Current-potential Characteristics Research Articles

Influence of the reactivity of reducing agents on anodic photocurrents at TiO 2 electrodes

Effects of reducing agents in electrolytes on photocurrent-potential characteristics of TiO 2 electrodes were investigated. It was observed that the reducing agents with a high reactivity caused negative shifts of the onset potential of the photocurrent. The competitive consumption of photogenerated positive holes between surface recombination and charge transfer reactions seems to be responsible for the phenomena observed. The correlation between the current-potential characteristics and the reactivity of the reducing agents are discussed with the use of a simple surface recombination model. It is shown that theoretically derived rate equations using the simple surface recombination model are useful for predicting the current efficiency for competing reactions at the electrode.

The electrolysis of steam using uranium oxide electrodes

The production of hydrogen by the high-temperature electrochemical decomposition of steam was carried out using a cell composed of 70 mol% UO 2.67-30 mol% YO 1.5 electrodes and an yttria-stabilized zirconia electrolyte. The current-potential characteristics at temperatures in the range 1273–1773 K were studied using a galvanostatic technique. The data were found to obey a Tafel relationship, and values of the slope, charge transfer coefficient, and exchange current density at each temperature of interest were derived. The efficiency of the steam-decomposition cell was also determined, and it was shown that this increases with increase of temperature.

Electrochemical behaviour of the oxide covered antimony

The electrochemical behaviour of the system Sb-oxide layer-0.05 M H 2SO 4 was investigated by impedance, photopolarization and by recording voltammetric characteristics in the presence of the redox couple K 3Fe(CN) 6-K 4Fe(CN) 6 from 1.6 to −0.86 V vs mercury mercurous sulphate electrode. Attention has been concentrated on potentiodynamically formed and stabilized films whose thickness enabled the development of the space charge. It will be shown that the mechanism of charge transfer in the Sb-oxide layer-electrolyte system having a given form of current potential characteristics, is dependent on the semiconducting properties of the oxide layer, which can be modified owing to the breaking of bonds and the formation of new ones. Impedance and photoelectric polarization have proved very sensitive and suitable for the investigation of structural and phase change of the solid phase in situ with potential changes in continuous polarization.

酸性くえん酸浴による光沢Ｆｅ‐Ｍｏ合金めっきと電着過程の２，３の性質について

Crack-free iron-molybdenum alloy coating having a micro-vickers hardness of a bout 450 and a light black hue has been electroplated onto mild steel substrates at cathodic current densities of 1-1.5A/dm2 and at 35°C. The optimum electrolyte composition was found to be 0.26mol/l Na3C6H5O7, 0.12mol/l Na2MoO4, and 0.14mol/l of FeSO4 at pH 4.0 adjusted with dilute H2SO4. The alloy composition exactly corresponds to Fe3Mo. Transmission and reflection electron diffraction patterns of the alloy showed an amorphous structure but the surface was found to be crystallized. Three kinds of the alloy plating baths in which sodium or potassium concentration is kept constant at two different levels have been prepared for the analysis of the current-potential characteristics. In addition, the catholyte pH was directly measured by using an antimony microelectrode. It was found that the electrodeposition involves a cycle of electrolytic reduction-reoxidation by the sodium, potassium and molybdenum ions. It was also revealed that sodium and potassium atoms form a layer on the electrode to protect the electrode surface from the reoxidation of electrolytically formed lower oxide of molybdenum. This provides a good explanations for the previously reported characteristics of the induced molybdenum codposition.

