Reduction Of Hydrogen Ions Research Articles

A Single Platinum Microelectrode for Identifying Soft Drink Samples

Cyclic voltammograms recorded with a single platinum microelectrode were used along with a non-supervised pattern recognition, namely, Principal Component Analysis, to conduct a qualitative analysis of sixteen different brands of carbonated soft drinks (Kuat, Soda Antarctica, H2OH!, Sprite 2.0, Guarana Antarctica, Guarana Antarctica Zero, Coca-Cola, Coca-Cola Zero, Coca-Cola Plus, Pepsi, Pepsi Light, Pepsi Twist, Pepsi Twist Light, Pepsi Twist 3, Schin Cola, and Classic Dillar’s). In this analysis, soft drink samples were not subjected to pre-treatment. Good differentiation among all the analysed soft drinks was achieved using the voltammetric data. An analysis of the loading plots shows that the potentials of −0.65 V, −0.4 V, 0.4 V, and 0.750 V facilitated the discrimination process. The electrochemical processes related to this potential are the reduction of hydrogen ions and inhibition of the platinum oxidation by the caffeine adsorption on the electrode surface. Additionally, the single platinum microelectrode was useful for the quality control of the soft drink samples, as it helped to identify the time at which the beverage was opened.

Non-equilibrium partial oxidation of TiN surface for efficient visible-light-driven hydrogen production

The non-equilibrium quick oxidation of titanium nitride (TiN) particles is found to be capable of kinetically controlling the partial oxidation on the surface and constructing a TiOxNy@TiN core–shell structure, in which the TiOxNy shell exhibits different components (x = 0.0–2.0). The TiOxNy@TiN structure can absorb visible light and display a high photocatalytic activity for hydrogen production, without any help from noble metal co-catalysts. A hydrogen generation rate of 506 μmol g−1 h−1 can be reached. The strong catalytic ability of TiOxNy@TiN can be attributed to the formation of heterojunction among the hybrid TiOxNy, which can facilitate the separation of light-induced electron–hole pairs. Furthermore, the non-equilibrium quick oxidation leads to the partial survival of electro-conductive TiN tiny crystals on the surface, which can act as co-catalysts to further improve the electron–hole separation and to catalyze hydrogen ion reduction.

Modeling of SCC initiation and propagation mechanisms in BWR environments

During operation of mainly BWRs’ (Boiling Water Reactors) excursions from recommended water chemistries may provide favorite conditions for stress corrosion cracking (SCC). Maximum levels for chloride and sulfate ion contents for avoiding local corrosion are therefore given in respective water specifications. In a previously published deterministic 288 °C – corrosion model for Nickel as a main alloying element of BWR components it was demonstrated that, as a theoretically worst case, bulk water chloride levels as low as 30 ppb provide local chloride ion accumulation, dissolution of passivating nickel oxide and precipitation of nickel chlorides followed by subsequent local acidification. In an extension of the above model to SCC the following work shows that, in a first step, local anodic path corrosion with subsequent oxide breakdown, chloride salt formation and acidification at 288 °C would establish local cathodic reduction of accumulated hydrogen ions inside the crack tip fluid. In a second step, local hydrogen reduction charges and increasing local crack tip strains from increasing crack lengths at given global stresses are time stepwise calculated and related to experimentally determined crack critical cathodic hydrogen charges and fracture strains taken from small scale SSRT tensile tests pieces. As a result, at local hydrogen equilibrium potentials higher than those of nickel in the crack tip solution, hydrogen ion reduction initiates hydrogen crack propagation that is enhanced with increasing global stresses. In accordance with respective experimental literature data it is shown that decreasing chloride and increasing pH levels of the primary bulk water at 288 °C reduce the total crack propagation rates including anodic path corrosion as well as hydrogen cracking. It is also demonstrated that crack propagation rates can be significantly suppressed by hydrogen water chemistry (HWC) that leads to reduction of bulk surface corrosion potentials. As a conclusion the extended SSC-model for nickel supplies quantitative insight into the frequently controversially discussed high temperature SCC mechanisms of a basic alloying element of BWR components.

