Effect of Thiourea Containing Composite Additives on Nickel Electrodeposition in Ammoniacal Solution

Composite additives have an important influence on the process of metal electrodeposition and the quality of a metal deposited layer. In this work, the additive thiourea (TU) was compounded with cetyltrimethyl ammonium chloride (CTAC), sodium dodecyl sulfate (SDS) and polyethylene glycol 20,000 (PEG20000), and their effect on the cyclic voltammetric behavior, electrochemical nucleation mechanism, crystallographic orientations and surface morphology of the nickel electrodeposition in ammoniacal solution were experimentally investigated. The results show that the introduction of composite additives resulted in a stronger cathodic polarization and increased the nucleation overpotential (NOP) values significantly, which had an important impact on forming compact and smooth nickel deposits. The chronoamperometry analysis indicated that the reduction in nickel followed the 3D progressive nucleation mechanism in the presence of composite additives at the step potential of -1.16 V and -1.18 V. Smoother and finer nickel films were found using scanning electron microscopy (SEM) images as the composite additives were used. X-ray diffraction revealed that all nickel deposit samples had the face-centered cubic structure, and five main crystal planes were displayed by the presence of composite additives in the electrolyte. Furthermore, the diffraction peaks of (111) and (200) crystal planes were slightly shifted toward lower 2 theta values when thiourea was used in combination with additive CTAC or PEG20000. These results were beneficial for understanding the mechanisms and facilitating the rational design of additives for metal nickel electrodeposition.

Automated summary

Composite additives play a crucial role in the metal electrodeposition process and the quality of the deposited metal layer. This study investigated the effects of composite additives consisting of thiourea (TU), cetyltrimethyl ammonium chloride (CTAC), sodium dodecyl sulfate (SDS), and polyethylene glycol 20,000 (PEG20000) on the cyclic voltammetric behavior, electrochemical nucleation mechanism, crystallographic orientations, and surface morphology of nickel electrodeposition. The results showed that the introduction of composite additives led to stronger cathodic polarization, increased nucleation overpotential, and the formation of compact and smooth nickel deposits. The use of composite additives also resulted in smoother and finer nickel films. X-ray diffraction analysis revealed the presence of specific crystal planes when composite additives were used. The findings provide insights into the mechanisms and design of additives for metal nickel electrodeposition.