Der Einfluß des elektrochemischen Metallpolierens auf die Wasserstoffüberspannung

An experimental study of hydrogen overpotential on electropolished and non-polished metals with low, average and high overvoltage values has been made. The data in the literature on this subject are poor and contradictory. Platinum, iron, nickel, aluminum, silver, copper, lead and zink were used as samples in the investigation. It has been established that electropolishing causes an increase of hydrogen overpotential on metals with low overpotential and a decrease on metals with average and high overvoltage values. A qualitative explanation is given.     

Temperature dependence of hydrogen overvoltage on nickel and iron in acid solution

The temperature dependence of hydrogen overvoltage on mechanically and chemically polished nickel electrodes, on iron armco, and iron of high purity in 0.25 M H₂SO₄ are studied in the interval of temperatures 298–278 K. It is established that the influence of temperature on the slope of Tafel line depends essentially on the type of electrodes. The apparent energy of activationE and pre-exponential factorB are determined. The results show an important role of the electrode surface treatment and purity of the metal in the determination of energetic parameters of the hydrogen evolution reaction. The most striking result is that in the case of nickel electrodes with mechanically polished surfaceE increases andB decreases with the increase of overvoltage. Some aspects of nonclassical behavior of electrodes studied are discussed. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth.     

Alloy electrodes with high hydrogen overvoltage for analytical use in voltammetry. Some preliminary results

Liquid mercury and liquid diluted mercury amalgams have been the major electrode systems employed in voltammetry and related methods. This is mainly due to their high overvoltage to hydrogen, which enables the determination of heavy metals (zinc, nickel, cobalt, etc.) and other species with high negative half-wave potentials; the toxicity of mercury and liquid diluted mercury leads to ever increasing restrictions in their use. The use of such systems may even be forbidden in the future, at least in online systems for work in the field. Recent work, carried out in our laboratory, has demonstrated that a non-toxic solid dental amalgam may be used as the electrode material, conveniently replacing mercury. An extension of this work has shown that electrode materials comprising a metal or a compound with low hydrogen overvoltage change their hydrogen overvoltage properties substantially when contaminated with even small amounts of metals or compounds which show high hydrogen overvoltage. This extends greatly the range of potentially available electrode systems and thereby analytical possibilities of voltammetry. This new discovery also makes it possible to produce solid electrodes that have high overvoltage to hydrogen without any use of mercury.     

贮氢合金电极的活化方法和作用机理研究

比较研究了采用电化学方法、ＫＢＨ４还原，ＫＯＨ刻蚀及ＫＯＨ＋ＫＢＨ４联合作用对Ｍｍ（ＮｉＣｏＭｎＡｌ）５型贮氢电极的活化作用，发现采用浓热ＫＯＨ处理的电极可以实现快速充分的活化，且具有放电电压低、稳定容量高及操作简便的特点．对活化过程的作用机理研究表明，ＫＯＨ活化主要是通过溶解反应使稀土和镍元素富集生成有利于吸氢反应的表面组成．ＫＢＨ４及电化学活化方法则是利用反应产生的活性氢裂解合金颗粒，生成高活性的新鲜表面和晶体缺陷     

The states of hydrogen adsorbed on the surface of skeleton nickel

The experimental data on hydrogen adsorption on skeleton nickel were used to construct the pK spectrum of atomic hydrogen on this surface. The pK spectrum obtained corresponded to the presence of three adsorption centers on the surface of skeleton nickel. A chemical model of hydrogen adsorption on the surface of skeleton nickel was suggested.     

Mesoporous Nickel–Alumina Catalysts for Hydrogen Production by Steam Reforming of Liquefied Natural Gas (LNG)

