Linear Sweep Voltammetry Measurements Research Articles

Effect of heat treatment on the anodic oxidation of Ti–0.2 Pd alloys in chloride solutions

The effect of heat treatment of Ti and Ti–0.2 Pd alloys on their anodic oxidation was studied in deaerated 1% NaCl by means of anodic linear sweep voltammetry, SEM, TEM, EDS, optical microscopy and microhardness measurements. The specimens, as fabricated, consisted of α-phase only. The β-phase, intergranular or with a Widmansttaten type growth, was produced by heat treatment of the Ti–0.2 Pd alloys at the temperature range from 750 to 850 ∘C. The β-phase was transformed into the α′-phase during quenching. The current density against voltage curves for pure Ti and Ti–0.2 Pd, as fabricated or heat-treated, presented an initial plateau at about 1.5 V vs Ag/AgCl/KCl (3 M), an anodic peak at about 4.5 V and a current increase due to the pitting attack at about 10 V. The anodic peak was related to an oxide growth together with a solution electrolysis. Current spikes appeared at random from potentials about 8.3 V, which were related to film breakdown and repair events. The passive films of the alloys oxidized up to about 10 V presented oxidation bands parallel to the surface, with different oxygen content and microhardness, together with a structural transformation of the α′-phase under the titanium oxide layer. The similar behaviour of pure Ti and Ti–0.2 Pd alloys in front of pitting corrosion in chloride was due to such a structural transformation.

Kinetics of O 2 Reduction on a Pt Electrode Covered with a Thin Film of Solid Polymer Electrolyte

The kinetics of reduction on both oxidized and reduced Pt rotating disk surfaces covered with thin films (1 to 15 μm) of recast polybenzimidazole (PBI) or Nafion have been examined in 0.1 M aqueous solutions of , and at 25.0°C. Polymer films were deposited on a Pt disk electrode by a spin‐coating technique. Experiments were performed at different rotation rates and potential scan rates. This investigation was undertaken to establish to what extent the solid polymer electrolyte influences the mechanism and kinetics of reduction. The number of electrons exchanged per molecule and kinetic parameters for reduction (reaction order with respect to , Tafel slope/transfer coefficient, and exchange current density) are not changed in the presence of the polymer films, indicating that the reaction path and kinetics are not altered in the presence of recast PBI and Nafion films. The diffusion coefficient (D) and concentration (C) of in recast films were determined by means of linear sweep voltammetry measurements in quiescent solution. The D and C values in polymer films immersed in acidic solutions were found to have different values than those in the solutions. is about 2.5 times lower in the recast films than in the solutions, whereas is slightly higher in the film. The largest concentration increase, by a factor of two, was found in PBI film in 0.1 M . Cyclic voltammetric measurements under argon atmosphere have shown that PBI and Nafion recast films are electrochemically stable in the potential range between the onsets of and evolution. A decrease in the effective electrocatalyst surface area due to deposition of solid polymer films was 15 to 20%.

A Stable Thin‐Film Lithium Electrolyte: Lithium Phosphorus Oxynitride

The electrochemical and optical properties of lithium phosphorous oxynitride (Lipon) thin films have been studied with an emphasis on the stability window vs. lithium metal and the behavior of the Li/Lipon interface. Impedance measurements made between −26 and 140°C show that Lipon exhibits a single, ‐ion conducting phase with an average conductivity of 2.3 (±0.7) × 10−6 S/cm at 25°C and an average activation energy of . No detectable reaction or degradation was evident at the Li/Lipon interface, and linear sweep voltammetry measurements on three‐electrode cells indicated that Lipon is stable from 0 to about 5.5 V with respect to a /Li reference. The complex refractive index of Lipon was measured by spectroscopic ellipsometry. Optical bandgaps of 3.45 and 3.75 eV were obtained from the ellipsometry data and from optical absorption measurements, respectively.

Kinetics of chloride ion adsorption and the mechanism of AgCl layer formation on the (111), (100) and (110) faces of silver

The kinetics of chloride anion adsorption on the (111), (100) and (110) faces of silver are investigated by linear sweep voltammetry, potentiostatic pulse and impedance (admittance) measurements. It is shown that the first voltammetric (capacitive) peak corresponds to the adsorption of randomly arranged chloride anions with complete charge transfer between the anions and the substrate ( l ≈ 1) and a relatively slow rate of adsorption: k s = (8−9) × 10 −6 cm s −1. The second (third) voltammetric (capacitive) peak is found to be very sharp, representing (according to the earlier findings) the formation of an ordered AgCl adlayer formed with the topmost Ag layer. At more positive potentials a three-dimensional (3D) growth of AgCl takes place, characterized by the anodic “crystallization loop” and the j− t transients typical of 3D nucleation. It is shown that after prolonged polarization in the potential region of 3D AgCl formation, irreversible formation of AgCl takes place on the electrode surface.

