Influence of water content and applied potential on the electrodeposition of Ni coatings from deep eutectic solvents

Abstract

Ni coatings were electrodeposited from 1:2 choline chloride (ChCl)-urea (U) deep eutectic solvents (DESs) on low carbon steel. We report on the interrelated influence of water content in the electrolyte and applied potential on the formation of Ni films and their chemical composition and morphology. This was investigated by cyclic voltammetry (CV) and chronoamperometry (CA) in combination with ex-situ characterization techniques (FE-SEM, EDS, XPS and Raman spectroscopy). Ni electrodeposition from DES is shown to be highly complex: Ni þ2 reduction is followed by water reduction, which triggers electrolyte decomposition. A water content higher than 4.5%wt and/or performing electrodeposition at potentials more negative than E ¼ À0:90V vs Ag quasi-reference electrode enhances the decomposition of the solvent. This breakdown appears via either an electrochemical reaction or triggered by water splitting. In both cases, it leads to the incorporation of DESs decomposition products, such as trimethylamine and acetaldehyde within the Ni film. Under these conditions, the films are composed of metallic Ni and NiO x (OH) 2(1Àx) .

Water distribution at the electrified interface of deep eutectic solvents

“…This will allow us to control the thickness and the morphology of the deposited layers precisely. 57 At a highly negatively charged surface (Fig. 3(a and h), s ¼ À0.32 C m À2 ), the number density prole as well as the water distribution close to the interface follows a completely different trend.…”

“…Recently, this has been conrmed experimentally using combined electrochemical and surface analysis techniques. 56,57 On the other hand, in closed electrochemical systems, such as batteries and supercapacitors, high surface polarization leads to electrolysis of water in the vicinity of the electrode surface which results in formation of hydrogen and oxygen gas. Because of the gas formation, the internal pressure increases and the active site/pores of the electrode surface are blocked by the gas bubbles.…”

Potential Application of Ionic Liquids for Electrodeposition of the Material Targets for Production of Diagnostic Radioisotopes

“…They reported that a residual water content leads to Ni and Ni(OH) 2(ads) . Lukaczynska et al [ 78 ] reported significant influence of water content on electrodeposition of Ni from ChCl:urea solutions. Higher than 4.5%wt water content enhances decomposition of the solvents at potentials lower than −0.9 V vs. Ag as quasi-reference electrode (QRE).…”

The role of hydrogen bond donor and water content on the electrochemical reduction of Ni2+ from solvents – an experimental and modelling study

“…The strong influence of H 2 O on the viscosity and conductivity of the solvents has been reported in many occasions 15,[21][22][23] . More recently, it has also been shown that water affects the dynamics and the electrochemistry of active species 15,21,24,25 . In addition, computational modelling together with experimental techniques have shown that small amounts of H 2 O hydrate first the Cl − , and therefore strengthen the HBD-HBD and Ch + -HBD interactions 17,[26][27][28] .…”

“…This has been described to happen for concentrations of H 2 O higher than 50 wt% 17,26,29 . As a result, a constant monitoring of the water content becomes mandatory for a proper understanding and use of DESs in many chemical [30][31][32] and electrochemical processes 17,21,24,25,33,34 .…”