Plasma-sprayed nickel cathode coatings for hydrogen evolution in alkaline electrolytes

Hydrogen evolution cathodes with plasma-sprayed nickel coatings were much more efficient in alkaline electrolytes than either uncoated cathodes or cathodes with porous sintered nickel coatings. This efficiency improvement could not be attributed to either superior coating morphology or increased surface area. The degree of coating oxidation appeared to be the main factor influencing the hydrogen evolution overpotentials at either the plasma-sprayed or sintered nickel cathode coatings studied. Highly-oxidized nickel surfaces produced much lower Tafel slopes than similar unoxidized surfaces. Plasma-sprayed nickel cathode coatings made with fine, high surface area nickel powder produced hydrogen evolution overpotentials in the range 0.10–0.14 V.     

Evaluation of zinc sulphate electrolytes containing certain impurities and additives by cyclic voltammetry

The polarization characteristics of acid zinc sulphate electrolytes containing various amounts of germanium and cobalt were examined by cyclic voltammetry. The effects of zinc and acid concentration, temperature, and surface preparation were also investigated. Small concentrations of impurities are shown to cause measurable changes in polarization behaviour. Levels as low as 0.02 mgl^–1 Ge and 0.1 mgl^–1 Co can be detected using this technique. The actual mechanism of impurity behaviour is more clearly delineated using this technique and evaluation of the data from these tests indicate that germanium and cobalt form local galvanic cells. The results of these short-term tests are shown to correlate with classical long-term efficiency tests. The deposit morphologies obtained for short-time cathodic cycles were also studied using scanning electron microscopy.     

Electrochemical and photoelectrochemical behaviour of passivated niobium electrodes during hydrogen evolution

The electrochemical and photoelectrochemical behavior of niobium electrodes passivated in 0.5 M H₂SO₄ and 1 M HNO₃ has been investigated. High intensity pulse lasers were used as light sources. This technique allows photoelectrochemical measurements with light wavelengths smaller than the band gap of the semiconducting passive film. The donor concentration and the flat band potential of the passive films were calculated from capacity measurements. The effect of cathodic hydrogen evolution on the behaviour of the oxide film formed was found to depend on the time of the cathodic treatment of the electrode. The results showed that the behaviour of the passive film formed on niobium in nitric acid is different from that formed in sulphuric acid. The calculated donor concentrations and the extrapolated flat band potentials indicate that the nature of the passive film depends on the formation medium. The adsorption of hydrogen on the passivated Nb-electrode up to a time limit of 1 ms could be traced using photocharge measurements with excitation energies less than the band gap energy of the semiconducing oxide film.     

碱性电解水析氢中的异质结构催化剂

碱性环境下单相金属催化剂的电催化产氢的动力学过程普遍缓慢远不及其在酸性条件,且存在易腐蚀等问题。近期很多异质结构催化剂被报导在碱性条件下表现出优异的析氢性能或长时间的耐用性,其中一些非贵金属催化剂达到了与贵金属基催化剂类似的高催化活性,为碱性条件下产氢催化剂的设计与开发提供了新思路。首先,介绍了异质结构相较于单一材料在产氢催化中的优势,并补充说明了碱性产氢理论相关背景。然后,追溯异质结构在碱性产氢催化剂中的研究路径,主要介绍了异质结构催化剂中极其重要且报导众多的过渡金属氢氧化物基、氧化物基以及硫化物基的异质结构催化剂,通过实例展示异质结构催化剂的制备方法、表征策略以及相应的设计思路。最后,分析了异质结构催化剂在固有活性比较中的困难并对异质结构催化机理的未来研究进行了展望。     

碱性电解水析氢中的异质结构催化剂

碱性条件下单相金属催化剂的电催化产氢动力学过程普遍缓慢,远不及其在酸性条件下的析氢性能,且存在易腐蚀等问题.近期,很多异质结构催化剂在碱性条件下表现出优异的析氢性能或长时间耐用性.其中,一些非贵金属催化剂达到了与贵金属基催化剂类似的高催化活性,为碱性条件下产氢催化剂的设计与开发提供了新思路.首先,介绍了异质结构催化剂较...     

Zinc electrowinning from acidic sulphate solutions Part II: Effects of triethylbenzylammonium chloride

The effects of triethylbenzylammonium chloride (TEBACl) on the electrowinning of zinc from acidic sulfate solutions have been studied in the presence and absence of antimony(iii). The factors considered included the current efficiency (CE), power consumption, polarisation behaviour, and the crystallographic orientations and surface morphology of the deposits. Compared with the traditional industrial additive, glue, the addition of TEBACl increased CE, reduced power consumption and improved the surface morphology. Maximum CE and minimum power consumption were obtained at 2mgdm–3 TEBACl and 0.01mgdm–3 Sb(iii). The exchange current density, Tafel slope and transfer coefficient were determined to elucidate the nature of the electrode reactions involved.     

