Reduction Of Hydrogen Ions Research Articles

Effects of alloying elements and binder on the electrochemical behavior of metal hydride electrodes in potassium hydroxide electrolyte

This investigation examines the effect of alloying elements on the charge–discharge performance of LaNi3.6(Co+Mn+Al)1.4 electrodes in 7 M KOH electrolyte. The activation behavior and the effect of binder content were also examined. Both half-cell and full-cell systems were employed to evaluate the electrochemical performance. Experimental results indicated that a few cycles of charge–discharge at a rate of 150 mA/g in 7 M KOH electrolyte were sufficient to activate the freshly prepared LaNi3.6(Co+Mn+Al)1.4 electrodes. The amount of binder affected the activation behavior, the overvoltage for hydrogen ions reduction and the discharge capacity of the MmNi3.55Co0.75Mn0.4Al0.3 electrode. In the alloy of the LaNi3.6(Co+Mn+Al)1.4 electrodes, a high Co content helped to promote both the capacity at a relatively low discharging rate and the cyclic life. An increase of the Al content raised the discharge voltage and improved the high rate discharge capacity, but reduced the cyclic stability. The alloy with a high Mn content required the least cathodic polarization during charging but had the lowest discharge capacity at a rather high discharging rate.

Effect of Sodium Hydroarsenate on the Kinetics of Reduction of Hydrogen Ions at Iron and on the Hydrogen Diffusion through a Steel Membrane from Aqueous and Ethylene Glycol Solutions of Hydrochloric Acid

Effect of arsenic compounds H3AsO4, H2AsO4 –, and HAsO4 2– on the hydrogen overvoltage, the slow stage of discharge of hydronium ions on the Armco iron, and the hydrogen diffusion through a steel membrane from aqueous and ethylene glycol solutions of hydrochloric acid with a constant ionic strength of unity is considered.

Comparison of the spontaneous and anodic processes during dissolution of brass

The results of investigations on spontaneous dissolution of α, β ′, γ and ϵ-brasses in non-complexing, oxidant free acid solutions (2.0 M H 2SO 4) have been compared with literature results of anodic dissolution of these alloys. In anodic process the Cu-enriched intermediate phases are created while during spontaneous process dezincification leads to the creation of a layer of pure copper. Occurrence of Cu-rich intermediate phases has not been seen during spontaneous dissolution of β ′ and γ-brasses. As a result of a consecutive reaction, however, copper hydride is created. It appears that the spontaneous dissolution of brasses is related to the mechanism of creation and growth of a new copper phase. It seems that the main difference between those two processes consists in the appearance of hydrogen ions reduction, which is absent during anodic dissolution. It has been suggested, that reduction of the hydrogen ions is responsible for the change of the mechanism, of brass dissolution, from the anodic to spontaneous one.

Electrochemical dissolution of tin in methanesulphonic acid solutions

High-rate electroplating of tin on a moving steel strip is generally carried out in cells with dimensionally stable anodes. To obtain a matt tin deposit a concentrated acidic tin methanesulphonate solution containing a small concentration of sulphuric acid is used. The concentrated tin methanesulphonate solution is prepared by dissolution of tin particles with oxygen in a special column. To describe this dissolution process electrode reactions (namely, reduction of oxygen, hydrogen peroxide and hydrogen ions on a tin electrode and oxidation of tin) were studied using electrochemical techniques. It was concluded that on tin, oxygen is almost entirely reduced to water and that H2O2 cannot corrode tin directly, but its decomposition products, for instance oxygen, can. The exchange current density and the charge transfer coefficient for the investigated electrode reactions are estimated. The dissolution of tin by oxygen is determined by the kinetic parameters of the oxygen reduction reaction and by the mass transfer of (i) dissolved oxygen to and (ii) Sn2+ ions from the tin electrode surface. Hydrogen evolution can be neglected during the dissolution of tin in the presence of oxygen. Moreover, it was found that the rate of tin corrosion increases with (i) increasing H+ concentration, (ii) oxygen concentration, (iii) convection intensity and (iv) temperature. It is likely that the tin surface is not covered with oxygen during corrosion in pure methanesulphonic acid solutions, but an oxide layer may be present on the tin surface during oxygen corrosion in pure sulphuric acid solutions. This oxide layer may hinder the oxygen corrosion of tin.

