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 2θ 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.