Reaction mechanism of anodic oxygen evolution on nickel in sulphate solutions

The anodic polarization curve of the oxygen electrode was examined on nickel in sulphate solutions of various pH values ranging from 0 to 14. It was found that oxygen evolution proceeds in accordance with two different reaction kinetics depending upon the pH value of the solution and the magnitude of the anode current density.In acid solution and in alkaline solution in a relatively high current-density region, the anodic oxidation of water molecule through the rate-determining step H₂O → OH(ads) + H⁺ + e is suggested as the reaction mechanism. In alkaline solution in a relatively low current-density region the oxygen is evolved from OH⁻ ion according probably to OH⁻ → OH(ads) + e, OH(ads) + OH⁻ → O(ads) + H₂O + e, and 20(ads) → O₂, with the second step determining the over-all reaction rate. The transition between oxygen evolution from H₂O and that from OH⁻ ion comes about at pH around 11 and is caused by the limiting diffusion current of OH⁻ ion.     

Zinc electrowinning from acidic sulphate solutions. Part III: Effects of quaternary ammonium bromides

The effects of the organic additives cetyltrimethylammonium bromide (CTABr) and tetrabutyl ammonium bromide (TBABr) on the electrowinning of zinc from acidic sulphate solutions were studied in the presence and absence of trace amounts of antimony(iii). The results indicated that CTABr has similar properties to the commonly used industrial additive glue with respect to current efficiency, power consumption, polarization behaviour, and the crystallographic orientation and surface morphology of the zinc deposits. TBABr was generally less useful with respect to all these properties. Voltammetric studies indicate that polarisation for zinc electrodeposition decreased in the order CTABr > glue > TBABr. The nature of the electrode reactions were investigated through measurements of exchange current densities, Tafel slopes and transfer coefficients.     

The simultaneous deposition of nickel and hydrogen on vitreous carbon

Linear sweep voltammograms for the dissolution of electrodeposited nickel indicate that a mixture of two nickel phases is usually deposited. These two phases have been identified as hydrogen-rich β-nickel and the solid solution α-nickel. The anodic charges obtained for each of these have been used in the analysis of the cathodic transient. The partial transient for α-nickel appears to obey the laws for three-dimensional growth and progressive nucleation. In the partial transient for β-nickel mass transfer of hydrogen ions becomes a rate-determining factor. The latter appears to be responsible for the maxima in the cathodic transients.     

Effects of metallic and D2EHPA impurities on nickel electrowinning from aqueous sulphate baths

The presence of metallic and organic solvent impurities in pregnant electrolyte during hydrometallurgical processing causes problems in nickel electrowinning. To overcome these problems, a study on the combined effects of metallic and D2EHPA impurities, on nickel electrodeposition has been carried out. The effects of such impurities on deposit physical appearance, current efficiency, deposit contamination, crystallographic orientation and deposit morphology are discussed. Based on the experimental data and observations, it is possible to achieve smooth and perfect nickel sheet with reasonable current efficiency and purity from the contaminated leach liquors of nickel bearing raw materials being processed in the Regional Research Laboratory, Bhubaneswar. Moreover, the economy of the nickel electrowinning process can be improved by careful selection of experimental conditions.     

Influence of a perfluorinated surfactant on the mechanism of zinc deposition in acidic electrolytes

The influence of the non-ionic surfactant Forafac F1110 on the kinetics of zinc deposition in sulfate or chloride solutions is investigated by voltammetry and impedance spectroscopy. From a discussion of the results in terms of a reaction model, it is shown that the additive produces a significant inhibition of the corrosion process. In addition and in a specific way for each electrolyte, the additive (i) inhibits the different steps of charge transfer leading to the zinc deposit and (ii) modifies the kinetic parameters of the slow reactions involved in the formation and destruction of the active sites for zinc deposition.     

析氢对电沉积镍枝晶生长的影响

采用点电极电沉积的方法,在环形电解池中用自行设计的试验装置研究了不同电压和NiSO4质量浓度时,析氢对电沉积金属镍枝晶二维生长行为的影响。研究发现,析氢对沉积产物的形貌影响显著,氢气的大量析出有利于枝晶产生分枝,使沉积物的形貌趋于致密。     

Electrochemical behaviour of manganese: Dissolution,deposition, hydrogen evolution

Manganese dissolution and deposition and hydrogen evolution at manganese electrodes in aqueous chloride and sulphate solutions have been studied at room temperature (22–23°C) by means of a slow galvanostatic technique. The steady-state dissolution and deposition (when not affected by concentration polarization) are found to obey mutually symmetrical and pH-independent Tafel lines of numerical slope 2·303 RT/2F. The results give a standard exchange current (J₀ = i₀/ a) of 0·022 A/cm² for the Mn/Mn_aq²⁺ electrode at the temperature concerned. The hydrogen evolution reaction is found to be under diffusion control at the corrosion potential of manganese. At somewhat lower potentials (and higher rates), it gives a pH-independent Tafel line of slope −2·303 2RT/F for the activation-controlled reduction of water. Comparisons are made with corresponding data for the other late 3d metals.     