Recent progress on the mesoporous nickel–alumina catalysts for hydrogen production by steam reforming of liquefied natural gas (LNG) was reported in this review. A number of mesoporous nickel–alumina composite catalysts were prepared by a single-step surfactant-templating method using cationic, anionic, and non-ionic surfactant as structure-directing agents for use in hydrogen production by steam reforming of LNG. For comparison, nickel catalysts supported on mesoporous aluminas were also prepared by an impregnation method. The effect of preparation method and surfactant identity on physicochemical properties and catalytic activities of mesoporous nickel–alumina catalysts in the steam reforming of LNG was investigated. Regardless of preparation method and surfactant identity, nickel oxide species were finely dispersed on the surface of mesoporous nickel–alumina catalysts through the formation of surface nickel aluminate phase. However, nickel dispersion and nickel surface area of mesoporous nickel–alumina catalysts were strongly affected by the preparation method and surfactant identity. It was found that nickel surface area of mesoporous nickel–alumina catalyst served as one of the important factors determining the catalytic performance in hydrogen production by steam reforming of LNG. Among the catalysts tested, a mesoporous nickel–alumina composite catalyst prepared by a single-step non-ionic surfactant-templating method exhibited the best catalytic performance due to its highest nickel surface area.     

Hydrogen adsorption on nickel (100) single-crystal face. A Monte Carlo study of the equilibrium and kinetics

We propose a model of the dissociative adsorption of hydrogen on nickel single-crystal face. In this model, we treat the Ni(100) surface as a strongly correlated energetically heterogeneous surface, because the density functional theory (DFT) studies indicate that hydrogen atoms may adsorb either on hollow sites (energetically more favorable, binding energy 48 kJ/mol H) or bridge sites with the binding energy less by 11 kJ/mol H. The essential assumption of the proposed model is that the dissociation of the hydrogen molecule is possible only over the topmost Ni atom, and the resulting H atoms may adsorb either on two free hollow sites (but the adjacent bridge sites must be free) or two bridge sites (the adjacent hollow sites must be free). If the above condition is not fulfilled, then the dissociation and adsorption are impossible. The second assumption is that the rate (probability) of the associative desorption is limited by the rate of diffusion of H atoms on the surface. This is because the two H atoms desorb, giving an H2 molecule, only when they meet on two adjacent hollow-bridge sites. Our model recovers very well the behavior of the experimental equilibrium adsorption isotherms as well as kinetic isotherms. As a result, we stated that hydrogen atoms are not completely free on the surface, but they cannot also be considered localized at room and elevated temperatures. Additionally, while analyzing the kinetic adsorption isotherms, we stated that the rate-limiting step during the dissociative adsorption of H2 is the disintegration of the activated complex and the subsequent adsorption of hydrogen atoms.     

The thermodynamic characteristics of processes in Raney nickel surface layers with the participation of adsorbed hydrogen forms

Equilibria between adsorbed hydrogen forms on the surface of Raney nickel in aqueous solutions were studied by the potentiometric and adsorption-calorimetric methods. The establishment of equilibria between adsorbate forms was proved experimentally. The model of a surface with discrete inhomogeneity was used to determine the standard thermodynamic characteristics of surface equilibria and adsorption of particular hydrogen adsorption forms. The influence of pH of the bulk phase on the thermodynamic characteristics of adsorption of hydrogen on the surface of Raney nickel caused redistribution of adsorbed hydrogen forms.     

Using solvents to control hydrogen adsorption on skeletal nickel

The results from adsorption-calorimetric studies of hydrogen adsorption on skeletal nickel are generalized. The thermodynamic characteristics of adsorbed hydrogen are calculated according to the model of an ideal surface with discrete heterogeneity. It is shown that the states of surface layers in solutions, formed upon hydrogen adsorption on skeletal and porous nickel, depend on the nature and composition of the solvent. Based on the resulting data, the possibility of using a solvent to control adsorption in a skeletal nickel-hydrogen system is confirmed.     

The heats of hydrogen adsorption on Raney nickel from aqueous-organic solvents with acid and base admixtures

The heats of hydrogen adsorption on porous nickel from aqueous solutions of dimethylformamide containing acetic acid and sodium hydroxide admixtures were measured by adsorption calorimetry. The introduction of acid or alkaline admixtures changed both the amount of hydrogen adsorbed on the surface of porous nickel and the character of the dependences of the heats of adsorption on this amount. The composition of solvents influenced adsorption because of the quantitative redistribution of adsorption values among various hydrogen adsorption forms bound by the active centers of the surface of nickel determined by changes in medium basicity.     