Interrelation between kinetics of the hydrogen ion reduction on iron and the hydrogen diffusion flux into carbon steel in acidic solutions

Kinetic parameters of discharge of hydrogen ions, which depend on the nature of the slow stage in the Volmer–Tafel and Volmer–Heyrovský mechanisms, are obtained theoretically for commensurate rates of successive reactions on energetically-uniform and evenly-nonuniform surfaces. The results are compared with similar experimental parameters for the Armco iron in the system C2H4(OH)2–H2O + HCl. Upon adding 2–10 wt % H2O into C2H4(OH)2, the slow discharge stage gives way to the Tafel reaction if the hydrogen ion adsorption obeys the Temkin isotherm. Upon going to purely aqueous solutions, the discharge process becomes the limiting stage again. A change in the hydrogen diffusion flux through a steel membrane from these mixed solvents does not correlate with the nature of the stage that controls the cathodic reduction of hydrogen ions.

High-voltage electrodeposition conditions in the stripping voltammetry of metal ions: A mechanism and analytical prospects of the process

It was found that the exaltation phenomenon in the parallel reduction of hydrogen ions from weak acids or water is responsible for the acceleration of the electrodeposition of metals under high-voltage conditions. Under these conditions, the rate of electrodeposition can be increased by 2 to 3 orders of magnitude compared to the rates of electrodeposition under standard conditions. At a constant high voltage of electrodeposition, the stripping peak currents of metals are proportional to the deposition time and the bulk concentration of analyte ions. Exaltation phenomena can be used in analysis not only for intensifying the process, but also for lowering the limit of detection, improving the selectivity, and decreasing the adverse effect of surfactants.

Electroreduction of chromic acid during the chromium deposition: An RRDE study

The rate of the trivalent chromium ion formation during the chromic acid reduction in the presence of sulfate ions is studied in a wide potential range by the RRDE method. At potentials of incomplete reduction of chromate ions, the reaction is attendant by a side process (probably, the hydrogen ion reduction). With a phase film covering the disk cathode, the ring current does not correspond to the number of Cr(III) ions formed at the disk, rather it characterizes the oxidation of products of a phase film comprising oxide-hydroxide compounds of Cr(III). The hypothesis about the formation of a phase cathodic film, presumably preceding the metallic chromium deposition, is confirmed experimentally. The oxide-hydroxide species of Cr(III), which are main film-forming substances, undergo phase transitions in a zone that depends on the sulfate ion concentration. The phase transitions whose products may reach the ring electrode occur in the near-electrode layer. The lower the sulfate ion concentration, the larger the extension of the layer.

Effect of oxygen and hydrogen sulfide on carbon dioxide corrosion of welded structures of oil and gas installations

1. It is proved that CO2 corrosion of carbon steel increases by 1.5–2 times with increase of H2S content in the mixture (pH2S<0.5 MPa) in the temperature range 20–80°C. Further increase in H2S content (pH2S≥0.5–1.5 MPa) weakens corrosion, especially in the temperature range 100–250°C, because of influence of FeS and FeCO3 on corrosion. 2. It is shown that with increase of O2 concentration in the mixture (pO2=0–1.5 MPa) the CO2 corrosion rate increases 3–4 times in the temperature range 40–80°C. As the temperature rises to 100–250°C, oxygen hardly exerts any effect on the corrosion rate. 3. A scheme is proposed to classify processes of CO2 corrosion of carbon steel into three types based on the type of corrosion products formed, which enables one to evaluate the effect of combined influence of H2S, O2, and temperature on the nature of CO2 corrosion. 4. The thermodynamic potential of formation of CO2 corrosion products (FeS and FeCO3) upon interaction between the mixture containing CO2 and H2S and the carbon steel sample surface has been calculated; the equilibrium conditions for the formation of metastable FeS and its dissolution in the main corrosion product, viz., FeCO3, have been determined. 5. It has been shown that the combined effect of H2S and O2 on the CO2 corrosion process, consists in acceleration of cathodic reaction of hydrogen ion reduction.

