Savchuk O. Electrosynthesis of nickel-based nanocomposites from methanesulfonate electrolytes

The thesis defines the basic characteristics of electrodepositing of nickel-based nanocomposites from methanesulfonate electrolyte and investigates the structure, physical-chemical and catalytic properties of the coatings. It has been shown that the titanium dioxide content of composites increases with increasing the concentration of TiO2 in the suspension and with decreasing the current density. The introduction of the dispersed phase into a nickel matrix leads to an increase in internal stresses, the microhardness of deposits and photocatalytic activity. A new technique is proposed to increase the photocatalytic activity of Ni-TiO2 composite by depositing it on a preformed nickel matrix with an extended surface. A technique for electrodepositing composites with a dispersed phase formed in the near-electrode layer in the form of insoluble hydrolyzed compounds of water-soluble precursors was applied. It has been established that the TiO2 content of Ni/TiO2 nanocomposites obtained from the true solution depends on the current density and Ni (II) concentration in the electrolyte. A comparison of the photocatalytic activity of catalysts obtained from a suspension electrolyte (Ni-TiO2) and those obtained from an electrolyte containing a soluble precursor (Ni/TiO2) shows that the latter exhibit higher photocatalytic activity for the same TiO2 content of the deposits. It has been shown that Ni/TiO2 catalysts obtained on an extended surface nickel matrix exhibit considerably higher photocatalytic activity than the similar deposits obtained on a smooth surface. It has been found that the amount of cerium-containing dispersed phase in Ni/CeO2 coatings increases with increasing the concentration of Ce (III) in the electrolyte, pH and current density. These composites exhibit a higher level of gloss, increased internal stresses, microhardness and electro-catalytic activity compared to the «pure» nickel coating. The basic characteristics of the nickel and phosphorus co-deposition from methanesulfonate electrolyte have been revealed. It is assumed that phosphorus is formed due to electrochemical reduction of hypophosphite anions and disproportionation reaction. It has been found that an increase in the concentration of hypophosphite anions in the electrolyte and higher pH values lead to an increase in the phosphorus content of the coatings. An increased current density results in a reverse effect. It has been found that an increase in the content of phosphorus in the deposits, which is observed with increasing the electrolyte acidity and sodium hypophosphite concentration, increases the gloss, microhardness, internal stresses and electrocatalytic activity of the coatings. It has been revealed that with increasing the phosphorus content of coatings, the magnetic saturation decreases, and the deposits become paramagnetic.