The effect of organic additives in electrodeposition of Co from deep eutectic solvents

Abstract

A range of organic/ inorganic additives have traditionally been added to electroplating solutions to improve brightness and encourage levelling. A limited number of studies have shown that some brighteners function in ionic liquids. In this study the effect of four additives; nicotinic acid (NA), methyl nicotinate (MN), 5,5-dimethyl hydantoin (DMH) and boric acid (BH), have been measured on the electrodeposition of cobalt in the 1choline chloride (ChCl): 2 ethylene glycol (EG) based deep eutectic solvent (DES). In general the addition of these additives causes the deposition potential of Co to be shifted to more negative over-potentials. No apparent change in speciation and coordination environment around the CoII centre was observed. The surface morphology was significantly changed by the addition of each of the additives, suggesting that they function by modifying the double layer. The nucleation and growth mechanism of Co deposition was found to change in the presence of these additives. Flat, shiny and high uniform cobalt layers were obtained with the additives whereas in their absence the deposit was black and dull. The additives significantly increased the hardness of the cobalt deposit and this was shown to be related to the crystal structure of the deposit which was determined using XRD.