Photocatalysis and photoelectrocatalysis using (CdS-ZnS)/TiO2 combined photocatalysts

Powdered composite CdS-ZnS photocatalysts of variable composition have been synthesized by a co-precipitation method and were used as photocatalysts to produce hydrogen and as photoelectrocatalysts to produce electricity. Results of catalyst characterization show that composite sulphide photocatalysts form solid solutions and that their band gap energy can be tuned between that of ZnS (3.5eV) and that of CdS (2.3eV) by varying Cd (or Zn) content. The composite materials can photocatalytically produce substantial quantities of molecular hydrogen in the presence of sulphide–sulfite ions as sacrificial electron donors. Photocatalytic performance is significantly improved when small amounts of Pt crystallites are deposited on the photocatalyst surface. The rate of hydrogen production over the Pt-free CdS-ZnS powders depends on Cd (or Zn) content and is generally much higher for the composite materials than for pure CdS or ZnS. Pure semiconductors were found to be very poor photocatalysts under the present experimental conditions. Furthermore, two specific photocatalyst compositions, i.e., 67% and 25% CdS, gave maximum hydrogen production rates. An analogous behavior was observed when the same powders were used to make photoanode electrodes since both the rate of hydrogen ion reduction and the current flow are proportional to the number of photogenerated electrons. Composite CdS-ZnS photocatalysts were also applied by successive ionic layer absorption and reaction on TiO2 films deposited on FTO electrodes. The obtained materials were used as photoanodes in a two-compartment photoelectrocatalysis cell filled with a basic electrolyte and with ethanol as sacrificial electron donor (fuel). The (CdS-ZnS)/TiO2 photoanodes demonstrated a qualitatively similar behavior as CdS-ZnS photocatalysts. Thus 75%CdS–25%ZnS over TiO2 was a better electrocatalyst than 100%CdS over TiO2. When CdS-ZnS photocatalysts were combined with titania, they mainly functioned as visible-light-photosensitizers of this large band-gap semiconductor.

3가크롬 이온의 전착 반응에 용액 산도 및 유기물 첨가제가 미치는 영향 연구

The effect of solution acidity and organic additives, polyethylene glycol (PEG), on the trivalent chromium electroplating was systematically investigated in the view point of electroreduction of trivalent chromium ions and solution stability. It was found that solution acidity controlled at pH 2.5 showed the widest current range for bright electrodeposits in the presence of PEG additives, which reduced the local current intensification at high current densities. Through complex interaction between PEG additives and hydrogen ion, that is, solution acidity, electrode potential was moved in the negative direction in the bulk solution, while it shifted in the positive when electric potential was scanned. In conjunction with electrochemical quartz crystal microbalance (EQCM), it was found that PEG additives had a role in promoting the electron transfer to trivalent chromium ion complexes in bulk solution and their adsorption at the electrode surface as well as interfering with hydrogen ion reduction process below pH 2.5. The PEG additives developed the nodular morphology during electroreduction of trivalent chromium ions with the increase of solution acidity and enhanced its current efficiency by maintaining the consumption of complexant, formic acid, at low speed.

Voltammetric electrodes modified with swollen polyacrylic latex particles

Uniformly sized poly( N-isopropylacrylamide- co-acrylic acid) (NIPA/AA) hydrogel particles were synthesized in order to modify an electrode with a carboxyl group-immobilized one-particle layer. They were spheres with a common diameter under given conditions, which ranged from 0.5 μm to 1.0 μm depending on the pH, ionic concentration and temperature. They were swollen at low salt concentrations, low temperatures and high pH of aqueous suspensions. One particle contained 6.0 × 10 8 carboxyl groups, the concentration of which was ca. 1 M, exhibiting p K a = 5.2. The particles were adsorbed spontaneously on the platinum surface in a one-particle layer with regular arrangement. The particle-adsorbed electrode showed the voltammetric peak for the reduction of hydrogen ions which were dissociated from the carboxylic groups of the adsorbed layer. The amount of the dissociated hydrogen ions per particle was 19% of the loaded amount of carboxyl groups, whereas the non-gelized particles had 3% of the loaded amount. The film worked as a source of supply of hydrogen ions for the electrochemical reduction of 1,4-naphthoquinone. It provided acidic environment of pH 4.5 for the reduction in the neutral solution.

Experimental investigations of cementation of indium

The results on the dynamics of the growth of the precipitate of contactly deposited indium and the variation of their structural characteristics in time, which allow one to reasonably approach the selection of cementation parameters of indium and predict the properties of the obtained powder, are presented. Using a mathematical description of the dynamics of this process allowing for the accompanying reduction of hydrogen ions, the influence of various factors on the rate and structural properties of dendrite precipitates is investigated. The experimental data and results of model calculations yielded an evaluation of the important characteristics of the cementation process, namely, the optimal modes, the distribution of the precipitate by the radii of the vertexes associated with the granulometric composition of the powder, and the density of the location of growing dendrite tips affecting the dendritic structure of the obtained precipitate.