Hard chromium plating on cold swaged Cr-Mo steel using rotating cylinder electrode

Hard chromium plating is widely used owing to its good wear and corrosion resistance. This plating technology has been practiced and well developed for many decades [1, 2]. Since reduction of hydrogen ions occurs at electrode surface during chromium plating, the current efficiency for the plating is normally under 25% [1]. However, Hoare [3] shows that rapid flow of the electrolyte over the cathode surface is essential for highspeed chromium plating due to the reduction of the diffusion path in a diffusion-controlled electrode reaction. Plating by using rotating disc electrode (RDE) method is useful to study this effect. Cross-section microstructure of the plated hard chromium was studied with optical microscope and scanning electron microscope (SEM) [4, 5]. The results showed that the grain size of as-plated chromium was so fine that the grain size cannot be estimated, and only the grains after annealing can be observed. Pina [5] showed that a fiber texture existed with 〈111〉 axis perpendicular to the chromium deposit surface by using X-ray diffraction method. The interface microstructure between Cr-Mo steel and chromium deposit has not been studied yet. Especially, little work has been done on the current efficiency and TEM-cross section microstructure of chromium plating using rotating cylinder electrode (RCE), by which a uniform mass transport over all of the electrode surface can be obtained. In this letter the aspects mentioned above are reported using RCE specimens. Cold swaged Cr-Mo steel was the chosen specimen with its chemical composition shown in Table I. The cylinder specimen dimension was 16 mm φ× 5 mm with an exposing plating area of 2.51 cm2. Platinized-Ti mesh with dimension of 25× 35 mm was used as anode. All chromium plating was performed in a conventional bath containing 250 g/l of CrO3 and 2.5 g/l of H2SO4 at 50 ◦C. Cathodic current densities applied were 30, 40, 50 and 60 A/dm2, respectively. Rotating speed of RCE was controlled in the range of 5–1000 rpm. Before electroplating, the RCE specimens were anodically polarized with current density of 40 A/dm2 at 200 rpm for 30 s. The current efficiency was evaluated with three RCE specimens after a constant applied cathodic charge of 1.33 A h under same plating condition. The weight increment of chromium plating was measured and compared with theoretical weight increment according to Faraday’s law. After plating, the RCE specimen was rinsed in acetone, dried with hot air, then prepared for current efficiency evaluation; TEM-cross section specimens were prepared as mentioned elsewhere [6] and their microstructure examined. The current efficiency of applied cathodic current density with respect to logarithmic rotating speed of RCE is shown in Fig. 1. The results show that all current efficiency increases with the increasing of cathodic current density, suggesting that higher electric field tends

The Strength of Acids in Alcohols As Determined by Steady-State Voltammetry

Steady-state voltammograms for reduction of acids of various strengths in alcohols with excess supporting electrolyte and without any supporting electrolyte can be used to infer charge type and strength of the acid on the basis of the phenomenon of migration. For strong and moderately weak acids (K(a)/[Formula: see text] > 10(-)(3)) in alcohols, the ratio of steady-state transport-limited current to diffusion-limited current, corrected appropriately for ion-ion interactions, the presence of ionic impurities, and changes in viscosity, for hydrogen ion reduction without supporting electrolyte and with excess supporting electrolyte equals 2. For acetic acid, which is very weak (K(a)/[Formula: see text] < 10(-)(6)), the value of the steady-state transport-limited current is, under the experimental conditions applied here, independent of supporting electrolyte concentration. In the case of a homogeneous acid-base equilibrium, a novel analytical procedure yields diffusion coefficients of both hydrogen ion and undissociated weak acid molecules from the diffusional and migrational currents. Limiting currents obtained in alcohols with excess supporting electrolyte and without supporting electrolyte are compared by means of an extended formula that incorporates the ionic strength dependence of diffusion coefficients.

Impact of Graphite Gasket/Duplex Stainless Steel Couples on Crevice Chemistry and the Likelihood of Crevice Attack in Seawater

Abstract Electrochemical polarization measurements were made on a graphite laminate gasket and a super-duplex stainless steel (DSS) in deaerated 1 M sodium chloride (NaCl) solution over a range of pH. The open-circuit potential of the graphite was significantly more noble than that of the DSS, and the kinetics of the hydrogen ion reduction were greater at potentials more positive than ∼ 0.0 VSCE. Data were used as input to a model of crevice chemistry, and predictions were made for potentials up to 0.4 VSCE. For crevices of parallel plates of DSS-DSS and DSS-plastic, the usual acidic conditions were predicted. However, for a DSS-graphite combination, there was no significant decrease in pH. The latter was a consequence of the enhanced kinetics for cathodic reduction of hydrogen ions and water on the graphite which, when confined within the crevice, opposed the fall in pH associated with the metal-ion hydrolysis process. The predictions suggested that coupling to graphite, contained within the crevice, may...