Improvement of the performance of the positive electrode in the lead/acid battery by addition of boric acid

A major disadvantage of the lead/acid battery is the decrease in voltage during operation which makes it unsuitable for systems sensitive to voltage fluctuations. Additives like BaSO 4 or SrSO 4, which are isomorphous to PbSO 4, have been used to overcome this problem. Phosphoric acid and the various phosphates have long been used to improve the performance of the positive electrode of the battery. A beneficial effect of phosphoric acid is to inhibit the rate of the self-discharge reaction of the positive electrode in the lead/acid battery. However, adverse effects of phosphoric acid include capacity loss in the initial cycles, excessive mossing, especially at high H 3PO 4 concentrations, and poor low-temperature performance (decrease in the rate of PbSO 4 oxidation). The effect of boric acid as an additive substituting for H 3PO 4 has been investigated using linear sweep voltammetry, constant potential and impedance measurements. The results show that boric acid markedly improves the kinetics of the PbO 2 PbSO 4 couple and removes the problems encountered during the usage of H 3PO 4.

Anodic oxidation of antimony at high overpotentials — formation of a barrier layer and klebelsbergite

The anodic oxidation of antimony at potentials higher than 0.0 V (vs. Hg/Hg 2SO 4/K 2SO 4) in strong acid solutions was investigated using linear sweep voltammetry, potentiostatic polarization, photo-voltammetry and ac impedance measurements. The anodic layer structure was observed by scanning electron microscopy and its phase composition determined by X-ray diffraction. At potentials higher than 0.0 V, after a certain quantity of charge has passed through the electrode, an anodic multilayer is formed. It comprises a barrier layer at the metal side, a basic sulphate gel-like layer at the solution side and a hydroxide layer in between. The growth of the barrier layer is determined by a high-field assisted ion migration. This layer has semiconductor properties and a band gap of 2.2±0.1 eV. Its formation is essential in order to reach appropriate conditions for the nucleation of klebelsbergite (Sb 4O 4 (OH) 2SO 4) which is stable in H 2SO 4 solutions.

Equilibrium potentials at the polymer-water interface

From emf, impedance and linear sweep voltammetry measurements, equilibrium potentials at the interface between aqueous solutions and PVC-based plasticized (with di-octyl sebacate or o-nitrophenyl octyl ether) membranes have been determined for the ionic species AsPh + 4, NMe + 4, NEt + 4, BPh − 4, K + and Ca 2+. In the last two cases ionophores were present in the membrane, valinomycin for K + and ETH129 for Ca 2+. A voltammetric wave has been found for the transfer of NEt + 4 from the water to the membrane phase. From the partition coefficient of AsPh 4BPh 4 between the two phases, the free energies of transfer have been evaluated.

The influence of solution composition on lead, cadmium and thallium underpotential deposition on (111) oriented silver single crystal surfaces

The influence of solution composition on the process of lead, cadmium and thallium UPD on (111) oriented silver single crystal surfaces has been investigated by using linear sweep voltammetry and differential capacity measurements. It is shown that the Y'-E curves can be used qualitatively as a criterion for the occurrence of partial charge transfer reactions in the double layer region and the commencement of the faradaic reaction of UPD. The C-E curves obtained in the presence and in the absence of depositing metal cations can give useful information about the nature of species present in the solution and adsorbed onto the substrate surface. It is also demonstrated that the presence of different complexes of cations investigated and the kinetics of their reduction can be responsible for a change in the UPD voltammograms.

On the electrochemistry of dissolved aluminium in cryolitic melts

The electrochemical oxidation of dissolved aluminium was studied in alumina saturated cryolitic melts at 1000°C by linear sweep voltammetry and chronopotentiometric measurements. The oxidation reaction was found to be diffusion controlled and the overall diffusion coefficient of dissolved aluminium ( D Al) in alumina saturated cryolite was; ▪ The transport number due to partly trapped electrons ( t e ) was by the use of literature data from studies on the migration velocity of dissolved aluminium and on the solubility of aluminium, estimated to be very low in cryolitic melts at 970°C ( t e < 0.5%).