Electrochemical Hydrogen Evolution at a Single-Crystal Zirconium Face in Sulfuric Acid Solutions

The electrochemical behavior of a zirconium electrode in 1 N H₂SO₄ is studied at various values of overvoltage, temperature, pH, and concentration of a surface-active substance. A mechanism of hydrogen evolution on the partly reduced surface of a zirconium single crystal is put forth. The assumption that zirconium readily forms zirconium hydride, which considerably alters the surface electrochemical properties, is confirmed. The hydrogen absorption on the single crystal results in the emergence of cracks on the metal surface in a certain crystallographic orientation. X-ray diffraction analysis is used to determine the index of the working surface of the zirconium single crystal and calculate the crystal lattice parameters.     

Reaction of [2-(SiH3)C6H4]2SiH2 with Ni(Et2PCH2CH2PEt2)(PEt3)2: characterization of eta2-(Si-H)Ni and NiIV-H complexes

The reaction of (2-SiH3C6H4)2SiH2 with Ni(Et2PCH2CH2PEt2)(PEt3)2 afforded a new silylnickel complex, which, in the solid state, was determined to be a bis(silyl)eta2-(Si-H)nickel complex, the first example of eta2-(Si-H)nickel complex by single-crystal X-ray analysis. Variable-temperature NMR spectroscopy revealed fluxional behavior of the complex in solution; at room temperature, exchange of five hydrogens (two SiH2 and one hydrogen bound to nickel) was observed, while at -80 degrees C the exchange of hydrogens appeared frozen to adopt a tris(silyl)(hydrido)nickel(IV) structure, which was confirmed by theoretical calculation. The latter complex is the first example of hydridonickel(IV) complex.     

Untersuchungen an Nickel-Zeolith-Trägerkatalysatoren. I. Herstellung und Charakterisierung von Nickel-Zeolith-Trägerkatalysatoren

By means of cation exchange nickel zeolites of the types A, X and Y were prepared with different (0.5–12.5% of weight) nickel, contents. Nickel zeolites of the A type up to 14% exchange and zeolites of the X type up to 27% exchange do not show changes in structure. Nickel zeolite catalysts were prepared by reduction of the nickel zeolites with hydrogen. Analyses of nickel metal in these catalysts showed that only part of the nickel cations is reduced. By means of hydrogen chemisorption it could be proved that the metallic nickel does not exist in atomic dispersion and is deposited on the external surface as well as inside the pores.     

Influence of the Oxide Content in the Catalytic Power of Raney Nickel in Hydrogen Generation

The influence of oxides in the hydrogen evolution on Raney nickel electrocatalysts was characterized by electrochemical impedance measurements. In addition, these materials show competitive overpotentials for hydrogen evolution with a modified Watts bath as a binder for the Raney nickel. The optimum result was ?190?mV of overpotential at 100?mA?cm^?2. Oxygen in the Raney Ni catalyst affects its electroactivity toward hydrogen evolution. The source of oxygen is related to the presence of chloride ions in the modified Watts bath. A Watts bath binds Raney Ni particles to the surface of the catalysts and chloride regulates the oxygen content in the nickel binder during electrodeposition. High oxygen content increases the hydrogen evolution overpotential of the electrode. The electroactivity of the synthesized porous coatings was evaluated by polarization curves and impedance plots. In addition, surface characterization by X-ray diffraction, field emission–scanning electron microscopy equipped with energy-dispersive analysis, and X-ray photoelectron spectroscopy is reported.     

镍硫活性阴极的催化活性及其机理探讨

镍硫活性阴极的催化活性及其机理探讨孙弘（沈阳教育学院化学系沈阳１１００１５）张蕴珊（东北大学化学系沈阳１１０００６）关键词镍硫活性阴极催化活性中图分类号６４６．５前言研制廉价易得、对析氢催化活性高的电极材料以降低能耗，对氢碱工业具有深远的意义。近年来...     

Effects of the nature and composition of the solvent on the thermodynamic characteristics of the individual forms of hydrogen adsorbed on the surface of porous nickel

The effects of the nature and composition of solvents on the thermodynamic characteristics of the adsorption states of hydrogen on nickel were studied. The adsorption can be described in terms of the thermodynamic model of a surface with a discrete nonhomogeneity for three individual forms of adsorbed hydrogen. The thermodynamic characteristics of the individual forms of hydrogen adsorbed on porous nickel from aqueous solutions of sodium hydroxide, dimethylformamide, methanol, and ethanol were determined.     

