. At an air flow rate less than three times stoichiometry, the local performance starts to drop significantly from inlet to outlet, as local oxygen concentration drop overshadows the lowering in resistance along the direction of flow.

264 citations


Journal ArticleDOI
TL;DR: In this article, pore formers are added to the electrocatalyst slurry which is used for the hot spraying process to obtain additional coarse porosity for better access of oxygen from air to the depth of the cathode.
Abstract: Better performance of and higher electrocatalyst utilization in proton-exchange membrane fuel cells equipped with thin film electrodes is achieved by exploiting pore forming additives in the electrode recipe formulation. Preparing the membrane–electrode assembly by a hot spraying procedure already provides 35% porosity. Additional coarse porosity is obtained by adding pore formers to the electrocatalyst slurry which is used for the hot spraying process. This allows for a better access of oxygen from air to the depth of the cathode. For air operation at ambient pressure and low catalyst loading of 0.15mgPtcm-2 a current density of 200mAcm-2 at 0.7V cell voltage can be obtained with such electrodes.

163 citations


Journal ArticleDOI
TL;DR: In this paper, the composition, crystal structure and deposition rate of NiCoB alloys were determined as a function of the concentration of reducing agent (dimethylamineborane) and complexing agents (tartrate, citrate, malonate and succinic acid).
Abstract: Fundamental aspects of electroless Ni–B, Co–B and Ni–Co–B alloys have been systematically examined. The composition, crystal structure and deposition rate of the alloys were determined as a function of the concentration of reducing agent (dimethylamineborane) and complexing agents (tartrate, citrate, malonate and succinic acid), bath pH and Ni2+/Co2+ ratio. Changes in the deposition rate and metallurgical features of the alloys induced by the change in plating parameters are discussed, based on electrochemical polarization data and the formation enthalpy of the nickel and cobalt borides.

156 citations


Journal ArticleDOI
TL;DR: In this article, the long term behavior of two 100kW proton exchange membrane (PEM) water electrolyser plants is analysed, showing that the Nafion® 117 membrane is the weakest part in a PEM electrolyser regarding long term performance.
Abstract: The long term behaviour of two 100kW proton exchange membrane (PEM) water electrolyser plants is analysed. The systems had to be shut down due to problems with excessive levels of hydrogen in the oxygen product stream. The time to breakdown was different by a factor of nearly 10 from plant to plant. Post mortem analysis of the cell stacks revealed that the Nafion® 117 membrane is the weakest part in a PEM electrolyser regarding long term performance. Substantial thinning of the membranes in the stacks was detected. The degradation process was found to depend on the position within an individual cell, as well as of the position of the cell in the electrolyser stack. The dissolution process proceeds from the interface between the cathode and the membrane, is not specific with respect to the ion exchange groups, and is most likely triggered and/or enhanced by local stress on the membrane.

139 citations


Journal ArticleDOI
TL;DR: In this article, the structure and wettability of pasted zinc electrodes were optimized for the development of a long-lived, electrically rechargeable zinc-air battery, and the effect of discharge rate on cell voltage and delivered capacity, as well as the maximum power were measured.
Abstract: For the development of a long-lived, electrically rechargeable zinc–air battery the structure and wettability of pasted zinc electrodes were optimized. Pasted zinc electrodes containing 1 to 10% cellulose but having almost the same nominal capacities were prepared and tested in zinc/oxygen cells. The effect of discharge rate on cell voltage and delivered capacity, as well as the maximum power, were measured. Furthermore, cell charge–discharge behaviour and cycle life were examined. After different times of operation, the porosity and the pore size distribution of the pasted zinc electrodes were measured by means of mercury porosimetry. The cycle life and peak power drain capability of the Zn/oxygen battery could be substantially improved by the addition of 10wt% cellulose to the pasted zinc electrode.