Electrochemical investigations on the behaviour of thallous ions during the formation of PbSO 4

The influence of thallous ions Tl(I) on the charge-discharge process of a stationary lead electrode has been investigated in sulphuric acid solution at ambient and sub-zero temperatures. Linear sweep voltammetry and potential step measurements were employed to examine the process of nucleation and growth of lead sulphate crystals. The initial oxidation reaction kinetics were found to be controlled by three-dimensional growth under diffusion control. The presence of thallous ions affected the morphology of lead sulphate crystals, increased the amount of charge required for passivation and decreased the rate of the discharge process.

The cathodic reduction of PbO in the passive layer on lead in aqueous sulphuric acid

The cathodic reduction of the lead monoxide layer formed on lead in 30% aqueous H2SO4 under anodic oxidation at 0.6 V (vs. Hg/HgSO4 reference electrode) was investigated by linear sweep voltammetry, potential step and admittance measurements. The experimental data were analyzed respectively in terms of thin-layer electrochemistry, electrocrystallisation, and changes of resistance of the PbO layer under reduction. The results seem to be best interpreted from the theory of three-dimensional electrocrystallisation as PbO is reduced to Pb. At sub-zero temperatures the PbO peak observed on our voltammograms and potentiostatic current time transients reveals the splitting of the curves into two peaks, which may be a result of reduction of the same material but of different phases, namely, orthorhombic and tetragonal PbO.

Instability of Anodic Oxide Films on Titanium

Linear sweep voltammetry, photocurrent spectroscopy, impedance and reflectance measurements have been used to study the growth and stability of anodic oxide films on titanium in and . Films were grown typically to a formation voltage of 40V (∼100 nm) and had a density close to that of anatase, 3.9 g cm−3. Two regimes of oxide film instability have been identified. The first occurs during growth and is manifested by a reduction in growth current efficiency preceded by unusual photocurrent and impedance behavior. The second, which occurs when the field is reduced, appears as a sharp current spike accompanied by film thickening and sudden changes in the impedance and photocurrent conversion efficiency. A link between the two phenomena is established and the dependence on growth rate and formation voltage discussed. A model based on the formation of a damaged surface layer covering a fresh barrier layer is presented.

Improvements in linear sweep voltammetry measurement precision Half peak potential and linear current potential correlation

Improvements in linear sweep voltammetry measurement precision Half peak potential and linear current potential correlation

Improvements in linear sweep voltammetry measurement precision: Half peak potential and linear current potential correlation

Improvements in linear sweep voltammetry measurement precision: Half peak potential and linear current potential correlation

A study of the electrochemical characteristics of some thiols by differential pulse polarography and other electrochemical techniques

A study of some low-molecular-weight odorous thiols at mercury electrodes has been made by differential pulse polarography (d.p.p.), d.c. polarography, linear-sweep voltammetry, and coulometric measurement on linear-sweep reduction. Linear current versus concentration plots are found for individual thiols, in aqueous 0.2 M sodium hydroxide by using d.p.p. at thiol concentrations from ca. 2 × 10 -7 M to 10 -4 M. A linear trend between peak potential and molecular weight was found for homologous series, but the method cannot be used for qualitative identification because of peak shifts in multicomponent mixtures. The electrode reactions show quasireversible behavior. At concentrations of thiol greater than 10 -4 M, the single peak splits into two peaks and film formation occurs. Charge density versus concentration plots indicate that the quantity of adsorbed material is several monolayers.

Anodic oxidation of hydrogen on substoichiometric tungsten trioxides: A study by electron paramagnetic resonance and by linear and cyclic voltammetry

The catalytic activity of the substoichiometric tungsten trioxide electrodes for the oxidation of hydrogen has been investigated, using simultaneous EPR spectroscopy and linear-sweep voltammetry measurements. The parameters of the EPR spectral line observed for all oxides except stoichiometric WO3 were determined in relation to the electronic structure of the paramagnetic centers associated with the oxygen anion vacancies. Hydrogen adsorption was followed by means of changes both in the EPR line parameters and in the electrode potential. The intensity-versus-potential curves for suboxide electrodes under hydrogen were analyzed in terms of the occurrence of two processes. It was shown that one process is associated with the hydrogen oxidation and that the other is connected with oxidation of the WO3−x surface. The mechanisms of both reactions were interpreted as involving the formation and oxidation of an hydrogen tungsten bronze.