Simultaneous evaluation of the dissociated and undissociated acid concentrations by square wave voltammetry using microelectrodes

The square wave voltammetric response of the reduction of acids of different strength namely, hydrochloric acid, phosphoric acid, lactic acid, acetic acid and sodium dihydrogenophosphate at a platinum microdisk electrode are presented. The voltammograms of HCl and H 2 PO 4 - display a single peak which height increased linearly with concentration. The acids of intermediary strength exhibit voltammograms resulting from the overlapping of two peaks that are assigned to the reduction of hydrogen ions (H +) and of the undissociated acid form (HA). Peaks separation depends on the acid strength and concentration. A numerical deconvolution of voltammograms was performed based on Gaussian peaks fitting. The deconvoluted peak current data for H + were validated towards calibration curves of HCl. The validation of the current data of HA was performed using buffer solutions. The methodology present herein allows to assess simultaneously the concentration of each acid form from a single square wave voltammogram.

2009 W.R. Whitney Award Lecture:Local Hydrogen Generation and Its Impact on Environment-Assisted Cracking and Crevice Corrosion

Abstract An overview is given of the key role for reduction of hydrogen ions and water in determining the local chemistry and electrochemistry in crevices and cracks. Thus, the ability to cathodica...

The possibility for formation of macro-cell corrosion in a liquid with low electrical conductivity

The possibility of electrochemical corrosion of carbon steel at the rate of 3.25 x 10 ―5 A/cm 2 in water was examined under the conditions present during an accidental pipe rupture at the Mihama nuclear power plant: liquid conductivity, 7.5 μS/cm; dissolved oxygen concentration, 5 ppb or less; pH 8.6∼9.3; ferrous ion concentration, 20 ppb or less; temperature, 142 °C. The corrosion rate of iron in a micro-cell with a dissolved oxygen reduction cathode was estimated to be only 1/400 of the preceding rate. On the other hand, that in a micro-cell with a hydrogen ion reduction cathode was estimated to be as high as 1/10 of the preceding rate, that is, 3.25 × 10 ―6 A/cm 2 . Two important factors may have influenced the corrosion rate: the remarkable wall thinning, which must have been the direct cause of the rupture of the pipe, was located close to, and downstream from, an orifice; and, the water temperature was in the range at which carbon steel makes a transition from the active to the passive state. Taking these facts into consideration, it appears possible that micro-cells with different corrosion rates might be generated and integrated into a macro-cell, where the iron dissolution rate might be accelerated to as much as 10 times that of the micro-cell.

Dissociation kinetics at polyacrylic latex-coated electrodes

Polystyrene/poly(acrylic acid) latex particles 0.26 μm in diameter, which were synthesized by emulsion copolymerization of styrene and acrylic acid, were immobilized on the platinum electrode in a uniform film. The film did not block the diffusion current of a ferrocene derivative in the solution. The voltammograms showed the reduction of hydrogen ion, which was supplied not only from the solution but also from the dissociation of carboxyl acid of the adsorbed latex. The peak currents at pH less than 4.5 were proportional to the thickness of the latex film, and were supplied by dissociation from the latex. In contrast, those at pH more than 5.5 were independent of the film thickness, and were controlled by the dissociation kinetics of the carboxyl acid within the first particle layer. Expressions for the voltammetric currents with the CE mechanism were derived theoretically. The theory predicts that the reaction rate constant can be evaluated from the lower deviation from the proportionality of the peak currents to scan rates, as in consistent with the experimental results. The rate constant was by one order smaller than the homogeneous rate constant of acrylic acid. pH-Titration demonstrated the electrostatic interaction of –COO −, like in self-assembled carboxylate films. The average concentration of carboxylate in the latex was ca. 2.7 M. The dissociation was limited to the surface domain of the latex.

