Solid State Phenomena Vol. 228

Abstract: Electrodeposited Ni-P, Ni-W-P, Ni-P+W and Ni-P+NiO+W coatings were obtained in the galvanostatic conditions at the current density j_dep = -200 mA cm^-2. A stereoscopic microscope was used for surface characterization of the coatings. The phase composition of the coatings was determined using X-ray diffraction (XRD) method. The chemical composition of the deposits was determined using atomic absorption spectroscopy (AAS). It was found out that the introduction of the tungsten powder in one case, and the nickel oxide and tungsten powder in the other into the electrolytic Ni-P matrix results in obtaining the coatings with a very rough surface. The coatings obtained in this way may be useful while applying them as electrode materials in electrochemistry.

Abstract: The Ni+Al+Ti composite coatings were prepared by the electrodeposition under the galvanostatic conditions at the deposition current denisty of j_dep = -225 mA cm^-2. Phase composition investigations were conducted by X-ray diffraction (XRD) method. The surface morphology, cross-section and chemical composition of the coatings were examined using a scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. Thermal treatment of the obtained composite coatings was conducted in argon atmosphere at the temperature of 800^oC for 12 h. It was found that the as-deposited Ni+28at.%Al+25at.%Ti composite coating is a three-phase material (Ni, Al and Ti phases). The thermal treatment caused the chemical reaction in solid state of the heated coating, and a new multi-phase material was formed containing Ni and Al metallic phases as well as NiAl, Ni₂Al₃, Ni₃Al, NiTi, NiTi₂ and Ni₃Ti intermetallic phases. Thus obtained composite coatings may be useful in the applications as materials in the electrochemical processes.

Abstract: The Ni+W+Si and Ni+W+Mo+Si composite coatings were obtained by electrodeposition of crystalline nickel from an electrolyte containing suspension of suitable metallic and non-metallic components (W, Mo and Si). These coatings were obtained under galvanostatic conditions, at the current density of j_dep = -0.100 A cm^-2 and at the temperature of 338 K. For comparison the Ni coating were also obtained and investigated in the same manner. Obtained coatings were modified in the air atmosphere by thermal treatment at the temperature of 973 K for 1 h. Thus obtained coatings may be useful in application as electrode material for the oxygen evolution reaction.

Abstract: Electrocatalysis as a catalytic process involving oxidation or reduction through the direct transfer of electrons is of key importance subject in various fields of chemistry and associated sciences. Heterogeneous electrocatalysis is especially important to the development of water oxidation and fuel cells catalysts. This paper presents the brief description of the electrocatalysis and the mechanism of electrochemical reactions. Different factors and their influence on electrocatalytic activity, have been discussed. Role of nanoparticles in electrocatalysis received a particular emphasis. Long-term tasks of electrocatalysis were also definied.

Abstract: One way to obtain hydrogen of high purity on an industrial scale is the electrolysis of water. New electrode materials with the catalytic ability to reduce the energetic barrier of the process have been looked for for many years. The possibility of tailoring the catalytic properties of the electrode material by obtaining it through electrolysis is of particular interest. These electrode materials include materials based on the amorphous nickel matrix containing TiO₂ as its crystalline phase and non-stoichiometric titanium oxides which, thanks to their coexistence in the layer, make up effective oxidation-reduction pairs that catalyse the evolution of hydrogen. The following study is a critical analysis of the parameters characterizing the Ni-P+Ti oxides composite layers for hydrogen evolution. It includes a discussion on the correlation between the chemical and phase composition, morphology, surface development and roughness of the composite layer and its activity in the process of hydrogen evolution. It was found out that the Ni-P+Ti oxides layers can be recommended as cathode electrode materials for the electrolysis of water.

Abstract: Oxygen electroevolution reaction (OER) was studied in alkaline medium on the Ni-P+TiO₂ composite electrocoatings obtained from the Watts type bath containing the suspension of TiO₂ particles. The comparable Ni-P coatings were electrodeposited from the supporting electrolyte without titanium dioxide. The galvanostatic electrodeposition of all coatings was conducted on a polycrystalline copper substrate at the deposition current density of 240 mA cm^-2 for 30 min. The electrolysis process was carried out at temperatures of 293-333 K. It was found that the mass increment and the content of TiO₂ in the obtained coatings is a decreasing function of the electrodeposition temperature. It was also acertained that the built-in TiO₂ as the composite component into the Ni-P matrix has no effect on the improvement of the electrocatalytic properties of the Ni-P+TiO₂ composite electrodes towards OER probably due to limitation of the size of the electrochemically active surface area of the electrode material obtained under proposed conditions.

Abstract: Electrochemical characteristics of the composite Ni-P+TiO₂ electrocoatings with a differentiated content of TiO₂ composite component from 14 to 20 at.%, dependent on temperature conditions of electrodeposition from 293 to 333 K, was carried out in an alkaline 2.5 M NaOH solution. Cyclic voltammetry studies of the Ni-P+TiO₂ coatings and comparable Ni-P electrocatalysts revealed that cyclic cathode-anode polarization activated TiO₂ as the embedded composite component for the Ni-P+TiO₂ coating obtained at 333 K only.

Abstract: The object of this work were composite electrocoatings with an amorphous Ni-P matrix containing crystalline NiO or Ni (OH)₂ component. The Ni-P+NiO, Ni-P+Ni (OH)₂ and Ni-P electrocoatings were deposited on a Cu substrate under galvanostatic conditions at room temperature. The electrocatalysts were characterized in the process of hydrogen evolution in 5 M NaOH solution in dependence on their deposition conditions, phase composition and chemical constitution. Based on the potentiodynamic polarization curves, the parameters of the Tafel equation and exchange current densities, were determined as a criterion for estimation of catalytic properties of these electrode materials towards hydrogen evolution reaction in an alkaline medium.

Abstract: The Ni+Cr+Si, Ni+Mo+Si and Ni+W+Si composite coatings were obtained by electrodeposition of crystalline nickel from an electrolyte containing suspension of suitable metallic and non-metallic components (Cr, Mo, W and Si). These coatings were obtained galvanostatically at the current density of j_dep = -0.100 A cm^-2 and at the temperature of 338 K. Chemical composition of the coatings was determined by energy dispersive spectroscopy (EDS). The electrochemical activity of these electrocatalysts was studied in the process of hydrogen evolution reaction (HER) in 5 M KOH solution using steady-state polarization and electrochemical impedance spectroscopy (EIS) methods. The kinetic parameters of the HER on particular electrode materials were determined. It was found that Ni+Mo+Si composite coatings are characterized by enhanced electrochemical activity towards the HER as compared with Ni+W+Si and Ni+Cr+Si coatings due to the presence of Mo and increase in electrochemically active surface area.

Abstract: The Ni+MoS₂ composite coatings were obtained by electrolytic co-deposition of crystalline nickel with molybdenum sulfide powder from an electrolyte containing suspension of this powder. For comparison, the Ni coating was also deposited. These coatings were obtained in galvanostatic conditions at the current density of j_dep = -250 mA cm^-2. A scanning electron microscope was used for surface morphology characterization of the coatings. The behavior of the coatings was investigated in the process of hydrogen evolution reaction from 5 M KOH solution using steady-state polarization and electrochemical impedance spectroscopy methods. It was found that introduction of molybdenum sulfide into nickel matrix, evokes developed and rough surface which is the reason for the increase in the rate of the HER as comapred to the smooth Ni electrode. Thus obtained coatings may be useful in application as electrode materials for the HER.