Nucleation and growth mechanism of Cu-Zn/AgNPs composite coatings at different concentrations of silver nanoparticles (AgNPs) in solution

Abstract

Atomic force microscopy (AFM), X-ray Diffraction (XRD), and electrochemical techniques (voltammetry and chronoamperometry) were used to evaluate the influence of the concentration of silver nanoparticles (AgNPs) on the electrodeposition and nucleation mode of Cu-Zn/AgNPs composite coatings. The voltammetry analysis display three reduction processes during the formation of the Cu-Zn/AgNPs metal composite. The first process (peakPCI) appears in the potential range of -0.5 to -1.2 V vs. saturated calomel electrode (SCE) and corresponds to the reduction of Cu(II) to Cu(0). The second and the third processes, peak PCII and PCIII, respectively are located in the range of -1.4 to -1.6 V vs. SCE and are associated with the deposition of various crystalline phases of the Cu-Zn alloy. The potential of the PCI peak is shifted in the negative direction by increasing the concentration of AgNPs in the electrolytic solution. This effect is related to the adsorption of AgNPs on the substrate surface. From the chronoamperometry study, it was possible to disclose a process of nucleation and growth of phases in the potential region where the peak PCI is formed. This nucleation process may be explained in terms of a combination of an adsorption process and a diffusion-controlled three-dimensional crystal nucleation and growth mechanism (3D−dc(PcI)). In the potential range where the PCII and PCIII peaks appear, a second nucleation process take place. This nucleation process involves three mechanisms: an adsorption process and two three-dimensional (3D) mechanisms of the kinetics of nucleation and diffusion-controlled growth of bimetallic phases (3Ddc−bimetal) that correspond to the nucleation of various phases of the alloys. On the other hand, a decrease in the nucleation kinetics parameters (density of active sites formed (N0) and the nucleation rate (A)) is observed with the increasing concentration of the AgNPs in the electrolytic solution. XRD analysis confirmed the formation of various crystalline structures of the Cu-Zn alloy at -1.50 V vs. SCE. Furthermore, AFM showed that the morphology and size of the formed metal clusters strongly depend on the content of the AgNPs in the bath.