Smooth Raney nickel coatings for cathodic hydrogen evolution by chemical gas phase reaction of nickel electrode surfaces

Two different processes to prepare smooth* Raney nickel coatings are investigated. Both are based on preparing a precursor coating by gas-phase reaction of nickel at temperatures of around 400°C. Sherardizing of nickel electrodes, that is, reaction with zinc vapour, leads to formation of the -phase of Ni–Zn alloy with the approximate composition of 75 to 85wt% Zn (balance: Ni), and gas-phase sulfidizing of nickel electrodes with hydrogen sulfide produces nickel sulfide coatings composed of the phases Ni3S2, Ni7S6 and NiS. Both types of coating are transformed in situ, the first by caustic leaching and the second during cathodic hydrogen evolution by relatively slow cathodic reduction into smooth, almost closed nanoporous Raney nickel coatings. The comparison of the catalysts from the two different methods reveals the superiority of the second. The hydrogen evolution overpotential is lowest and, during more than 3000h of continuous operation, the catalyst does not deteriorate. Electrodeposited nickel sulfide gives a poorer and less stable RN catalyst than gas phase sulfidized nickel sulfide.     

Comparative study of copper electrodeposition from sulphate acidic electrolytes in the presence of IT-85 and of its components

The effect of a new additive (IT-85) representing a mixture of triethyl-benzyl-ammonium chloride (TEBA) and hydroxyethylated-2-butyne-l,4-diol (Ferasine) on the kinetics of copper electrodeposition from sulphate acidic electrolytes, as well as on the morphology and structure of copper deposits was investigated and compared with those exerted by its two components, TEBA and Ferasine. Quasi-steady state hydrodynamic voltammetry at a rotating-disc electrode and electrochemical impedance spectroscopy were performed in order to obtain information about the kinetics of the cathodic process. SEM and X-ray diffraction analysis were used to examine the morphology and the structure of copper deposits. The kinetic parameters (_c, k₀) obtained by both Tafel and Koutecky-Levich interpretations showed that all tested organic additives have an inhibiting effect on copper electrodeposition. Unlike IT-85 or Ferasine, TEBA acts only as a blocking agent in the copper discharge process, without changing the reaction pathway corresponding to the absence of additives. Comparison of the inhibiting effects exerted by IT-85 and its components on the electrodeposition process pointed to the existence of a beneficial complementarity of TEBA and Ferasine when they are used in mixture.     

Dispersion deposition of metal — Particle composites and the evaluation of dispersion deposited nickel — Lanthanum nickelate electrocatalyst for hydrogen evolution

A method for the preparation of high surface area coatings and its application towards fabrication of prospective composite electrocatalysts for hydrogen evolution is proposed. Exploratory studies with such a composite, (Ni/LaNiO₃), as a hydrogen electrode in alkaline solutions indicate that it is a more active electrocatalyst than sintered or electrodeposited nickel. The electrocatalytic properties were found to be a strong function of the deposition parameters as well as of the history of the oxide powder.     

Morphology, structure and magnetic properties of cobalt–nickel films obtained from acidic electrolytes containing glycine

This paper focuses on the development and optimization of electroplated cobalt–nickel (CoNi) alloys for use in biomedical microdevices. CoNi films were electrodeposited from glycine-containing electrolyte solutions at acidic pH. The influence of pH (2.5–5), temperature (55 and 80 °C), current density (from −5 to −40 mA cm⁻²), glycine concentration (0.5 and 1 mol dm⁻³) and the nature of the metal salts (chlorides or sulphates) on the composition and the magnetic properties of the films were systematically analyzed. The cobalt content varied between 50 and 83 wt% depending on the applied conditions. As a result, deposits showed variable morphologies, different structures (either hexagonal close-packed (hcp) or mixed hcp and face-centered cubic phases) and tunable magnetic properties, ranging from semi-hard (18.51 kA m⁻¹, i.e. 233 Oe) to very soft (1.43 kA m⁻¹, i.e. 18 Oe). To understand the role of glycine in this system, a comparison of the electrochemical processes, and the structural and magnetic properties is made for samples produced in glycine-containing and glycine-free baths.     

The effect of nickel on the mechanism of the initial stages of zinc electrowinning from sulphate electrolytes. Part II. Investigations on aluminium cathodes alloyed with iron impurities

The effect of the alloying element Fe on the electrochemical behaviour of Al cathodes during the initial stages of zinc electrowinning was studied, using scanning electron microscopy, cyclic voltammetry, atomic absorption and X-ray microprobe analysis techniques. It is shown that underpotentially deposited zinc submonolayer inhibits the discharge of hydrogen ions onto Fe aggregates — alloying element.