Hydrogen Evolution Current Research Articles

Role of prior cathodic polarization in the pitting corrosion of pure aluminium in acidic chloride solution

Role of prior cathodic polarization in the pitting corrosion of pure aluminium (Al) has been investigated in aqueous 1 M HCl solution (pH 0) using a potentiostatic current transient technique combined with an electrochemical quartz crystal microbalance technique, impedance spectroscopy and scanning electron microscopy (SEM). From the analysis of the first period of combined cathodic current transient and electrogravimetric curves, it is suggested that the hydrogen evolution current starts obeying the Tafel relation via proton absorption, formation of such hydrogen-containing species as OH − ions and/or H 2 O molecules within the native oxide film and proton reduction at the metal/oxide interface. During the second period appearing at potentials −1.5 and −1.7 V SCE (SCE, saturated calomel electrode) hydrogen evolution may occur at an enhanced rate at the bottom of micro-pits, formed due to local breakdown of the oxide film. This breakdown was ensured by the more abrupt decrease in oxide film resistivity ρ ox values with increasing prior cathodic polarization, calculated at −1.5 and −1.7 V SCE , from the analysis of the measured impedance spectra as compared to that reduction in ρ ox calculated at −1.0 V SCE . The surface area of the pitted specimens was quantitatively estimated from the measured capacitance values to increase with rising prior cathodic polarization, as evidenced by SEM. This means that the exposed metal surface at the bottom of micro-pits formed during prior cathodic polarization serves as a preferential site for Cl − ion attack during the following anodic polarization. Hence, a sufficient prior cathodic polarization for the formation of the micro-pits is a necessary condition for the promotion of pitting corrosion of pure Al.

Electrochemical Removal of Lead Ions from Flowing Electrolytes Using Packed Bed Electrodes

Packed bed electrodes, made of stacked screens, have been used as cathodes for the removal of lead ions from flowing alkaline electrolytes. We consider the coulombic efficiency , where and are, respectively, the lead deposition and hydrogen evolution currents, and the collection efficiency given by , where is the geometric limiting current for lead deposition, ν is the electrolyte flow rate, and is the feed concentration of lead ions. Two regions are defined in the current‐ potential relations, depending on whether hydrogen evolution does, or does not, contribute to the measured current, corresponding to ξ less than, or equal to, 100%, respectively. The geometric limiting current, , increases with increase of ν, electrode thickness (L), or specific surface area (S), and with decrease of the viscosity of the electrolyte (μ). The collection efficiency (ψ) increases as ν or μ decreases and L and/or S increases. Operating the cell at higher flow rates increases the overall coulombic efficiency, over a broader range of cell currents. It also increases the geometric limiting current although it decreases the collection efficiency. © 1999 The Electrochemical Society. All rights reserved.

An in-situ and ex-situ study of chloride adsorption on Cu(111) electrodes in dilute HCl solutions

The adsoprtion of Cl − on a Cu(111) electrode surface in acidic chloride solutions was studied in situ by cyclic voltammetry and scanning tunneling microscopy (STM) and ex situ by ultrahigh vacuum based spectroscopies. The voltammogram shows adsorption and desorption peaks superimposed by the hydrogen evolution current. By a combination of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and low energy ion scattering spectroscopy the adsorbate was unambiguously identified as Cl −. The presence of the hydrogen evolution current induces changes of the interface composition after the emersion, obfuscating the potential dependence of the Cl coverage in the ex situ experiments. This problem is circumvented by using mixed electrolytes. In the STM measurements the adsorption and desorption of Cl − was tracked in situ. The structure of the adsorbate layer was identified as (√3 × √3)R30.

Corrosion of stainless steels in acid solutions with organic sulfur-containing compounds

The influence of the organic sulfur-containing compounds on the corrosion of ferrite and austenitic stainless steels in sulfuric acid was studied. The results showed that the anodic dissolution and self-corrosion of stainless steels were remarkably accelerated in solutions with a low amount of the organic sulfur-containing compounds (0.02 mmol/dm 3). With an increase of the organic sulfur-containing compound concentration, more and more the organic sulfur-containing compound molecules adsorbed on the electrode surface and segregated the metal surface from the solution, which caused the decrease of the anodic dissolution and hydrogen evolution current of stainless steels. The anodic polarization behaviors of stainless steels were also changed with the various types of the organic sulfur-containing compounds and stainless steels.