137 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the kinetics and mechanism of electrooxidation of Mn2+ ions to MnO2 (EMD) using cyclic voltammetry at 80°C.
Abstract: The kinetics and mechanism of electrooxidation of Mn2+ ions to MnO2 (EMD) has been studied in electrolytes comprising MnSO4 and H2SO4 by cyclic voltammetry at 80°C. The voltammogram of a Pt electrode cycled between 0.6 and 1.6V vs SCE exhibits an anodic current peak at about 1.3V vs SCE resulting in the deposition of MnO2 on the electrode, while a cathodic peak appears at 0.8V vs SCE. It is shown that the pair of peaks do not correspond to a single reversible reaction but represent two separate irreversible electrode processes. The cyclic voltammetric peak current for the deposition of EMD is found to be proportional to the square root of Mn2+ ion concentration in the electrolyte and independent of acid concentration. Based on these results, a mechanism for the formation of EMD involving diffusion of Mn2+ ions to the electrode surface, oxidation of Mn2+surface to Mn3+ads, and H2O to OHads as the primary oxidation steps is invoked. Mn3+ads ions dissociate disproportionately into Mn2+ads and Mn4+ads ions at the electrode surface. The Mn2+ads and Mn4+ads ions, respectively, react with OHads and H2O resulting in the formation of EMD.

133 citations


Journal ArticleDOI
TL;DR: The application of rotating cylinder electrodes (RCEs) in electrochemistry has been reviewed for the period 1982-1995 as discussed by the authors, highlighting the novel design of cell geometries and reactors for a range of electrochemical processes, voltammetry and analysis, electrodeposition and corrosion.
Abstract: The application of rotating cylinder electrodes (RCEs) in electrochemistry has been reviewed for the period 1982–1995. Among the applications highlighted are the novel design of cell geometries and reactors for a range of electrochemical processes, voltammetry and analysis, electrodeposition and corrosion. This range amply indicates the widespread acceptance of the RCE for studies in a number of interdisciplinary fields.

130 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of plating variables on the composition and morphology of the deposits obtained on vitreous carbon electrodes was investigated, and the results suggest the following sequence of events: first, nickel is deposited; then, cobalt(ii) adsorbs onto the freshly deposited nickel and begins to be deposited.
Abstract: Cobalt–nickel alloys were electrodeposited in an acid bath containing various ratios of metallic cations. The effect of the plating variables on the composition and morphology of the deposits obtained on vitreous carbon electrodes was investigated. Different proportions of the two metals can be obtained by using different deposition parameters, but at all Co(ii)/Ni(ii) ratios studied, preferential deposition of cobalt occurs and anomalous codeposition takes place. For a fixed solution composition, the nickel content in the deposit is enhanced by increasing the deposition potential. More homogeneous and fine-grained deposits can be obtained by increasing the cobalt(ii)/nickel(ii) ratio in solution and by ensuring that deposition takes place slowly. Deposits of constant composition throughout the depth of the deposit can be obtained only by stirring the solution during the deposition. In addition, the solution must be stirred in order to minimize the increase in local pH and to prevent hydroxide precipitation. An attempt was made to explain the anomalous codeposition. The results suggest the following sequence of events: first, nickel is deposited; then, cobalt(ii) adsorbs onto the freshly deposited nickel and begins to be deposited. The cobalt(ii) adsorption inhibits subsequent deposition of nickel, although it does not block it completely.

119 citations


Journal ArticleDOI
TL;DR: In this paper, the performance of a direct methanol fuel cell based on a Nafion® solid polymer electrolyte membrane (SPE) was reported, which utilizes a vaporized aqueous methanoline fuel at a porous Pt-Ru-carbon catalyst anode.
Abstract: The performance of a direct methanol fuel cell based on a Nafion® solid polymer electrolyte membrane (SPE) is reported. The fuel cell utilizes a vaporized aqueous methanol fuel at a porous Pt–Ru–carbon catalyst anode. The effect of oxygen pressure, methanol/water vapour temperature and methanol concentration on the cell voltage and power output is described. A problem with the operation of the fuel cell with Nafion® proton conducting membranes is that of methanol crossover from the anode to the cathode through the polymer membrane. This causes a mixed potential at the cathode, can result in cathode flooding and represents a loss in fuel efficiency. To evaluate cell performance mathematical models are developed to predict the cell voltage, current density response of the fuel cell.

