Effect of Chloride Ion on Electrochemical Behavior of Silver Electrodeposition in ChCl-Urea Low Eutectic Solvent

Abstract

Metallic silver coating has been widely used in the fields of microelectronics industry, catalyst, sensor and preparation of magnetoresistive materials because of its excellent corrosion resistance, good lubricity, high conductivity, excellent decoration and high catalysis. Compared with the traditional aqueous solution system, the research on metal electrodeposition in ionic liquid system is developing rapidly. In addition, additives are the key factors in the silver plating process. Adding a small amount of organic or inorganic additives to the plating solution will significantly change the coating properties, such as improving brightness, hardness and ductility. In this paper, using choline chloride urea (ChCl-Urea) low eutectic solvents (DESs) as the base solution, cyclic voltammetry (CV), chronoamperometry (CA), Tafel polarization and other electrochemical methods were used. The effect of chloride ion on the electrochemical behavior of silver electrodeposition was deeply studied. The phase composition and micro morphology of the silver coating were also studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The existing forms and main discharge complexes in the presence of NH₄Cl in the plating solution were studied by the classical gerisher exchange current density method. The results showed that the addition of chloride ion in ChCl-Urea system changed the reduction potential of Ag⁺ (vs. Ag|AgCl), and Ag⁺ in the plating solution formed complex [AgCl_n]^1-n, which makes the reduction potential shift negatively from -0.85 V to -0.98 V. The increase of overpotential was conducive to the formation of silver coating with good performance. By comparing the fitting CA curve with the theoretical curve, it is found that the nucleation mode of Ag(I) in ChCl-Urea DES was related to the concentration of chloride ion. The nucleation mode at low concentration had the mixed nucleation characteristics of three-dimensional instantaneous nucleation and three-dimensional continuous nucleation, and the nucleation mode at high concentration conformed to three-dimensional instantaneous nucleation. The results of gerisher exchange current density analysis revealed that the main discharge complex ion in the plating solution was [AgCl₂]^-. The addition of chloride ion inhibited the formation of dendritic silver coating. At the same time, this paper provides a method for preparing compact spherical pure silver coating. As means of preparing nanospherical silver, electroplating is the main direction of future research. Basic research on relevant additives is also essential. In the process of silver plating, the action mechanism of additives needs to be further studied. This plays an important guiding role in the development of electroplating additives and electroplating process.

Keywords

choline chloride-urea deep eutectic solvent / silver electrodeposition / additive / complex compound / electrochemical behavior

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