Solid State Phenomena Vol. 228

Abstract: The Ni+Mo and Ni+W nanocomposite coatings were prepared by electrodeposition under the galvanostatic conditions (j_dep = -300 mA cm^-2) from the nickel bath containing nanopowders of molybdenum (<100 nm) or tungsten (<150 nm). Kinetics of hydrogen evolution reaction (HER) was studied in 5 M KOH solution at room temeprature. The reason of revealed higher electrochemical activity towards the HER in case of the Ni+Mo nanocomposite electrode as compared to that of the Ni+W nanocomposite electrode, has been discussed.

Abstract: The Ni+Mo composite coatings were prepared by electrodeposition under the galvanostatic conditions (j_dep = -300 mA cm^-2) from the nickel plating bath containing a suspension of molybdenum powder with different granulation (<100 nm, 3-7 μm, <150 μm). Kinetics of hydrogen evolution reaction (HER) was studied in 5 M KOH solution at room temperature using steady-state polarization and electrochemical impedance spectroscopy (EIS) measurements. It was found that the rate of the HER is dependent on the granulation of Mo powder used as composite component. The highest kinetics of the HER was revealed for the Ni+Mo (3-7 μm) composite electrode, and the increase in its electrochemical activity was attributed to the increase in the real surface area development and the intrinsic activity.

Abstract: The Ni+W composite coatings were prepared by electrodeposition under the galvanostatic conditions (j_dep = -300 mA cm^-2) from the nickel plating bath containing an addition of tungsten powder of different granulation (<150 nm, 12 μm, <150 μm). For comparison, the Ni-W alloy coating was also obtained. Studies of hydrogen evolution reaction (HER) were carried out in 5 M KOH solution at room temperature using steady-state polarization and electrochemical impedance spectroscopy (EIS) measurements. It was found that for the Ni+W (<150 μm) composite coating increase in the activity of HER was observed in comparison with the others coatings.

Abstract: The Ni-P, Ni-Co-P and Ni-P+Co coatings were obtained in galvanostatic conditions at the current density of j_dep= -200 mA cm^-2. A stereoscopic microscope was used for surface morphology characterization of the coatings. The X-ray diffraction (XRD) method was used to determine phase composition of the coatings and the atomic absorption spectrometry (AAS) was applied to specify their chemical composition. The behavior of the obtained coatings was investigated in the process of hydrogen evolution reaction (HER) from 5 M KOH using steady-state polarization and electrochemical impedance spectroscopy (EIS) methods. It was found that introduction into Ni-P amorphous matrix powder of cobalt produced porous electrode materials which could be used for the HER.

Abstract: The Ni+W+Mo+Si composite coatings were prepared by electrodeposition under the galvanostatic conditions (j_dep = -100 mA cm^-2) from the nickel bath containing powders of tungsten, molybdenum and silicon. Thermal treatment of the obtained coatings was conducted in argon atmosphere. Chemical composition of the coatings was determined by energy dispersive spectrocopy (EDS). Phase composition investigations were conducted by X-ray diffraction (XRD) method. Studies of electrochemical corrosion resistance were carried out in 5 M KOH solution. On the basis of these investigations it was found that Ni+W+Mo+Si thermally treated coating is more corrosion resistant than Ni+W+Mo+Si as-deposited coating.

Abstract: The electrodeposited Ni-P coatings are commonly used for their electrocatalytic properties towards hydrogen evolution reaction. However, their corrosion resistance in concentrated alkaline solutions is still less known. In this work, the effect of phosphorus on the resistance of nickel electrodeposits to electrochemical corrosion in 5 M KOH solution, was studied. Open circuit potential and anodic polarization measurements were performed to determine parameters of the corrosion resistance of the crystalline Ni deposit and amorphous Ni-P electrocoating. It was found that alloying of nickel with phosphorus is the effective manner of the improvement of the corrosion resistance of the nickel coatings. The obtained Ni-P electrode material contained 10 wt.% of P and revealed amorphous structure. The increase in the corrosion resistance of the Ni₉₀P₁₀ system as compared to that determined for comparable Ni polycrystalline electrode was due to phosphate formation responsible for broad passivation potential in alkaline medium and amorphous structure.

Abstract: The coulometric or anodic de-plating technique can be used for measuring the thickness of coatings on virtually all substrates such as steel, non-ferrous metals or insulating material bases. This study reports on application of an electrochemical de-plating technique for measuring the thickness of multilayer Ni/Cu coatings electrodeposited on a steel substrate. Principles of a coulometric method by local anodic dissolution according to ISO 2177:2003 have been explained. The phase analysis of the Ni/Cu multi-layer coatings was performed using GIXD technique. The summary of the GIXD diffraction patterns obtained in this experiment indicates that such electrocoating is composed of two sub-layers of nickel and copper.

Abstract: The electrode processes are often studied on iron for the needs of hydrogen technologies. This paper presents the use of the resources of the “MicroScan” program in manual methods to determine the stereological parameters of the Armco iron. For this purpose, the average number of particles per one unit of the N_A surface area and the average surface area of the grains in the 〈A flat structure were determined, using the planimetric, the Jeffries and the comparative methods. The linear method was used to determine the average number of segments per one length unit of the N_L structure and the average length of the circuits of grains in the 〈L flat structure. It was found out that the mean values of the determined parameters were in line with the PN-84/H-04507 standard and small differences existing in the obtained results were due to the jumping character of the pattern scale of the mentioned standard. The relative error of the N_A and A parameters indicates that the planimetric method allows to achieve the most accurate measurement of the size of the grain.

Abstract: Knowledge of the mechanism and the kinetics of hydrogen evolution reaction (HER) is essential for tailoring new electrode materials with electrocatalytic activity towards HER. This review paper deals with some problems related to determination of the kinetics of multi-step reaction of HER, especially on porous electrodes. Theoretical background of HER has been briefly presented. The importance of electrochemical impedance spectroscopy (EIS) method for studies of the detailed mechanism and kinetics of HER and some problems in understanding of the interpretation ac impedance results, have been discussed.

Abstract: Effect of hydrogen on metals is a complex phenomenon. The objective of this paper was to outline the recent application of scanning Kelvin probe (SKP) for a deeper understanding of nature and properties of metal-hydride system. SKP belongs to the family of scanning probe electrochemistry techniques (SPETs) that are currently used and developed. Different applications of SKP technique for hydrogen detection in metals, hydrogen permeation through metals with high local resolution, and quantitative analysis of hydrogen in materials, were presented. The emphasis in this work was on presenting specific applications of SKP rather than extensive reviews; details of how and why this technique is useful in research area was given.