The additivity of catalyzed hydrogen evolution currents of hemoglobins: an empirical approach

Abstract The additivity of catalyzed hydrogen evolution currents in solutions of hemoglobins (Hb), binary with respect to these compounds, was studied by d.c. polarography in ammonia buffer solutions containing Co(II). The solutions contained two different hemoglobins, each having different numbers of SH groups in the molecule. The composition of the hemoglobin mixture was changed, either keeping [Hb(1)] + [Hb(2)] constant, or [Hb(1)] + [Hb(2)] variable but [Hb(1)] constant. The experimental results were compared with the sum Is of catalytic currents of the constituent Hb species, taken from their experimental catalytic current-hemoglibin concentration relationships. The catalytic currents were evaluated taking into account no preferential adsorption of any hemoglobin in the formation of Is, or preferential adsorption of Hb(1) or Hb(2). In general, five types of additivity were proposed. Calculated total currents were compared with experimental data. It was proved that in all cases experimental currents were much lower than the Is obtained assuming no preferential adsorption of any hemoglobin. This testifies to some interactions between constituent hemoglobins of the mixture in the adsorption layer, causing a considerable reduction of the total current. Results concerning tested types of additivity proved that experimental results are best approximated by the calculated catalytic currents, if preferential adsorption of the hemoglobin containing more SH groups is assumed. Some remarks regarding the practical application of catalytic current measurements to solutions containing mixtures of proteins are given.

Electrowinning of Non‐Noble Metals with Simultaneous Hydrogen Evolution at Flow‐Through Porous Electrodes: I . Theoretical

A mathematical model, is developed to simulate the electrowinning of non‐noble metals (e.g., Zn, Cr) within flow‐through porous electrodes under the conditions of simultaneous evolution of hydrogen gas bubbles. The results of the model are presented as a function of several dimensionless groups representing kinetics, mass transfer, ohmic resistance, and gas bubbles. These coupled, nonlinear effects are investigated by examining the distributions of the metal reduction and hydrogen evolution currents, coulombic efficiency of the metal electrowinning reaction, and gas void fractions under a series of limiting conditions. The gas bubbles accentuate the nonuniform distribution of the potential and the currents of both reactions by increasing the effective resistance of the gas‐electrolyte dispersion filling the pore space. This results in the underutilization of the internal surface area of the porous electrode and accelerates preferential localized plugging of the pores with the reduced metal. It can also instigate localized mass‐transfer limitations, i.e., the polarization at some points within the pores becomes large enough to support the limiting current of the metal deposition reaction (i.e., it becomes mass‐transfer controlled) while at other points lower polarizations and hence smaller currents prevail. Consequently, the optimum current which maximizes the removal rate of the metal is shown to be well below the theoretical limiting current of the electrode. This optimum current is significantly influenced by the evolving hydrogen gas bubbles. Neglecting this phenomenon leads to erroneous design and operational considerations.

A quartz crystal microbalance study of the corrosion of iron thin films in neutral aqueous solutions

Abstract The quartz crystal microbalance (QCM) technique is capable of detecting small mass changes in the region of nanograms per square centimetre from resonant frequency changes of the quartz crystal. In this study, the QCM technique, combined with electrochemical measurements, was applied to the minute corrosion of iron thin films in deaerated neutral solutions. An iron thin film with a thickness of 200 nm was electroplated on the gold electrode of a quartz crystal. The mass changes of the iron thin film during natural immersion or galvanostatic polarization in deaerated pH 6.48 borate solution, pH 6.42 borate solution with 10−2 M chloride ions, pH 6.0 borate solution with 0.5 M chloride ions and pH 6.48 phosphate solution were measured as a function of time or potential to evaluate the iron dissolution rate or iron dissolution current. The corrosion rate of the iron thin film on natural immersion increased in the order pH 6.48 phosphate > pH 6.0 borate with 0.5 M chloride ions > pH 6.42 borate with 10−2 M chloride ions > pH 6.48 borate solution. The net current flowing through the external circuit during galvanostatic polarization near the corrosion potential was successfully separated into the iron dissolution current and hydrogen evolution current. Tafel plots of the iron dissolution current and hydrogen evolution current were made to evaluate the corrosion mechanism of the iron thin film. The Tafel slopes of iron dissolution and hydrogen evolution thus obtained depend on the electrolyte solutions, from which conclusions can be drawn on the corrosion mechanism.

The underpotential deposition of zinc for mitigation of hydrogen absorption and penetration into HY-130 steel

It is shown that underpotential deposition of zinc from a plating solution inhibited the discharge of hydrogen on HY-130 steel. In the presence of a monolayer coverage of Zn, hydrogen evolution currents were reduced by 58% compared with values obtained on bare HY-130 steel. The observed effects are due to the kinetic limitations of the hydrogen discharge reaction and the suppression of hydrogen absorption by the deposited monolayers. The hydrogen atom direct entry mechanism was used and a mass transfer term was introduced into the permeation model to interpret the experimental data. In the presence of zinc monolayers, the hydrogen entry efficiency in the alloy and the hydrogen entry rate constant were reduced by a factor of three and by 74%, respectively.