118 citations


Journal ArticleDOI
TL;DR: In this article, the principles of cathodic protection for atmospherically exposed concrete structures, the various protecting effects induced by the cathodic polarization and tests and field experience results are discussed.
Abstract: The paper deals with the principles of cathodic protection for atmospherically exposed concrete structures, the various protecting effects induced by the cathodic polarization and tests and field experience results. The differences between the cathodic protection applied for controlling the corrosion rate of chloride contaminated co nstructions and that applied to improve the corrosion resistance of the reinforcement of new structures expected to become contaminated are then underlined and discussed. The more recent applications of cathodic protection on carbonated concrete are also illustrated. The operating conditions (voltage and current applied), the throwing power, the protection conditions which avoid the risk of hydrogen embrittlement in prestressed structures are also discussed. Examples of cathodic protection and of cathodic prevention are also presented.

Journal ArticleDOI
TL;DR: In this paper, carbon supported iron tetramethoxyphenylporphyrin (FeTMPP) was used as catalysts for the electroreduction of oxygen in direct methanol polybenzimidazole (PBI) polymer electrolyte fuel cells that were operated at 150°C.
Abstract: Carbon supported iron (III) tetramethoxyphenylporphyrin (FeTMPP) heat treated at 800°C under argon atmosphere was used as catalysts for the electroreduction of oxygen in direct methanol polybenzimidazole (PBI) polymer electrolyte fuel cells that were operated at 150°C. The electrode structure was optimized in terms of the composition of PTFE, polymer electrolyte and carbon-supported FeTMPP catalyst loading. The effect of methanol permeation from anode to cathode on performance of the FeTMPP electrodes was examined using spectroscopic techniques, such as on line mass spectroscopy (MS), on line Fourier transform infrared (FTIR) spectroscopy and conventional polarization curve measurements under fuel cell operating condition. The results show that carbon supported FeTMPP heat treated at 800°C is methanol tolerant and active catalyst for the oxygen reduction in a direct methanol PBI fuel cell. The best cathode performance under optimal condition corresponded to a potent ial reached of 0.6V vs RHE at a current density of 900 mAcm−2.

Journal ArticleDOI
TL;DR: In this article, the preparation of cobalt oxides through anodic deposition from Co(NO3)2 aqueous solutions on different substrates is discussed, and the electroformed oxide films exhibit good chemical stability and lower oxygen overvoltages.
Abstract: This paper concerns the preparation of cobalt oxides through anodic deposition from Co(NO3)2 aqueous solutions on different substrates. The electroformed oxide films exhibit good chemical stability and lower oxygen overvoltages, irrespective of the substrate material. Electrocatalytic properties are investigated through polarisation curves and impedance measurements, while the active surface area is estimated by cyclic voltammetry. Experimental data are analysed in terms of a possible reaction mechanism.

Journal ArticleDOI
TL;DR: In this paper, a paste of the catalytic material in Nafion® is coated on a rotating ring disc electrode (RRDE) to partially simulate the working environment of a PEM/electrode composite as used in, for example, water electrolysis or PEM fuel cell operation.
Abstract: A new method for electrochemical characterization of composite electrode materials is reported. A paste of the catalytic material in Nafion® is coated on a rotating ring disc electrode (RRDE) to partially simulate the working environment of a proton exchange membrane (PEM)/electrode composite as used in, for example, water electrolysis or PEM fuel cell operation. This allows direct comparison of a wide range of candidate electrocatalysts in a reproducible manner. Problems specific to these volumic electrodes are accommodated satisfactorily by rational modification of the standard expressions used in RRDE analysis. The value of the method is illustrated in studies of various cobalt complexes which show promise in dioxygen reduction; namely, cobalt tetramethoxyphenylporphyrin (CoTMPP), cobalt phthalocyanine (CoPC), and cobalt cyclam (CoCy), supported on a range of particulate carbons BP2000, Printex XE 2 and Vulcan XC-72. Typical electrochemical parameters have been measured or estimated, including half-wave potentials (E1/2), Tafel slopes (b), ‘activation currents’ (Ia) and the average number of electrons transferred (n). The nature of the complex itself and the carbon support have a strong influence on electrode behaviour. Ligands with more aromatic character give better performance. Dramatic improvements in performance result from heat pretreatment, which is tentatively attributed to the formation of dimeric cobalt species via thermally-induced aggregation. In terms of the four electron reduction (to water), the best result was obtained for CoTMPP on Printex XE2 and rationalized on the basis of popular current views on the mechanism and catalyst functionality. CoPC on BP2000 is unusual in showing a strong change in n with reduction potential. Product selectivity ranges between mainly hydrogen peroxide (n=2) and water (n=4) with increasing overpotential.