A unified theory of streaming maxima of first and third kind, as well as of their suppression

A unified theory of streaming maxima of the first kind (including those due to reactant adsorption) and of the third kind is formulated, together with an interpretation of their suppression by electroinactive surfactants. This theory is based on Frumkin and Levich's [6–8] solution of the equations for the motion of a spherical liquid drop whose interfacial tension is a cosine function of the colatitude ϑ. The electrochemical boundary conditions for this hydrodynamic problem are, however, modified with respect to those adopted by Frumkin and Levich, taking into account that radial convective plus diffusive transport of electroactive and surface-active substances towards the drop surface prevails over radial migrational transport, during the occurrence of polarographic maxima. In this connection a time- and ϑ-dependent expression for the convective plus diffusive flux of a reactant towards a spherical electrode under non-steady-state conditions is derived by two-step Laplace transformation of the corresponding boundary value problem. An approximate solution of the combined hydrodynamic and electrochemical boundary value problem yields theoretical currentpotential characteristics which account satisfactorily for all salient features of both positive and negative maxima of the first kind. In particular, it is shown that streaming is autocatalytic (and hence gives rise to streaming maxima) when a cathodic current flows at a positively charged electrode (or else an anodic current flows at a negatively charged electrode) and when the reactant is more strongly adsorbed (either specifically or non-specifically) than the product. When in the presence of an electroinactive surfactant obeying a Frumkin isotherm with an interaction factor a′ less than −4 (namely undergoing two-dimensional condensation), the theory predicts current-potential characteristics in semiquantitative agreement with experimental maxima of the third kind.

A unified theory of streaming maxima of first and third kind, as well as of their suppression

A unified theory of streaming maxima of the first kind (including those due to reactant adsorption) and of the third kind is formulated, together with an interpretation of their suppression by electroinactive surfactants. This theory is based on Frumkin and Levich's [6–8] solution of the equations for the motion of a spherical liquid drop whose interfacial tension is a cosine function of the colatitude ϑ. The electrochemical boundary conditions for this hydrodynamic problem are, however, modified with respect to those adopted by Frumkin and Levich, taking into account that radial convective plus diffusive transport of electroactive and surface-active substances towards the drop surface prevails over radial migrational transport, during the occurrence of polarographic maxima. In this connection a time- and ϑ-dependent expression for the convective plus diffusive flux of a reactant towards a spherical electrode under non-steady-state conditions is derived by two-step Laplace transformation of the corresponding boundary value problem. An approximate solution of the combined hydrodynamic and electrochemical boundary value problem yields theoretical currentpotential characteristics which account satisfactorily for all salient features of both positive and negative maxima of the first kind. In particular, it is shown that streaming is autocatalytic (and hence gives rise to streaming maxima) when a cathodic current flows at a positively charged electrode (or else an anodic current flows at a negatively charged electrode) and when the reactant is more strongly adsorbed (either specifically or non-specifically) than the product. When in the presence of an electroinactive surfactant obeying a Frumkin isotherm with an interaction factor a′ less than −4 (namely undergoing two-dimensional condensation), the theory predicts current-potential characteristics in semiquantitative agreement with experimental maxima of the third kind.

Electrochemical polarization phenomena at the interface of two immiscible electrolyte solutions

The faradaic and non-faradaic processes taking place at the interface of two immiscible electrolyte solutions have been compared with analogous processes occurring at the interface metal-electrolyte solution. For the former interface conditions have been stated for obtaining suitable current-potential characteristics. As methods of investigation, cyclic voltammetry, chronopotentiometry and polarography with an electrolyte dropping electrode have been used. For the simple ion transfer across the interface, examples of reversible and irreversible processes have been described. In the presence of ionophores (valinomycin and a crown polyether) the transfer of alkali metal ions is facilitated. This phenomenon has been exploited for determination of stability constants. The interface of two immiscible electrolyte solutions may be used as a model of the surface of a biological membrane.

A magnetically shielded sampling technique for plasma diagnostics in a medium-pressure magnetoplasma

A magnetically shielded sampling technique is developed which permits determination of plasma parameters by orifice probe, electrostatic analyser or mass spectrometer for medium-pressure magnetised plasmas. Experimental results show that: for a retarded-electron current no abnormal peak or non-exponential potential dependence of current potential characteristics as observed by previous orifice probe measurements in a magnetised plasma is observed; electron temperature measurements agree to within 10% with recent positive-column electron temperature theory; and plasma density measurements agree to within a factor of 3 with electrostatic probe measurements.

