Solid State Phenomena Vol. 228

Abstract: This review work was focused on conventional and modern electrodes which play an important role in electrochemical systems. Among many types of existing electrode materials, some of the most prominent materials from the conventional (metals and their alloys, graphite and mixed metal oxides) and the modern (amorphous, modified and composite) electrodes, have been outlined. What is also discussed is the recent intensive usability of nanocrystalline electrodes of better properties than their microcrystalline equivalents, and development trend of electrode materials.

Abstract: This work deals with selected aspects of the formation of intermetallic phases and the occurrence of a synergistic effect in the electrochemical process taking place at such electrode materials. A comparison of the catalytic activity of a variety of metals and intermetallic compounds in the reaction of hydrogen electroevolution and absorption was carried out. It has been found that the catalytic activity of such combinations is much higher than the activity of their individual components and quite often also of precious metals. This paper is also aimed at understanding the electrocatalytic properties of electrodes based on the concept of “activity descriptors”. What is also discussed is the ability of different metals and intermetallic compounds to store hydrogen.

Abstract: Recently, many efforts have been made to develop new anode materials able to catalyze the oxygen electroevolution reaction (OER). This review summarizes recent work undertaken on production and electroactivity of practical anode materials for an alkaline water electrolysis. Examples of mixed oxides with ABO₃ perovskite-type structure, metal compounds crystallizing in the spinel structure, electrolytic coatings of nickel alloys, as well as amorphous nickel-and cobalt-based electrolytic composite coatings, have been presented. The effect of the phase composition of the anode material on its activity in the OER, has also been discussed.

Abstract: Versatile applications and broad interest in amorphous electrode materials, especially the nickel-phosphorus coatings, primarily results from their unique properties and low-production costs in comparison to precious metals. This paper discusses the most important research conducted over several years into the Me-P layers, in particular the Ni-P and Ni-Me-P ones, which led to only partial understanding of these amorphous alloys. Methods of increasing the catalytic activity of the Ni-P layers in the process of electroevolution of hydrogen are also discussed because the electrolytic layers of amorphous nickel still seem to be the promising electrode material.

Abstract: The Ni-Me-P alloy coatings containing metal as alloying component (Me = Co, W) in a Ni-P amorphous matrix, were potentiostatically electrodeposited onto a polycrystalline Cu substrate. Deposition potential was established based on polarization curves of electrodeposition of Ni-Co-P, Ni-W-P and Ni-P alloy coatings. SEM, EDS, XRD and X-ray microanalysis methods, were applied for chemical and physical characterization of the obtained coatings. Linear analysis of Ni, Co and W distribution in the microregions of the appropriate alloy coating revealed that surface distribution of these elements is homogeneous what is due to a molecular mixing of the amorphous nickel matrix with the alloying components. It was found that the Ni-Co-P and Ni-W-P coatings have the amorphous structure like the Ni-P deposit and alloying components as Co or W are built-in into the appropriate coating in the amorphous form. The mechanism of the induced codeposition of these ternary Ni-Me-P coatings, has been discussed.

Abstract: The work concerns the literature review which unambiguously shows that the composite coatings which apart from the d-electron metal powder contain another component of the composite, i.e. the p-electron metal powder, have not been obtained so far. This kind of qualitative composition of the coating enables selective extraction of the p-electron metal from the nickel matrix of the composite, as well as – after heat treatment – results in the formation of the mixture of intermetallic phases with the hitherto unknown activity in the electrochemical processes.

Abstract: This work deals with the development of new electrochemical ways to improve the cathode activity towards hydrogen evolution reaction. An in situ composite electrodeposition technique has been proposed to obtain the porous Ni+MoO₂ coatings by simultaneous co-deposition of Ni and MoO₂ onto a Cu substrate from a nickel plating bath containing 10 g dm^-3 of MoO₂ powder suspended by magnetic stirring. Electrodeposition was conducted at 30°C at the deposition current density of j_d = 50-250 mA cm^-2. SEM, EDS, and XRD measurements, were applied for physical and chemical characterization of the obtained coatings. It was found that by controlling the deposition conditions it was possible to obtain porous Ni+MoO₂ coatings containing from 10 to 15 at.% of MoO₂. The XRD results confirmed their diphase structure with a polycrystalline Ni matrix into which a crystalline component in the form of MoO₂ particles was built-in.

Abstract: The mechanism of co-deposition of solid particles with metal ions has not been thoroughly explained so far. This, among others, results from a number of factors that influence the process and their mutual relations. Therefore, the present paper aims at deeper understanding of the mechanism of electrolytic co-deposition and the mathematical models developed over the years to describe the incorporation of solid particles into electrodeposited metals. In this review, three mechanisms explaining the process of co-deposition of solid particles with the metal matrix have been discussed: (i) the electrophoretic, (ii) the mechanistic, and (iii) the adsorption ones.

Abstract: Electrodeposition of polycrystalline nickel onto carbon steel substrate has been studied from different types of solutions: (bath I) the Watts nickel plating bath, (bath II) the sulfate-chloride nickel plating bath for production of the SUPER Ni coatings, (bath III) the sulfamate nickel plating bath, and (bath IV) the chloride nickel plating bath. A detailed study has been made on the influence of the bath composition on the mass increment and thickness of the deposited Ni coatings. Cathodic current efficiency of the Ni electrodeposition has been also studied. The electrochemical anodic de-plating technique has been used for measuring the thickness of nickel coatings according to ISO 2177:2003. Evaluation of the effect of bath composition on the quality of the galvanic nickel coatings, was carried out using the Hull cell. In a single test, the range of current densities which provided a desired plating characteristic at a given total current, was previewed. Principles of the electroplating process using the Hull cell have also been explained.