Journal ArticleDOI
TL;DR: In this paper, the potential of electroadsorption/desorption on activated carbon for waste water treatment of industrial effluents is studied and two cell designs for the performance of potential controlled adsorption and desorption cycles on the large scale are discussed.
Abstract: The potential of electroadsorption/desorption on activated carbon for waste water treatment of industrial effluents is studied. Adsorption isotherms of hydrophobic differently charged model substances on activated carbon were measured in order to obtain specific information about the influence of the charge (+1,−1 and 0) on the adsorbability of comparable, aromatic species and the influence of the bed potential on the adsorption equilibria. In all these cases the adsorption equilibria show a dependence on applied potential in electrolyte of approximately 1m ionic strength. With electrosorption from aqueous solution, a fivefold enhancement of the concentration in one potential controlled adsorption/desorption cycle is achievable. The use of the solvent methanol instead of water for desorption allows for a concentration enhancement by a factor of hundred in the desorptive step. The adsorption capacity of the activated carbon changes only slightly with cycle number. Two cell designs for the performance of potential controlled adsorption/desorption cycles on the large scale are discussed.

Journal ArticleDOI
TL;DR: In this article, an anode of the type Metal/Ta/Ta2O5-IrO2 with a surface load of 22gm-2 IrO2, submitted to the severe test conditions used in this work, exhibits a standardized lifetime tenfold greater than one made with ASTM grade 4 titanium base metal.
Abstract: Among the numerous base metals tested for DSA® type electrodes (e.g., titanium and its alloys, zirconium, niobium etc.), tantalum is a potentially excellent substrate owing to its good electrical conductivity and corrosion resistance, and the favourable dielectric properties of its oxide. Nevertheless, a DSA® type electrode fabricated on a tantalum substrate would be very expensive due to the high cost of the metal. To prepare an anode combining the excellent properties of tantalum at reasonable price, a new material has been developed in our laboratory. This consists of a common base metal (e.g., Cu) covered with a thin tantalum coating. This tantalum layer was obtained by molten salt electroplating in a LiF–NaF–K2TaF7 melt at 800°C. Thus, an anode of the type Metal/Ta/Ta2O5–IrO2 with a surface load of 22gm-2 IrO2, submitted to the severe test conditions used in this work, exhibits a standardized lifetime tenfold greater than one made with ASTM grade 4 titanium base metal. Thus, this type of electrode might be advantageously employed as an oxygen evolution anode in acidic solutions.

Journal ArticleDOI
TL;DR: In this paper, heat-treated μ-oxo-iron, tetramethoxy phenyl porphyrin (Fe-TMPP)2O and iron(iii) tetramerethoxy porphrin (FeOEP-Cl) adsorbed on high-area carbons such as deashed and un-deashed RB carbon (Calgon) and Black Pearls-2000 (Cabot) have been found to exhibit stable and very high oxygen reduction rates.
Abstract: Heat-treated μ-oxo-iron(iii) tetramethoxy phenyl porphyrin (Fe-TMPP)2O and iron(iii) tetramethoxy phenyl porphyrin (FeTMPP-Cl) as well as iron(iii) octaethyl porphyrin (FeOEP-Cl) adsorbed on high-area carbons such as deashed and un-deashed RB carbon (Calgon) and Black Pearls-2000 (Cabot) have been found to exhibit stable and very high oxygen reduction rates. Experiments done over a period of 24h showed no performance degradation. Measured performances were very similar to supported platinum (E-Tek), when tested in 85% H3PO4-equilibrated Nafion 117 membrane at 125°C and hydrated-Nafion membrane at 60°C in a minifuel cell. The macrocycle cathodes are insensitive to the presence of methanol whereas the platinum cathodes are very sensitive and show degradation in the oxygen reduction performance.

