PROPOSED COMPOSITION OF COMPLEXES AND ION ASSOCIATES IN CITRIC ACID SOLUTIONS CONTAINING NICKEL SULFAMATE AND POTASSIUM PERRHENATE

The article presents an analysis of the experimental data available in the scientific literature on the conditions for obtaining nickel-rhenium alloys, promising as cathodes for electrolytic hydrogen production. The problem of searching for additional evidence of the mutual influence and interaction of nickel (II), citrate and perrhenate ions in the deposition electrolyte is formulated. For this purpose pH-metric titration of solutions containing (1) citrate ions only; (2) citrate and nickel(II) ions; (3) citrate, nickel(II) and potassium perrhenate ions – was carried out in the pH range from 1.5 to 2.0. Simultaneous release of protons associated with both the reaction of nickel with citrate to form the corresponding NiHCit- complexes and the reaction of citrate with perrhenate to form the (ReO4∙H2Cit)2- complexes was shown. Since the total concentration of reacted protons in the solution with nickel (II) and perrhenate corresponds to the sum of the concentrations of nickel and perrhenate ions, this confirms that reaction of complexes of citrate/perrenate formation occurs simultaneously (in parallel) with the reaction of the formation of the nickel-citrate complexes. And further pH arising should lead to well-known formation of NiCit24- complexes, which can be associated with two ions of perrenate. Based on the analysis of date concerning the influence of the components of nickel-­rhenium alloy deposition electrolytes on electrodeposition results, it was concluded that the predominant form providing the observed results concern both high current yield and high rhenium content in the alloy is an electrochemically inactive ion associate consisting of the NiCit24- complex and two perrhenate ions. Destroying in the near-cathode solution layer, it provides a periodic predominance of perrhenate ions, which can be restored without kinetic difficulties. The composition of complexes and ionic associates is proposed for a wide range of experimental data on the induced deposition of nickel-rhenium alloy coatings from citrate electrolytes, based on the quantitative ratios of the complex components in the electrolyte and the pH value.