Catalytic hydrogen evolution in the presence of methylthiohydantoin–glycine and cobalt(II) ion: a study by cathodic stripping voltammetry at a hanging mercury drop electrode

The carbon–sulfur bond in methylthiohydantoin–glycine (MTH–Gly) is broken during the deposition on the mercury electrode at potentials around −0.1 V versus SCE, giving mercury sulfide which is detected by the characteristic cathodic peak at −0.7 V. If cobalt (II) is also present, the product of the deposition step is a mixture of mercury and cobalt sulfides. During the cathodic scan, the last one is reduced to a transient Co(0) species that catalyses the reduction of hydrogen ion to the hydrogen molecule by a mechanism alike to that emphasized for the Co(II)-sulfide ion system (F.G. Bănică, N. Spătaru, T. Spătaru, Electroanalysis 9 (1997) 1341). This electrode process induces a cathodic peak at −1.4 V that enables the determination of MTH–Gly down to 10 −7 M in the borax buffer at pH 8.5. The possible extension of this method to other classes of organic sulfur compounds is briefly discussed.

Electrodialysis of Vanadium(III) and Iron(II) Ions from a Simulated Decontamination Solution

The transport of vanadium(III) and iron(II) ions through the Nafion 117 cation-exchange membrane in the presence of picolinic acid was investigated by simulating the equilibrium distribution of ionic species as a function of pH, and by electrodialyzing the simulated waste solution. From distribution calculations of the model reaction systems it could be predicted that at pH 1.6 most vanadium ions exist predominantly in the form of the VIII(Pic−)2 + complex, and this form of complex permeates across the cation-exchange membrane during electrodialysis. The experimental results, including variations in the color and cation concentrations of the catholyte, confirm the existence of the vanadium(III) picolinate complex. Iron ions permeated into the catholyte were converted to their hydroxide precipitates, which could be formed at the high pH condition resulting from the reduction of hydrogen ions and the production of OH− ions by water electrolysis at the cathode. It was also found that the in-situ precipitation of iron in the electrodialyzer could be self-modulated by shifting the catholyte pH from the acidic state to the alkaline state during electrodialysis operation.

Adsorption of Thiourea on Copper Electrodes Monitored by In Situ Infrared Spectroscopy

In situ infrared (IR) spectroscopy was used to monitor the adsorption of thiourea onto copper electrodes in 0.5 M sulfuric acid solutions sunder cathodic polarization. At potentials negative of the open‐circuit potential, p‐polarized IR spectra provided evidence for the partial desorption of TU. The desorption had a reversible character as indicated by the recovery of the spectra upon reestablishing open‐circuit conditions. Thiourea bands appearing in s‐polarized spectra at very negative potentials were attributed to deprotonation of thiourea within the thin‐layer gap of the cell resulting from hydrogen ion reduction. Both the bulk, s‐polarized, and surface, p‐polarized, spectra showed bipolar symmetric N‒C‒N vibrational bands. The bands were attributed to changes in N‒C‒N bond order resulting from protonation of the S atom or adsorption of the thiourea via the S atom, respectively.

Optimization of bath composition for hard Fe–C alloy plating

Fairly uniform Fe–C alloy deposits with bright appearance and characteristic black colour were obtained in Hull cell tests at 1.0A from baths with the following composition: FeSO4 0.5m or higher, citric acid 0.01m or lower, and pH around 2.0. The carbon content of the deposits from these baths ranged between 1.0 and 1.2wt% and the Vickers hardness was HV700 or above over a wide area of the Hull cell cathode. The thickness distribution of the deposits on the Hull cell cathode from these baths suggested that the current efficiency was 100% and the local current density obeyed the primary current distribution, except for the region near the low-current-density (LCD) end where the thickness decreased unexpectedly. The addition of chloride ion as NaCl, at concentrations of 1.0m or above, improved the thickness in the LCD region, and the thickness distribution on the Hull cell cathode suggested that current efficiency was 100% even at the LCD end. Chloride ion did no t affect the carbon content or the hardness of the deposits. Polarization measurements showed that the hydrogen ion reduction occurred at more noble potentials than Fe deposition. The unexpected thickness decrease near the LCD end, observed in Hull cell tests, and the improvement of this by adding chloride ion were both accounted for by the change in the preceding hydrogen ion reduction rate. The increase in citric acid concentration enhanced hydrogen ion reduction and therefore caused a lowering of current efficiency at low current densities. On the other hand, the addition of chloride ion inhibited hydrogen ion reduction and caused an increase in current efficiency at low current density.

