The influence of pH and current density for nano-silver electrodeposited in cyanide-free succinimide bath

Abstract

The effects of pH and current density on cyanide-free succinimide baths were studied in this paper. The effect of pH on the electrochemical structure and electrochemical process were analyzed by electrochemical impedance spectroscopy (EIS). The reversibility of the bath with different pH was characterized by cyclic voltammetry (CV). The results showed that the electrodeposition process was irreversible in different pH baths. The highest polarizability and reversibility were observed at pH9 bath. The reason of highest polarizability at pH9 is due to the hydrolysis of succinimide and formation of NH3. The compositions of baths with different pH were measured by XPS, which confirmed the hydrolysis of succinimide and the singleness of silver ion's valence state. The nucleation process of silver at different deposition potentials that in the range of -0.4–0.7 V was studied by chronoamperometry. The comparison of dimensionless curves with Scharifker and Hills (SH) theoretical model showed that the nucleation of silver in bath was closer to instantaneous nucleation. The microscopic images of early nucleation were captured, which proved that nucleation was discontinuous and might interfere with each other. The nano-silver films were obtained by electrodeposition within the current density ranging from 0.4 to 0.7 A/dm2. The microstructure observed by scanning electron microscope (SEM). The results showed that grain size increased abnormally with the increase of current density and the silver film exhibited the finest grain size was obtained at the current density of 0.4 A/dm2. The phenomenon was caused by the instantaneous nucleation and the interaction between nucleation points.