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

Andrew P Abbott,Andrew Ballantyne,Robert C Harris,Karl S Ryder,Jamil A Juma

doi:10.1039/c6cp08720e

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.

Highlights

It is estimated that 105 metric tons of nickel and nickel salts were consumed worldwide in 2011 through nickel electrodeposition processes.1 Electrolytic nickel coatings are commonly applied as decorative and/or functional coatings as well as use in electroforming processes
Despite the increasing complexity in the chemical variety of deep eutectic solvents (DESs) electrolytes, the ion speciation of dissolved metal salts is mostly dominated by the formation of low coordination number chloro complexes such as AuCl which forms the linear [AuCl2]- complex33 or CuCl2 which forms the tetrahedral [CuCl4]2- complex29 when dissolved in the DES Ethaline at room temperature
In this study we have shown that bright, hard adherent nickel coatings can be obtained at high current efficiency from a simple Deep Eutectic Solvent in the presence of low concentration of additive

Summary

Introduction

It is estimated that 105 metric tons of nickel and nickel salts were consumed worldwide in 2011 through nickel electrodeposition processes.1 Electrolytic nickel coatings are commonly applied as decorative and/or functional coatings as well as use in electroforming processes.

Results

Conclusion