The effect of different factors on electrochemical obtaining of alloys Re-Te-Cu

Based on the study of volt-ampere dependencies during electroreduction of rhenium (VII), tellurium (IV) and copper (II) ions from hydrochloric acid electrolyte on Pt electrode, the conditions of deposition of nano-coatings of ternary Re-Te-Cu alloy were determined. The influence of various factors such as amounts of individual components and total con­cen­tra­tions of components in the electrolyte solution, temperature, concentration of hydro­chloric acid, etc., on the composition and quality of coatings was studied. It was establ­i­shed that with the increase of rhenium concentration in the electrolyte, as well as increase of temperature, the rhenium content in deposits increased. The morphology of films depo­sited on platinum substrate was studied using the scanning electron microscopy. Based on the experimental data, the following electrolyte composition (mol/l) is recommended for obtaining the semiconductor Re-Te-Cu alloy containing 40-50 wt.% Re: (6.9·10-4-6.9·10-3) KReO4 + (9·10-4-1.8·10-2) TeO2 + (6·10-4-1.2·10-2) CuCl2·2H2O +2 HCl, T = 75 °C.

ELECTROCATALYSIS OF THE HYDROGEN EVOLUTION REACTION ON CoRe, CoWRe SUPERALLOYS DEPOSITED FROM CITRATE ELECTROLYTE

The reaction of electroreduction of hydrogen ions on binary CoRe and ternary CoWRe alloys electrodeposited from a citrate electrolyte with different amount of potassium perrhenate (0.01 and 0.05 mol·L-1) depending on the deposition current density (5–40 A·cm-2) has been investigated by the method of stationary voltammetry. The kinetic parameters of the reaction have been calculated, and it is shown that the use of ternary alloys allows one to increase the value of exchange current density by almost an order of magnitude and significantly reduce the overvoltage of hydrogen reduction in comparison with cobalt. It is shown that the best electrocatalysts for the reduction of hydrogen in alkaline solution can be ternary CoWRe alloys with a rhenium content of 15–20 at. %.

PECULIARITIES OF ELECTRODEPOSITION OF COBALT—WOLFRAM—RENIUM ALLOY

The methods of stationary voltammetry and chronovoltammetry have been used to study deposition processes of ternary CoWRe alloys at different rhenium content of the electrolyte and deposition current density. It has been found that the limiting currents have a diffusive nature and are proportional to the concentration of perrhenate ions in the electrolyte. The CoWRe alloys should be formed by the discharge of bimetallic citrate complexes of the following composition [(Co)(WO4)(H)(Cit)]2- and rhenium electrodeposition. Rhenium does not form complexes with citrate ions and deposits better in an alloy with iron group metals than in the form of an individual metal from a perrhenate solution. It can be assumed that the discharge of rhenium into the alloy occurs from a surface complex, the nature of which has not yet been established. The alloy current efficiency reaches 93% due to the high overpotential of hydrogen evolution on the alloy surface. According to the results of investigations of the catalytic properties of alloys in the hydrogen reduction reaction, it has been found that with increasing the rhenium content of the electrolyte and alloy, an increase in hydrogen overpotential is observed. Based on the Tafel coefficients found, it was found that in an acidic and neutral medium, the limiting stage of the cathodic and anodic reaction is the transfer of the first electron. In an alkaline medium, the anode process is complicated by the simultaneous transport of two electrons. The found values of corrosion resistance are 1-2 kOm·cm-2 in solutions of 0.01 M H2SO4; 20-110 kOm·cm-2 in 2.5% NaCl; 10-30 kOm·cm-2 in 1.0 M KOH. Based on the dependence of corrosion resistance on the refractory metals content of the alloy and the electrodeposition conditions, the optimum deposition current density of 10 mA·cm-2 has been found.