Bright metal coatings from sustainable electrolytes: the effect of molecular additives on electrodeposition of nickel from a deep eutectic solvent

Abstract

Organic and inorganic additives are often added to nickel electroplating solutions to improve surface finish, reduce roughness and promote uniform surface morphology of the coatings. Such additives are usually small molecules and often referred to as brighteners or levellers. However, there have been limited investigations into the effect of such additives on electrodeposition from ionic liquids (ILs) and deep eutectic solvents (DESs). Here we study the effect of four additives on electrolytic nickel plating from an ethyleneglycol based DES; these are nicotinic acid (NA), methylnicotinate (MN), 5,5-dimethylhydantoin (DMH) and boric acid (BA). The additives show limited influence on the bulk Ni(II) speciation but have significant influence on the electrochemical behaviour of Ni deposition. Small concentrations (ca. 15 mM) of NA and MN show inhibition of Ni(II) reduction whereas high concentrations of DMH and BA are required for a modest difference in behaviour from the additive free system. NA and MN also show that they significantly alter the nucleation and growth mechanism when compared to the additive free system and those with DMH and BA. Each of the additive systems had the effect of producing brighter and flatter bulk electrodeposits with increased coating hardness but XRD shows that NA and MN direct crystal growth to the [111] orientation whereas DMH and BA direct crystal growth to the [220] orientation.

Effect of Sodium Bromide on the Electrodeposition of Sn, Cu, Ag and Ni from a Deep Eutectic Solvent-Based Ionic Liquid

“…Ni species in 1:2 ChCl:EG-based liquid started to reduce at -0.7 V, comparable with our previous work which described the electrodeposition of Zn-Ni alloy from Ethaline 200-based ionic liquids. [19] Recently, the Ryder group investigated the electrochemical properties of Ni species in eutectic liquids [63,64] in which it was found that Ni species started to reduce at about -0.65 V, which is extremely close to the redox potential of the Ni complexes studied in this work. Fig.…”

“…Recently, Ryder and co-workers investigated the effects of nicotinic acid, boric acid and methylnicotinate on the electrodeposition of Ni from eutectic solvents, where they found that these additives can increase the growth rate of the deposition. [64,72] Thus, a more in-depth study needs to be performed to investigate the mechanism of electrodeposition of Ni and other metals from eutectic solvents. This might be achieved by examining the nucleation and the mechanism of metal growth through the use of chronoamperometry and atomic force microscopy (AFM).…”

On the Control and Effect of Water Content during the Electrodeposition of Ni Nanostructures from Deep Eutectic Solvents

“…Moreover, the wave (R 3 ) was attributed to a cathodic breakdown of the DES that is catalysed by the Ni NPs deposited beforehand on the surface of the electrode. [16][17][18][19]39 N i the amount of water (up to 7.51 wt%) enhances the currents of the waves R" 1 (onset at E = −0.18 V for the blue curve) and R" 2 (onset at E = −0.67 V for the blue curve) and decreases drastically the potential window (purple and blue curves). First tentative assignment of these two processes could be to the adsorption of water on the polycrystalline nickel electrode 3,55 (eq.…”

“…14,15 For these reasons, the number of publications on electrodeposition from DES is spectacularly increasing, notably for nickel. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] The electrodeposition from these non-aqueous baths have proven successful to obtain nickel coatings, [18][19][20]34 nickel-based alloys 21,22,24,25,27,28,35 and nanostructured nickel films for corrosion resistance. 29,30 Similarly, DES were also used for the synthesis of a multitude of nanostructures (Pd, 36 Au, 37 ...), due to the capability of these solvents to slow down the electrochemical processes, thus, having a better control of the deposition of nanostructures.…”

Ni/cerium Molybdenum Oxide Hydrate Microflakes Composite Coatings Electrodeposited from Choline Chloride: Ethylene Glycol Deep Eutectic Solvent

“…Moreover, from baths based on eutectic solvents it is possible to obtain Ni coatings on an aluminum substrate. Obtaining bright Ni coatings requires the use of brighteners, which differ from those used in aqueous plating baths [9,10]. The important influence on the coating's deposition from DESs is the water content in a plating bath.…”