Mass transport and effective diffusion coefficient in the reduction of hydrogen ions from aqueous sulfuric acid solutions: Numerical modeling

This work presents results of the numerical solution to a system of equations of material balance and the movement of particles in solution under the influence of the forces of diffusion, migration, and convection, which describe the process of mass transport during the reduction of hydrogen ions at a rotating disk electrode from aqueous sulfuric acid solutions with and without excess supporting electrolyte. Results of the calculations show that the diffusion kinetics of hydrogen ion reduction can be observed only with measurements in dilute (≤10−3 M) sulfuric acid solutions with an excess of indifferent supporting electrolyte. For more acidic solutions it is necessary to take into account the simultaneous diffusion of hydrogen and bisulfate ions. In the study of the regularities of hydrogen ion reduction in sulfuric acid solutions with a sulfate supporting electrolyte, it is necessary to take into account that with excess supporting electrolyte, the limiting current of hydrogen reduction is caused solely by the diffusion of bisulfate ions, but for small concentration ratios of the supporting electrolyte to acid, the influence of migration effects is significant.

Near Ultraviolet and Visible light photoelectrochemical degradation of organic substances producing electricity and hydrogen

A two-compartment, chemically biased photoelectrochemical cell was used to photodegrade several organic substances and produce electricity and hydrogen. The photoanode of the cell was based on commercial nanocrystalline titania, which may be functionalized with CdS to absorb Visible light. The dark cathode was made also of commercial nanocrystalline titania with cast Pt nanoparticles. The cell was run under Near Ultraviolet or Visible radiation and the efficiencies in the two cases have been compared. Short chain-length alcohols and glycerol produced the highest energy yield but water-soluble waste materials are also interesting for the same purpose. The overall efficiency of cells made by CdS-functionalized titania was higher than those made of pure titania. However, larger currents were obtained with pure TiO 2 under Near Ultraviolet excitation. Under anaerobic conditions, molecular hydrogen can be produced at the dark cathode by the reduction of hydrogen ions generated at the photoanode.

The convection-driven non-additivity of the faradaic currents for the parallel reduction of some metal and hydrogen cations at the mercury electrode

An atypical example of the effect of the self-induced convection on the morphology of current-potential responses was described, for the case of the parallel electroreduction of some metal cations (Cd 2+, Cu 2+, Zn 2+ and Eu 3+) and H + ions at the mercury electrode. Separation of the individual faradaic contributions from the metal ions and hydrogen ions reduction, made with the double potential-step chronocoulometry, and based on the difference between the rates of these processes, allowed us to find that the total faradaic current exhibits negative or positive deviations from the sum of individual faradaic currents. In order to diagnose the origin of this anomaly, the series of experiments for various acid concentrations, electrolysis times and the electrode types/geometries, including the hanging mercury drop and the mercury film electrodes, were performed. The results obtained indicated that the observed anomalies are due not to the surface blocking or latent limiting currents, but due to a rather novel mechanism that involves convective instabilities which accompany the hydrogen evolution reaction. The resulting change of the concentration distribution of all species involved in the electrode process appropriately changes the individual contributions from the faradaic currents. These studies show one more role of convection in electrochemical systems.

A mathematical model for crevice corrosion under porous deposits

A model has been developed to investigate the corrosion of steels in a thin, narrow crevice formed between the metal surface and an oxygen-permeable, porous deposit. A thin electrolyte layer exists within the deposit, due to geochemical fluids dripping onto a deposit-covered surface or due to the adsorption of moisture by a hygroscopic deposit. Mass transfer by diffusion and ion migration is considered in both the electrolyte films inside and outside of the crevice. The main reactions considered are the anodic dissolution of the alloy substrate, hydrolysis of the alloying element cations, dissociation of water, and the cathodic reduction of oxygen, hydrogen ion, and water. Special attention has been given to the role of parameters connected with the porous layer (porosity, tortuosity, and the layer thickness) on the rate of crevice corrosion. It is shown that the cavity acts as an ‘electrochemical amplifier’ from the point of view of the concentration of aggressive anions that leads to increasing of corrosion rate and to a higher probability of pit nucleation within the crevice.

Modeling the Effect of Chloride Content on Hydrogen Sulfide Corrosion of Pure Iron by Coupling of Phase and Polarization Behavior

Abstract Localized corrosion of higher alloyed steels has frequently been shown to produce locally aggressive solutions with low pH levels in crevices and pits. It also has been established that such solutions can serve to initiate and propagate stress corrosion cracking. The present model aims at a basic understanding of the time-dependent local acidification process and, in a first approach, uses pure iron as a model metal. The model couples the anodic polarization resistances to the precipitated equilibrium masses of iron disulfide (FeS2), which in a “closed loop” time stepwise procedure are calculated from the solute concentrations in a diffusion boundary layer. With the cathodic process controlled by hydrogen ion reduction, the precipitation of FeS2 enforces local pH reductions at the anodic site depending on the total concentrations of HS−, Fe++, and H+ in the assumed diffusion layer. In the present work, the effects of chlorides on ion migration, sulfide solubility, anodic polarization resistances,...