A detailed analysis of the polarographic behaviour of methylene blue in phosphate buffer on mercury

Polarographic current-potential characteristics and current-time curves for the reduction of methylene blue (MB) to methylene blue leucoform (MBL) in a pH 7.9 aqueous phosphate buffer have been examined in detail over a wide concentration range. It has thus been shown that the so called “normal” or “main” reduction wave of MB actually consists of two separate steps, the former with a half-wave potential practically coinciding with the formal potential E 0=−0.250 V/SCE of the MB/MBL couple and the latter with a half-wave potential of about −0.310 V/SCE. As soon as the well-known MB adsorption prewave has attained its maximum height (which occurs at a MB bulk concentration c 0 *⋟5×10 −5 M), a further slight increase in c 0 * causes the appearance of the wave with E 1/2=−0.310 V. The height of the linear potential-sweep voltammetric peak corresponding to the latter wave increases proportionally to the sweep rate, thus revealing the “adsorption” nature of this wave. A comparison with a previous chronocoulometric investigation of the MB/MBL system has permitted us to conclude that the wave with E 1/2=−0.310 V is due to reduction of the MB molecules which, after having reached the surface of the dropping electrode by diffusion, are adsorbed at the top of the adsorbed monolayer of MBL in direct contact with the electrode and remain in this adsorbed state after reduction. For c 0 *>7×10 −5 M the wave with E 1/2⋟ E 0=−0.250 V starts to develop. This wave is due to the electroformation of MBL molecules which diffuse back into the solution. The shape of polarographic current-potential characteristics and current-time curves has been accounted for semiquantitatively through an approximate solution of the corresponding diffusional problem.

Mathematical treatment of polarographic reversible adsorption waves and considerations on their origin

Polarographic current-potential characteristics and current-time curves for a Nernstian charge transfer O+ neR with Langmuir or Frumkin adsorption of reactant and/or product are derived via a mathematical procedure based on the diffusion-layer approximation. It is shown that all features of reversible adsorption waves can be explained by the effect of adsorption of reactant and product upon the only rate-determining stage, namely the diffusion stage. Conversely, no conclusion can be drawn as to whether charge transfer takes place in the adsorbed or else in the non-adsorbed state from a comparison between theoretical predictions and experimental behaviour. The origin of adsorption prewaves and post-waves is justified by the concept of entropy production, which can also be used to explain the origin of the so-called adsorption pseudo-prewaves.

ChemInform Abstract: NOVEL SEMICONDUCTING ELECTRODES FOR THE PHOTOSENSITIZED ELECTROLYSIS OF WATER

AbstractDurch Aufsprühen entsprechender Elementchlorid‐Lösungen auf ein Ti‐Substrat und thermische Zersetzung der Chloride werden TiO2‐Alzüa‐ , TiO,‐SrO‐, TiOg ‐ Ga,O3‐, TiO,‐Eu,O3‐ und TiO2 ‐B,O3‐Elektroden hergestellt und ihre Eigenschaften bei der Verwendung als Photoanoden für die Wasserelektrolyse untersucht.

Study of the Injection Type IPOS Scheme

A new method, called the injection type IPOS, which consists of anodization of a n-type layer by injection of holes from a p-type substrate and oxidation, is reported. Formation of porous silicon film, anode potential-current characteristics and problems in application to integrated circuit were investigated. As a result, characteristics in anodization and oxidation peculiar to the injection type IPOS scheme were found. Satisfactory results about the isolation characteristic make it clear that this scheme can be applied to isolation in integrated circuit.

Electrostatic probe characteristics for a spherical probe in a slightly ionized continuum plasma

Current—potential characteristics have been calculated for spherical probes in a slightly ionized continuum plasma with the parameter ranges of ϵ (ion/electron temperature) 0.01, 0.1, 0.5, 1.0; ρ p (probe radius/plasma Debye length) 5, 10, 20, 30; and 0 < y p < 7 where y p is the normalized probe potential.

Novel Semiconducting Electrodes for the Photosensitized Electrolysis of Water

not Available.

