Bobrova L. Electrodeposition of chromium from ionic liquids containing chromium(III) chloride and choline chloride.

The thesis is devoted to the investigation of the basic features of electrodeposition of chromium coatings using deep eutectic solvents containing Cr(III) compounds. It was established that increasing the amount of water in low-temperature ionic liquids containing CrCl3, ChCl and H2O in the molar ratios of 1:0.5:x and 1:2.5:x respectively (where x = 6, 9, 12, 15 or 18) resulted in a decrease in density, surface tension and viscosity and an increase in conductivity. It was stated that the stepwise electroreduction of Cr(III) ions (with the formation of intermediates – compounds of Cr(II)) was accompanied by the hydrogen evolution reaction and the introduction of carbon into the electrodeposits via the chemical degradation of organic components of the electrolyte adsorbed on the electrode surface. It was determined that the water addition resulted in a sharp drop of the current efficiency of chromium electrodeposition and the deterioration of the surface appearance of coatings. An increased resistance to the anodic dissolution and corrosion of chromium-carbon coatings deposited from an electrolyte based on DES was established. It was shown that the protective ability of the coatings did not monotonically depend on the thickness of the coating. It was stated that the chromium-carbon coatings obtained from the electrolytes based on DES exhibited enhanced electrocatalytic properties towards the hydrogen evolution reaction in alkaline and acidic aqueous media. Key words: electrodeposition, chromium, chromium-carbon coatings, choline chloride, chromium(III) chloride, ionic liquids, deep eutectic solvents, functional properties.