Journal ArticleDOI
TL;DR: In this paper, a small scale Liquid Feed Direct Methanol Fuel Cell (LFDMFC) based on solid polymer electrolyte membrane is reported, where two flow cell designs, one with a parallel flow channel arrangement and the other with a spot design of flow bed, are used.
Abstract: A study of a small scale Liquid Feed Direct Methanol Fuel Cell (LFDMFC), based on solid polymer electrolyte membrane, is reported. Two flow cell designs, one with a parallel flow channel arrangement and the other with a spot design of flow bed, are used. The structure of the DMFC comprises a composite of two porous electrocatalytic electrodes; Pt–Ru–carbon catalyst anode and Pt–carbon catalyst cathode, on either side of a solid polymer electrolyte (SPE) membrane. The performance of three Pt–Ru catalysts is compared. The influence of the degree of Teflon loading on the electrode structure is also reported. The effect of the following parameters: cell temperature, oxygen gas or air pressure, methanol liquid flow rate and methanol concentration on the power performance is described.

Journal ArticleDOI
TL;DR: In this article, the threshold electrode potential for oxygen evolution increased with an increase in the TiO2 content more remarkably than that for chlorine evolution, while the chlorine evolution potential was unchanged.
Abstract: Chlorine and oxygen evolving at RuO2/Ti and RuO2–TiO2/Ti anodes have been simultaneously determined at electrode potentials from 1.0 to about 2V (vs Ag/AgCl) by differential electrochemical mass spectroscopy (DEMS). On the RuO2/Ti anodes, the threshold electrode potential for oxygen evolution increased with a decrease in RuO2 loading, while the chlorine evolution potential was unchanged. Low RuO2 loading anodes gave a high chlorine evolution ratio under various constant electrolysis potentials. On the RuO2–TiO2/Ti anodes, the threshold electrode potential for oxygen evolution increased with an increase in the TiO2 content more remarkably than that for chlorine evolution. High TiO2 content anodes gave a high chlorine evolution ratio at various constant electrolysis potentials. The combination of RuO2 and TiO2 exhibits a remarkable effect with respect to the enhancement of chlorine evolution selectivity.

Journal ArticleDOI
TL;DR: In this article, the performance of tin dioxide electrodes with antimony and platinum was investigated by cyclic voltammetry in sulphuric acid using the Fe2+/Fe3+ redox couple system as test reaction.
Abstract: Doped tin dioxide electrodes have been prepared by a standard spray pyrolysis technique. The electrochemical behaviour of these electrodes has been investigated by cyclic voltammetry in sulphuric acid using the Fe2+/Fe3+ redox couple system as test reaction. Oxygen evolution has been used to study the stability of doped SnO2 electrodes. The SnO2 electrodes doped with antimony and platinum exhibit the highest stability. XPS analysis shows that the oxidation state of Sn, Sb and Pt are +4, +3 and +2, respectively, the probable species being SnO2, Sb2O3 and PtO.

Journal ArticleDOI
TL;DR: In this paper, RuO2-doped Co3O4 electrodes were prepared by thermal decomposition of the corresponding nitrates using Ni as a support, and the RuO 2 content was varied between 0 and 20mol%.
Abstract: RuO2-doped Co3O4 electrodes were prepared by thermal decomposition of the corresponding nitrates using Ni as a support. The RuO2 content was varied between 0 and 20mol%. The kinetics of hydrogen evolution from alkaline solution was studied by recording quasisteady state polarization curves at several NaOH concentrations. A mechanism is proposed on the basis of Tafel slopes and reaction orders. The electrocatalytic activity of the mixed oxides has been found to go through a maximum at intermediate RuO2 contents. Some evidence of instability has emerged.

Journal ArticleDOI
TL;DR: LiCoO2 has been synthesized by a solid-state synthesis route involving the decomposition and intercalation of hydroxide precursors generated by precipitation and freeze-drying as discussed by the authors.
Abstract: LiCoO2 has been synthesized by a solid-state synthesis route involving the decomposition and intercalation of hydroxide precursors generated by precipitation and freeze-drying. Cyclic voltammetry of LiCoO2 obtained by heating at 100°C for 2h has shown this material to be electrochemically active with an initial discharge capacity of 92mAhg−1. Optimization of processing conditions reduced the firing time to as little as 2h at 800°C, producing LiCoO2 powders with high reversible capacity (142mAhg−1), good rate capability, and good cyclability. The favourable performance of this oxide powder in LiCoO2/C lithium-ion cells using the present oxide powders shows the instant synthesis route to be promising and cost-effective for lithium-ion battery applications.

