R. Rashkov

Preparation of a Carbon Fiber-Nickel-Type Material and Investigation of the Electrocatalytic Activity for the Hydrogen Evolution Reaction

The preparation and the electrocatalytic activity of a new material of the type carbon fiber-nickel was investigated. Nickel growth on the carbon support was can-ied out through electrolysis. The kinetic of nickel deposition as a function of the electrolysis conditions was examined by cyclic voltammetry. The morphology and substitution of the nickel deposits, which at the beginning of the nickel growth proved to be of a globular type, were studied by scanning electron microscopy. It was established that a high degree of the carbon surface functionalization, achieved by double pulse oxidation, favored the nickel deposits on the oxidized carbon support. The electrocatalytic efficiency of nickel-modified carbon fiber electrodes was investigated by means of impedance spectroscopy for the hydrogen evolution reaction. The charge transfer resistance values of this reaction were significantly lower in the case of modified by nickel oxidized carbon fibers in comparison with the corresponding values for modified by nickel pristine fibers. The above values are in the order of magnitude of modified by noble metals, such as Pd and Rd, carbon fibers obtained through ion-exchange with the functional groups of the oxidized carbon fibers, and subsequent electrochemical or chemical reduction.

Polyhedral instability and transition to skeletal growth during electrocrystallization of cadmium

The formation of shallow cavities and the growth of skeletal forms of cadmium single crystals during electrocrystallization at high current densities was investigated. The similarity with the polyhedral instability during vapour growth of the same crystals was discussed. The maximum rate of stable growth and the critical slope of the step train in the centre of the crystal face were considered theoretically, which, when surmounted, lead to the transition from isometric to skeletal and dendritic growth. The transition forms have been deduced from the growth of macroscopically flat peripheries around the shallow cavities on the crystal faces.

Electrodeposition of Ni–Cu alloys at high current densities: details of the elements distribution

We report results from an experimental and modeling study of the far-from-equilibrium electrodeposition of Ni–Cu alloys by changing systematically the current density with focus on the surface structuring and surface content of the elements. General finding is that Cu prevails in the convex regions of the deposit, while Ni prevails in the concave ones. No deposition of a monophase is observed by the XRD analyses—in all samples are registered two phases under the form of solid solutions of Cu and Ni. With the increasing current density, the percentage of the major component increases towards deposition of pure Cu and Ni. Some oscillations of the overpotential with the current density are correlated with the Cu content in the Cu-rich solid solution. An original model based on Cellular Automata (CA) rationalizes the hypothesis that during their simultaneous deposition, Cu preserves the diffusion-limited growth mode, while the Ni discharges in a kinetically controlled one. The model is expected to be valid for lower current densities.

The role played by hydrodynamics in the levelling process during bright copper platting from acidic electrolytes. Part I

Abstract A new direct method has been developed for investigating the kinetics of levelling in a specially designed glass cell. The method was used to study the levelling mechanism during bright copper plating in acidic electrolytes. The role played by one of the important practical factors (the hydrodynamic conditions) is evaluated. It is shown that the velocity of circulation and the flow pattern of the electrolyte with respect to the cathode surface exert a substantial influence in establishing an optimum regime leading to the deposition of levelled coatings. By a suitable combination of the new method and a microspectrophotometric technique, the distribution of the levelling additive in the electrolyte layer adjacent to the microprofiled cathode was determined as a function of the hydrodynamic conditions. The results of this new approach confirm the adsorption-diffusion mechanism of electrochemical levelling.