Research Into Effect of Propionic and Acrylic Acids on the Electrodeposition of Nickel

Abstract

Nickel coatings are widely used in machine-building, electronics, automotive and aerospace industries. High requirements for environmental safety and operational performance of contemporary processes of electrochemical nickel plating predetermine the search for the new electrolytes. Electrolytes based on carboxylic acids are characterized by high buffer properties, ecological safety, and enhanced values of limiting current. Heuristic approach when fabricating comprehensive electrolytes, based on empirical data, does not make it possible to conduct predictable optimization of the formulations of nickel plating electrolytes. Solving this problem seems possible when using a quantum-chemical simulation. In this work, we performed quantum-chemical calculations for the propionate and acrylate complexes of nickel. It was established that coordination numbers of the propionate and acrylate complexes of nickel are equal to five and six, respectively. It is shown that electroreduction of the propionate nickel complex proceeds with the formation of an intermediate particle. The negative charge of this particle is localized on the intrasphere molecules of water. This may lead to the electroreduction of the latter and to an increase in the pH of a near-electrode layer. In the intermediate particle of the acrylate complex, localization of the charge occurs on the vinyl fragment of acrylate-ion. Electrochemical reaction of reduction of the coordinated water molecules in such a particle is not energetically favorable. It was established that the isolation of nickel from the acrylate complex proceeds with lower kinetic difficulties than from the propionate complex. An assumption was made that fewer insoluble hydroxide nickel compounds, which block the cathode surface, form in the acrylate electrolyte.Such an assumption is based on the fact that given close buffer properties of acids, electroreduction of the acrylate complexes does not imply the involvement of coordinated water molecules in the electrode process. The results obtained are very valuable for selecting the nature of carboxylic acid as a component for the complex nickel plating electrolyt