Journal ArticleDOI
TL;DR: In this article, a quaternary metal oxide film was applied to the anode of a Ti or Pt anode for the electrochemical incineration of p-benzoquinone.
Abstract: Electrochemical incineration of p-benzoquinone was evaluated as a model for the mineralization of carbon in toxic aromatic compounds. A Ti or Pt anode was coated with a film of the oxides of Ti, Ru, Sn and Sb. This quaternary metal oxide film was stable; elemental analysis of the electrolysed solution indicated the concentration of these metal ions to be 3μg L−1 or less. The anode showed good reactivity for the electrochemical incineration of benzoquinone. The use of a dissolved salt matrix as the so-called ‘supporting electrolyte’ was eliminated in favor of a solid-state electrolyte sandwiched between the anode and cathode. This substitution permitted the electrolysis solution to be analysed by electrospray mass spectrometry (ESMS); however, as a consequence, electrolysis periods were excessively long. Total organic carbon (TOC) and chemical oxygen demand (COD) decreased to 1–2 mgL−1 after 64h of electrolysis. The solution pH changed from 5 to 4. Phenolic and carboxylic acid intermediate products such as hydroquinone, maleic acid, fumaric acid, succinic acid, malonic acid, acetic acid and formic acids were identified and quantified using solid phase microextraction with gas chromatography with mass spectrometric detection (GCMS) or liquid chromatography (LC) with conductivity detection, absorbance detection, or electrosprary mass spectrometry (ESMS). Less than 1% of the carbon in benzoquinone was converted to acetone and acetaldehyde.

Journal ArticleDOI
TL;DR: In this article, the Pt-PEM electrodes were characterized by TEM, atomic absorption analysis, cyclic voltammetry and their polarization curves for ethanol electrooxidation and the platinization procedure was modified to enhance the roughness factor and thus to improve the electrocatalytic activity towards ethanol electrooxide.
Abstract: Nafion® can be used as a solid polymer electrolyte in a PEM fuel cell. Direct platinization of the membrane was realized by chemical reduction of a platinum compound. The platinization procedure was modified to enhance the roughness factor and thus to improve the electrocatalytic activity towards ethanol electrooxidation. The Pt–PEM electrodes were characterized by TEM, atomic absorption analysis, cyclic voltammetry and their polarization curves for ethanol electrooxidation.

Journal ArticleDOI
TL;DR: In this article, the surface phenomena occurring on the polymer during this initiation time are studied through the chemical form of palladium adsorbed on the surface and through changes in the Pd surface concentration.
Abstract: This paper deals with polymer metallization by the electroless process. Previous studies in the authors' laboratory have shown the interest of plasma surface treatments of polymers before chemical metallization and the significant role they play towards the chemisorption of a catalyst (Pd2+ ions). Three different processes are used to activate the polymer surface for electroless deposition: namely, the one-step process using a mixed SnCl2–PdCl2 solution, the conventional two-step process using SnCl2, then PdCl2, and a new simplified process (using only PdCl2), previously proposed by the authors. According to the process utilized a variable initiation time is observed before metal deposition takes place in the metallization bath. The surface phenomena occurring on the polymer during this initiation time are studied by XPS through the chemical form of palladium adsorbed on the surface and through changes in the Pd surface concentration. A reaction mechanism relative to the initiation of the metallic ion reduction is proposed.

Journal ArticleDOI
TL;DR: In this paper, the authors used an argon sputter gas and a V 2 O 5 target to synthesize amorphous V2 O 5 films, which were characterized by scanning electron microscopy, atomic force microscopy and X-ray diffraction.
Abstract: Vanadium oxide films were prepared by r.f.-sputtering using an argon sputter gas and a V 2 O 5 target. The films were characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical techniques. The oxide film as deposited is amorphous; they are heat-treated in the range 300-700 °C in oxygen atmosphere and are composed of orthorhombic V 2 O 5 crystals. At higher heat-treatment temperatures (600-700°C) the crystallization of the oxide proceeded significantly with ab-direction parallel to the substrate. The oxide film undergoes a reversible lithium intercalation and deintercalation process. The kinetics of the intercalation process of lithium into amorphous V 2 O 5 film was studied using an a.c. impedance method. Furthermore, a rocking-chair type V 2 O 5 film/Li x V 2 O 5 film cell could be charge-discharge cycled over 300 times at a current of 10 μA at 25 °C.