A Comparative Electrochemical Study of Copper Deposition onto Silicon from Dilute and Buffered Hydrofluoric Acids

An electrochemical direct current polarization method was used to investigate characteristics of copper deposition onto silicon from dilute and buffered hydrofluoric acid solutions. The corrosion current density and corrosion potential of silicon were not very sensitive to the concentration, up to 1000 parts per billion, in buffered hydrofluoric acid. However, the extent of copper deposition, as measured by total reflection X‐ray fluorescence, increased as the concentration in solution increased. In dilute hydrofluoric acid, addition had a significant and systematic effect on the corrosion potential and corrosion current density of silicon. However, in both types of solution, the cathodic current calculated from the measured copper deposition was found to be only a small fraction of the corrosion current (less than 1%). This indicates that the primary cathodic reaction is not copper ion reduction but hydrogen ion reduction. Illumination affected the electrochemical behavior of both p‐ and n‐type silicon in spiked dilute hydrofluoric acid, but only that of p‐type silicon in buffered hydrofluoric acid.

Voltammetric Studies of Counterion Diffusion in the Monodisperse Sulfonated Polystyrene Latex

Steady-state voltammetry for the reduction of hydrogen ion at a Pt microelectrode was carried out in an aqueous suspension of a monodisperse sulfonated polystyrene latex with hydrogen ion as counterion to the latex particles. The measured transport-limited current for the reduction of the hydrogen ion was related to the gradient-diffusion coefficient of the hydrogen ion over a wide range of concentration of inert, 1:1 electrolyte. The gradient-diffusion coefficient for hydrogen ion in the deionized, ordered latex crystal was less than 1/40th of the value found without the latex. Addition of a 100-fold excess of electrolyte (with respect to hydrogen ion concentration) resulted in a value for the gradient-diffusion coefficient close to that without the latex. A neutral molecule, 4-hydroxy-TEMPO, oxidized anodically in the suspension under these same conditions yielded transport-limited currents that were little affected by changes in salt concentration. This suggests that most of the hydrogen ions are elect...

Voltammetry for Reduction of Hydrogen Ions from Mixtures of Mono- and Polyprotic Acids at Platinum Microelectrodes

The steady-state voltammetric behavior for reduction of several polyprotic acids and mixtures of strong and weak mono- and polyprotic acids was studied at platinum microelectrodes. The results demonstrated that over the potential range accessible to reduction of acids in water (up to ∼−1 V vs Ag/AgCl) via a preceding chemical reaction (CE mechanism), the reduction of weak polyprotic acids and mixtures of acids can produce either a single well-defined wave or two waves separated to a different extent, depending on the dissociation constant of each acidic form, on the analytical concentration of each acid, and on the mutual ratio of the acids present at equilibrium in the bulk solutions. The overall reduction mechanism for most of the mixtures examined was interpreted on the basis of a series of CE processes associated to the hydrogen evolution. This interpretation was supported by digital simulation procedures. A theoretical relationship for predicting the steady-state limiting current for any mixture of a...

Coupling microcalorimeter with electrochemical instruments for thermoelectrochemical research

A measurement system that couples a commercial microcalorimeter with usual electrochemical instruments was established for electrochemical calorimetry of electrode reactions. Apparent enthalpy change of anodic oxidation of ferrocyanide ion to ferricyanide ion and apparent enthalpy change of cathodic reduction of hydrogen ion to hydrogen gas were determined with this system. The difference between the apparent enthalpy change and the value calculated with conventional thermodynamic data of aqueous ions was found to be a constant at a given temperature. This system can further be used to determine unknown standard enthalpy changes of electrode reactions.

Voltammetric reduction of hydrogen ion in solutions of polyprotic strong acids with and without supporting electrolyte

Voltammetric reduction of strong polyprotic acids in solutions with excess and without supporting electrolyte was studied both theoretically and experimentally. A theoretical model based on the transport (diffusion and migration) equations and the electroneutrality principle was used to compute voltammograms by finite difference simulation under both steady state and transient conditions. Simulated voltammograms are compared with experimental reduction curves obtained at platinum microelectrodes without and with excess electrolyte for two strong polyprotic acids, sulfuric (H2SO4) and tungstosilicic (H4W12SiO40) acids. Perchloric acid (HClO4) was used as the reference for comparison. The experimental results agree well with the calculated voltammetric curves both without and with excess supporting electrolyte. The dependence of voltammetric response on the concentration of acids is also discussed.