Surface Treatment for Mitigation of Hydrogen Absorption and Penetration into AISI 4340 Steel

The effectiveness of underpotential deposition of Pb onto a membrane made of AISI 4340 steel on the reduction of the hydrogen evolution reaction on the membrane and the degree of hydrogen ingress into the membrane was determined. In the presence of a monolayer coverage of Pb on the membrane surface, the hydrogen evolution currents were reduced by a factor of two compared with the values obtained on bare steel, and the steady‐state hydrogen permeation flux through the steel membranes was reduced by 71%.

High-performance liquid chromatography of thiols with differential pulse polarographic detection of the catalytic hydrogen evolution current

SH and SS groups in organic compounds were sensitively detected in NH 3-NH 4Cl (0.24 M)-Co 2+ (5 · 10 −4 M) solution by differential-pulse polarography (DPP). A new type of flow-through cell was developed and used to combine the polarograph with a high-performance liquid chromatograph. The experimental conditions for polarography and chromatography were studied and the effectiveness of the cell was also evaluated. The chromatogram obtained showed that this combined system works very well for the detection of thiols. The sensitivity was similar to that given by UV detection but was not handicapped by the wavelength. As a negative potential was used, the coexistence of other species did not cause large interferences.

Evaluation of Alloy Anodes for Aluminum‐Air Batteries: II . Delineation of Anodic and Cathodic Partial Reactions

The design, calibration, and operation of a source/collector electrochemical cell for delineating anodic and cathodic partial currents for reactive metals in aqueous media is described. This cell has been used to measure the hydrogen evolution current on aluminum and aluminum alloys in at 25°, 50°, and 80°C over a wide range of potential. These data were then combined with the total current to calculate the anodic partial current as a function of potential. The data show that aluminum is a passive metal in at 25° and 50°C, but that at 80°C it undergoes transpassive dissolution over the entire potential range that is accessible.

Electrochemical analysis of antitumour platinum drugs and their complexes with DNA

The electrochemical behaviour of platinum anticancer drugs has been evaluated using voltammetric techniques in connection with mercury electrodes. Most platinum cytostatics and their model platinum compounds are electroreduced or yield catalytic hydrogen evolution currents at mercury electrodes. These currents can be exploited for very sensitive analysis of platinum compounds in biological samples. Polarographic techniques provide valuable information on the conformational alterations induced in genetic material by the binding of platinum cytostatics. Polarographic analysis reveals a very good correlation between the anticancer activity of platinum drugs and the type of damage to DNA induced by the attack of the drug. Moreover, an approach based on polarographic analysis of DNA makes it possible to explain the radiosensitizing effect of platinum complexes in biological systems.

Electrochemical analysis of antitumour platinum drugs and their complexes with DNA

The electrochemical behaviour of platinum anticancer drugs has been evaluated using voltammetric techniques in connection with mercury electrodes. Most platinum cytostatics and their model platinum compounds are electroreduced or yield catalytic hydrogen evolution currents at mercury electrodes. These currents can be exploited for very sensitive analysis of platinum compounds in biological samples. Polarographic techniques provide valuable information on the conformational alterations induced in genetic material by the binding of platinum cytostatics. Polarographic analysis reveals a very good correlation between the anticancer activity of platinum drugs and the type of damage to DNA induced by the attack of the drug. Moreover, an approach based on polarographic analysis of DNA makes it possible to explain the radiosensitizing effect of platinum complexes in biological systems.

Effect of Temperature on the Polarographic Catalytic Current Produced by Proteins in the Presence of Cobalt Salts

Abstract The effect of temperature on the polarographic catalytic hydrogen evolution current (Brdicka current) produced by ribonuclease-A in an ammoniacal buffer containing cobalt salt has been studied using the theoretical equation of Brdi\`{c}ka current. With increasing temperature, the Brdicka current at −1.3 V increased between 10 and 30 °C then fell off above 30 °C, whereas the currents at −1.4 and −1.5 V decreased continuously. Analysis showed that the initial increase of the Brdicka current at −1.3 V was only apparent and that the Brdicka current constant, kB, which represents the catalytic activity of the protein, always decreased with increasing temperature in the potential range of −1.3 to −1.5 V. Further analysis has revealed that the intrinsic catalytic activity of the protein-cobalt(0) complex, which is transiently formed on the electrode surface and which catalyzes the hydrogen evolution, increases with increasing temperature whereas the life time of the complex decreases and the latter decrease cancels the former increase, resulting in the decrease of the kB value with increasing temperature.

Stripping analysis of zinc in natural waters utilizing the medium exchange method

Stripping analysis with medium exchange is employed for the flow analysis of zinc in natural waters. In order to minimize the interference due to the hydrogen evolution current, that masks the zinc peak in analysis of acidified natural waters, more suitable electrolyte is transferred (following the deposition step) into the detector. A flow cell with a stationary mercury film disk electrode is employed. Measurements can be performed in the presence of oxygen in the sample solution, utilizing an oxygen free exchange solution.