Journal ArticleDOI
TL;DR: In this article, a rotating disc electrode in an argon-deaerated solution in the temperature range 20 to 50°C was studied using electrochemical impedance spectroscopy and quasi steady-state polarization.
Abstract: Corrosion kinetics of 99.6% aluminium covered by a thin spontaneously formed oxide film in hydrochloric acid solution with and without the presence of substituted N-aryl pyrroles was studied using electrochemical impedance spectroscopy and quasi steady-state polarization. Measurements were performed on a rotating disc electrode in an argon-deaerated solution in the temperature range 20 to 50°C. The addition of inhibitor considerably increases overvoltage of the cathodic process (HER) and shifts Ecorr to negative potential values. The activation energy of the hydrogen evolution reaction was Ea=50±5kJmol−1 and was not affected by the presence of inhibitor. The inhibitory action occurs by π-bonding between the adsorbed inhibitor molecules and the electrode surface. The electrode coverage follows the Langmuir adsorption isotherm with an adsorption equilibrium constant K=1.1–2.64×105dm3mol−1. The adsorption of organic compound prevents the adsorption of chloride ions and slow down the rate of corrosion.

Journal ArticleDOI
TL;DR: In this paper, the dielectric properties of oxide films were investigated in the following electrolytes: H2SO4, HNO3, H3PO4 and NaOH.
Abstract: The electrochemical oxidation of Ta and Nb and the dielectric behaviour of the oxide films thus formed were investigated in the following electrolytes: H2SO4, HNO3, H3PO4 and NaOH. Characterization of the films was carried out by means of potentiodynamic current–potential profiles (in the range 0–8V) and electrochemical impedance spectra (in the range 0.1Hz–100kHz). The a.c. response of the oxide films was modelled as a single layer structure on the basis of an equivalent circuit with constant phase elements (CPE). The dependence of the oxide resistance and oxide capacitance with potential is also reported.

Journal ArticleDOI
TL;DR: In this paper, the electrochemical behavior of massive chalcopyrite electrodes has been studied in an acid medium (pH1.5) containing silver ions (0.02gdm−3Ag+) and thermophilic bacteria (68°C).
Abstract: The electrochemical behaviour of massive chalcopyrite electrodes has been studied in an acid medium (pH1.5) containing silver ions (0.02gdm−3Ag+) and thermophilic bacteria (68°C). Preliminary tests on particulate electrodes made from graphite, elemental sulfur and Ag2S were included to determine the electrochemical response of reactants (Ag+) and products (S° and Ag2S) associated with the dissolution of chalcopyrite in the presence of silver. Massive chalcopyrite electrodes under potential scan showed a dependence on the dissolution of the Ag2S film with both the time of contact with the silver solution and [Ag+]. As well as Ag2S, metallic silver was detected on the chalcopyrite surface. It has been demonstrated that Fe3+ and bacteria play an important role in the regeneration of the Ag2S film. The breakdown of this film is a requirement for the further dissolution of chalcopyrite. The bioleaching of chalcopyrite with thermophilic microorganisms in the presence of silver decreased the decomposition potential of the electrode and favoured its electrodissolution. Bioleaching treatment in the presence of silver ions for periods of time longer than two weeks did not improve the surface reactivity. However, in the initial stages of the process, the lower reactivity of the bioleached electrodes was probably related to a toxic effect of silver on the microorganisms.

Journal ArticleDOI
TL;DR: In this article, a voltage-step transient experiment is used to calibrate electrodiffusion (ED) friction probes in high-speed rotating impellers and the results show that shear rates as high as 106s-1 can be reliably measured using 0.5mm Pt working electrodes in ferro/ferricyanide aqueous solutions.
Abstract: Voltage-step transient experiments are used to calibrate electrodiffusion (ED) friction probes. The approach is demonstrated on the probes in high-speed rotating impellers. This calibration has shown that shear rates as high as 106s-1 can be measured reliably using 0.5mm Pt working electrodes in ferro/ferricyanide aqueous solutions. The complete transient calibration experiment provides sufficient information about the dynamics of ED friction probes.