Zinc electrodeposition in the presence of polyethylene glycol 20000

The influence of polyethylene glycol 20000 (PEG₂₀₀₀₀) on the mechanism of zinc deposition and nucleation was studied by voltammetry, chronoamperometry, and atomic force microscopy (AFM). The electrodeposition of zinc in an electrolytic bath containing PEG₂₀₀₀₀ occurs via two reduction processes with different energies that involve the same species, ZnCl₄²⁻: the first reduction process occurs at E_PI′c = −1.25 V, SCE, whereas the second process, which corresponds to the bulk deposition of Zn, occurs at E_PII′c = −1.6 V, SCE without significant interference from the hydrogen evolution reaction. Analysis of chronoamperograms obtained in the absence and presence of PEG₂₀₀₀₀ indicates that distinct nucleation mechanisms are involved during the initial stages of Zn deposition. In the absence of PEG₂₀₀₀₀, the transients are consistent with the model of 3D diffusion-controlled nucleation. In the presence of PEG₂₀₀₀₀, however, the transients exhibit a more complex form involving two simultaneous nucleation and growth processes: 2D instantaneous nucleation limited by the incorporation of adatoms (2D_i-li) and a diffusion-controlled 3D nucleation mechanism (3D_-dc). Characterization of the surface morphologies of the zinc deposits by AFM imaging confirmed our conclusions drawn from the electrochemical studies. SEM analysis showed that the zinc coatings obtained in the presence of PEG₂₀₀₀₀ at −1.6 V, SCE are smoother and more compact.