Polarographic reduction of aldehydes and ketones XX. Electroreduction of benzocyclenones

Reduction of indanone (I), tetralone (II) and benzosuberone (III) was studied by d. c. and pulse polarography, cyclic voltammetry and controlled potential electrolysis with a dropping mercury electrode in aqueous solutions containing 2% ethanol at various pH values. In acidic media the protonated form, at higher pH values the free carbonyl form is reduced. The reduction of the unprotonated form is accompanied by protonation of the radical anion formed. The behavior of all three ketones I–III in this pH region is similar and differs only in the half-wave potential values and the rates of protonation of the radical anion. The reduction of the protonated form is affected both by differences in potentials of the ketones I–III and by differences in the rates of protonation, but most significantly by the half-wave potential of the radical formed in the first electron uptake. For indanone (I) this reduction is so positive that only one two-electron step is observed. For benzosuberone (III) the half-wave potential of this reduction is sufficiently more negative than the first electron uptake and two one-electron separated waves result. For tetralone (II) the reduction of the radical occurs at so negative a potential that it is overlapped by the hydrogen evolution current. Only one one-electron wave is thus observed. The effect of ring size on potentials and protonation reactions is discussed from the point of view of ring strain, adsorbability and radical stability.

Polarographic reduction of aldehydes and ketones: XX. Electroreduction of benzocyclenones

Summary Reduction of indanone (I), tetralone (II) and benzosuberone (III) was studied by d. c. and pulse polarography, cyclic voltammetry and controlled potential electrolysis with a dropping mercury electrode in aqueous solutions containing 2% ethanol at various pH values. In acidic media the protonated form, at higher pH values the free carbonyl form is reduced. The reduction of the unprotonated form is accompanied by protonation of the radical anion formed. The behavior of all three ketones I–III in this pH region is similar and differs only in the half-wave potential values and the rates of protonation of the radical anion. The reduction of the protonated form is affected both by differences in potentials of the ketones I–III and by differences in the rates of protonation, but most significantly by the half-wave potential of the radical formed in the first electron uptake. For indanone (I) this reduction is so positive that only one two-electron step is observed. For benzosuberone (III) the half-wave potential of this reduction is sufficiently more negative than the first electron uptake and two one-electron separated waves result. For tetralone (II) the reduction of the radical occurs at so negative a potential that it is overlapped by the hydrogen evolution current. Only one one-electron wave is thus observed. The effect of ring size on potentials and protonation reactions is discussed from the point of view of ring strain, adsorbability and radical stability.

Hydrogen adsorption on platinum, iridium and rhodium electrodes at reduced temperatures and the determination of real surface area

Cyclic voltammograms of platinum and iridium electrodes in 5 M sulphuric acid at −72°C display much greater separation of the hydrogen adsorption and evolution currents than at 20°C. This enables the saturation hydrogen coverage and the real surface area of an electrode to be determined directly from the voltammogram. The adsorption of hydrogen on rhodium is not sufficiently rapid to maintain equilibrium on a voltammogram at reduced temperatures, and the saturation hydrogen coverage cannot be obtained directly. The accuracy of determination of surface area for the three metals from measurements at 20–25°C is discussed. The voltammograms for platinum electrodes at −72°C do not show the “third anodic hydrogen peak” observed at 20°C. The processes which have been suggested to account for this peak are discussed.

Hydrogen adsorption on platinum, iridium and rhodium electrodes at reduced temperatures and the determination of real surface area

Cyclic voltammograms of platinum and iridium electrodes in 5 M sulphuric acid at −72°C display much greater separation of the hydrogen adsorption and evolution currents than at 20°C. This enables the saturation hydrogen coverage and the real surface area of an electrode to be determined directly from the voltammogram. The adsorption of hydrogen on rhodium is not sufficiently rapid to maintain equilibrium on a voltammogram at reduced temperatures, and the saturation hydrogen coverage cannot be obtained directly. The accuracy of determination of surface area for the three metals from measurements at 20–25°C is discussed. The voltammograms for platinum electrodes at −72°C do not show the “third anodic hydrogen peak” observed at 20°C. The processes which have been suggested to account for this peak are discussed.

Limiting oxygen coverage on platinized platinum; Relevance to determination of real platinum area by hydrogen adsorption

A limiting oxygen coverage is found on platinized platinum electrodes and identified as a monolayer of chemisorbed oxygen atoms. Evidence is presented to support a realistic separation of hydrogen adsorption and evolution currents on linear sweep voltammograms in order to determine the hydrogen monolayer charge. Comparison with the hydrogen monolayer charge shows the stoichiometry of the oxygen monolayer to be 2 oxygen atoms/surface platinum atom for both smooth and platinized platinum electrodes. The problems involved in interpreting hydrogen adsorption measurements in terms of real electrode areas are discussed.