Anomalous photoresponse of n-TiO2 electrode in a photoelectrochemical cell

The current-potential characteristics of n-TiO2 electrodes have been investigated in a photoelectrochemical cell. Photoresponse induced by the light of energy lower than the band gap of TiO2 has been observed in the potential range between −1.0 and −1.4 V vs SCE in 1N NaOH. The photoresponse, which is sensitive to the oxygen gas dissolved in solution, has been attributed to some surface states at the TiO2-electrolyte interface.

Etude du comportement anodique de l'interface fer-acide nitrique a l'aide d'une regulation a resistance negative

It is shown that potentiostatic regulation does not allow of a complete study of the current-potential characteristics of Fe in HNO 3. This difficulty has been overcome satisfactorily by using a control device of the interface polarization having a negative internal resistance. The polarization curves are very similar to those obtained in a sulphuric medium if the concentration of HNO 3 is lower than 7N whereas at concentrations higher than 7 N, they are very different. The analysis of the polarization curves associated with impedance diagrams plotted at different polarization points showed how the stable steady state of Fe is established when it is immersed in HNO 3 of various concentrations. By separating the anodic current, corresponding to the iron dissolution, and the cathodic current. corresponding to the NO − 3 reduction, from the observed overall current, strong reciprocal effects of these two processes have been found. Eliminating NO − 2 by addition of p-nitroaniline in the electrolyte, one could withdraw the effect of cathodic processes on the Fe dissolution. It permitted a clear demonstration that the particular behaviour of Fe in HNO 3 is due essentially to the reducibility of NO − 3.

Current potential characteristics of Zn/electrolyte and ZnO/electrolyte contacts

With regard to corrosion phenomena of zinc in solutions containing 0.1 M borax, potentiodynamic current-potential characteristics and open-circuit potentials of rotating disk electrodes made of Zn and ZnO have been investigated. Measurements were carried out at a constant temperature of 25 °C with various Zn 2+ concentrations, O 2 partial pressures and rotation speeds. Below Zn 2+ saturation and without dissolved oxygen it is observed that corroding Zn electrodes behave like metal electrodes in equilibrium with ZnO, and that with Zn 2+ saturation they behave like pure n-conducting ZnO electrodes. In the presence of dissolved oxygen two different diffusion controlled electrode reactions are observed, which are due to reduction of O 2 to H 2O 2 and O 2 to OH -. Because of the low electron density at the surface with Zn 2+ saturation the first reaction degenerates to a small current peak and is probably caused by a kind of O 2 adsorption.

Catalytic Reactions on Li-Doped NiO Using Modulation-Spectroscopy

The oxidation degree of nickeloxide-electrodes in aqueous solutions depends on the electrode potential, as it is known from the surface of passive nickel-electrodes. In addition to current-potential characteristics and the impedance of the solid state/electrolyte interface this behavior was investigated using modulated reflectance measurements. By modulating the electrode potential this method results in changing the oxidation degree in connection with the optical properties of a surface layer. The investigation of Li-doped (0.5–5 mol%) nickeloxide crystals shows, that the change of the oxidation degree is catalytically influenced by the Li-doping. Measurements of the modulated reflectance result that the electrochemical activity of the doped crystals increases approximately parabolic with rising Li-amount.

Comparison between the constant-potential steps of two point-contact Josephson junctions

Microwave-induced steps in the current-potential characteristics of two niobium point-contact junctions have been compared using a SQUID voltmeter with a resolution of less than 10−12 V. It has been established that the uncertainty in step potential at the 1-mV level is less than 2 in 109.

Contingent negative variation (CNV). Correlations with psychiatric diagnosis.

Slow potential responses of 14 schizophrenic, 12 manic, and 14 depressed patients were studied when they were exhibiting acute symptoms and were medication free. Ten normal adults served as a control group. Statistically significant differences were demonstrated between the patients and normals. In the latter, a typical CNV appeared with warning-imperative stimulus contingencies. There was very little discrimination between resting and response activity in manic and depressed patients. Waveforms in the schizophrenics were more variable with negative potential changes after motor response. No other clinical correlates with direct current potential characteristics were identified. Test retest profiles were generally stable in all subjects, with some exceptions associated with somatic treatment.