Studying the process of ionization of hydrogen in conditions of its forced delivery to a porous nickel oxide electrode

The hydrogen ionization process is studied experimentally on an industrial sintered nickel oxide electrode in models of sealed nickel-metal hydride batteries. It is shown that the hydrogen ionization rates that are reached during overcharge by high current densities in conditions of forced gas delivery into the electrode pores (up to 40 mA cm^?2) exceed the self-discharge rate of a nickel-hydrogen battery by two orders of magnitude. Up to 70% of hydrogen delivered into the compact assembly block undergoes ionization during forced charge of models of sealed nickel-metal hydride batteries with a closed hydrogen cycle. Two independent methods (potentiostatic and manometric) are used to determine the relationship between rates of hydrogen ionization with the degree of the electrode filling with gas and perform estimation of the process intensity at a unit reaction surface. It is established that, in conditions of forced gas delivery, practically all the hydrogen oxidation current is generated at the surface of the nickel oxide electrode beneath thin films of an electrolyte solution at the rate of 4–5 mA cm^?2. It is shown that the hydrogen oxidation rate on a nickel oxide electrode filled in part by gas is independent of the electrode potential, probably because of a tangible contribution made by diffusion limitations to the overall hampering of the process.     

Voltammetry of basal plane platinum electrodes in acetonitrile electrolytes: effect of the presence of water

The first part of this report studies the electrochemical properties of single-crystal platinum electrodes in acetonitrile electrolytes by means of cyclic voltammetry. Potential difference infrared spectroscopy in conjunction with linear voltammetry was used to obtain a molecular-level picture of this interface. The second part of this report studies the hydrogen evolution and the hydrogen oxidation reactions on the three low-index faces of Pt electrodes in acetonitrile electrolytes. The data (CVs and IR spectra) strongly suggest that acetonitrile and CN(-) molecules are adsorbed on single-crystal platinum electrodes in the range of -1.5 to 0.3 V versus Ag/AgCl. Those species block part of the adsorption sites for hydrogen adatoms, and they decompose on the surface in the presence of water. The nature of the cation and the presence of water strongly affect the onset of acetonitrile electrolysis and the kinetics and stability of the adsorbed species on the electrode. Finally, the hydrogen evolution and the hydrogen oxidation reactions on platinum single-crystal surfaces in acetonitrile electrolytes are strongly affected by the surface-energy state of Pt electrodes.     

A Structural Study of the Homogeneity Domain of LaNi5

LaNi₅ is a very important intermetallic compound for hydrogen storage applications. Its homogeneity range at 1200°C has been investigated by single-crystal X-ray diffraction, electron probe microanalysis, and mass density measurements. At the nickel-rich end the hexagonal structure (CaCu₅ type) extends to the composition LaNi_5.45. The excess of nickel is accommodated by random substitutions of lanthanum atoms by nickel dumbbells and by displacements of nickel atoms which are presumably correlated with the La atom substitutions. Interatomic distances suggest that the Ni atom displacements occur in directions toward vacant La atom sites, i.e., toward the center of Ni dumbbells. At the nickel-poor end the structure extends to the composition LaNi_4.88. The excess of lanthanum is presumably accommodated by the simultaneous occurrence of lanthanum atoms and vacancies on nickel atom sites. Both models are consistent with mass density and electron probe microanalysis measurements. Hydrogenation thermodynamic properties have been measured as a function of composition.     

A study of the effect of some pollutant gases on cathodes used in membrane-covered amperometric oxygen detectors

The effects of various gaseous pollutants on the electrochemical activity of materials used as cathodes for membrane-covered amperometric oxygen detectors are described. It is shown that gold and platinum cathodes are not unduly affected by concentrations of sulphur dioxide and chlorine many times greater than those likely to be encountered in test solutions, and that a gold cathode is also unaffected by hydrogen sulphide. A platinum cathode is rapidly and significantly poisoned on contact with hydrogen sulphide; an analysis of the fall in the rate of oxygen reduction as a function of time indicates that the poisoning occurs by the blocking of surface sites by sulphide. The effect of hydrogen sulphide on silver, nickel and nickel sulphide electrodes is also reported. Of these materials, only nickel sulphide is an effective electrocatalyst for oxygen reduction in the presence of sulphide.