Formation mechanism and structure of nickel-molybdenum-boron chemical-catalytic coatings

Effect of molybdate-ions on the kinetics of partial reactions of dimethylamine-borane oxidation and nickel-and molybdate-ions reduction in the process of their chemical-catalytic reduction during the Ni-Mo-B-coatings deposition is studied. Molybdenum is deposited as metal only in the codeposition with nickel, yielding amorphous alloys. Adding of low concentration of the molybdate-ions to the nickel-plating solution increases the hydrogen evolution and alloy deposition rates as a result of the accelerating of dimethylamine-borane heterogeneous hydrolysis. At high molybdate-ion concentrations in the solution, a denser film of the molybdate reduction intermediate products forms at the electrode surface; this decreases the system’s catalytic activity as regards the dimethylamine-borane heterogeneous hydrolysis and thus decreases the hydrogen and nickel ions reduction rates.

Effective thickness of the diffusion layer during hydrogen ion reduction in aqueous hydrochloric acid solutions

The process of mass transport during hydrogen ion reduction in aqueous hydrochloric acid solutions is examined both with and without excess supporting electrolyte. The study of this process is based on a numerical solution to a system of equations of material balance and the movement of particles in solution under the influence of forces for diffusion, migration, and convection. The homogeneous chemical reaction of water dissociation is also taken into account. The results of calculations show that a diffusion layer forms near the electrode during the passage of current in these solutions and that the effective thickness of this layer is the same at any instant for all particles participating in mass transport in solution in spite of differences in their diffusion coefficients. The value of the diffusion coefficient measured in these multicomponent solutions by the methods of chronopotentiometry and rotating disk electrode should differ little from that of hydrogen ions in spite of the fact that other particles with different diffusion coefficients participate in the mass transport.

Investigation of Formation Process of the Chrome-free Passivation Film of Electrodeposited Zinc

The feasibility was investigated to substitute chrome-free passivation treatment of electrodeposited zinc in a titanium bath for chromate passivation treatment. The formation mechanism of the chrome-free passivation film was further analyzed. The surface morphologies and the elemental compositions of the treated samples with varied immersion times were observed by scanning electron microscopy (SEM) and determined by energy dispersion spectrometry (EDS), respectively. The electrode potential of the sample surface was recorded in the film formation process. The changes of the electrode potential are in accordance with that of SEM and EDS of the sample surface. The results of X-ray photoelectron spectroscopy (XPS) show the chrome-free passivation film composed of ZnO, SiO2, TiO2, Zn4Si2O7(OH)2, and SrF2. The anode zinc dissolution and the local pH value increase due to the cathode hydrogen ion reduction process result in the formation of the chrome-free passivation film. The macro-images of the chrome-free passivation films formed on electrodeposited zinc show that the color of the film changes from blue to iridescence with the increase of the immersion times.

Nacre coatings deposited by electrophoresis on Ti6Al4V substrates

Crack-free nacre coatings on titanium alloys were produced by electrophoretic deposition in a nacre/ethanol suspension with or without a hydrochloric acid (HCl) additive. The microstructure and morphology of coatings were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The deposition yield of nacre powders was determined by weighting the dried deposits. The results show that the HCl additive has no obvious effects on the crystalline phase of nacre coatings. The deposition yield of nacre powders increases with adding acid additives, prolonging deposition time, and improving applied voltage. A uniform and glue-like nacre coating is deposited in a suspension with the HCl additive via a dissolution–precipitation reaction. After the HCl additive is added into a nacre/ethanol suspension, calcium ions are released from nacre powder surfaces, and move toward the cathode within an electric field. The local concentrations of hydroxide ions and carbonate ions increase due to the reduction of hydrogen ions at the cathode surface. Calcium ions react with carbonate ions to form calcium carbonate as the ionic activity product exceeds its thermodynamic solubility product, and re-precipitates on the active sites of nacre powder surfaces.