Insight into the role and mechanism of 2,2-bipyridine as a novel additive for nano-electrodeposition of Zn-Ni alloy

Abstract

Nanocrystalline Zn-Ni alloy is greatly significant in improving mechanism, corrosion and wear properties of conventional coarse-grained Zn-Ni alloy and it is usually formed by the synergetic effects of two or more additives. However, the multiple additives not only make the electrolyte complicate and unstable, but also difficult to analyze the effect mechanism of each additive during electrodeposition. In this work, nanocrystalline Zn-Ni alloy is deposited from an alkaline bath with 2,2-bipyridine as a novel additive. The electrochemical mechanism and effect mechanism of 2,2-bipyridine on the formation of nanocrystalline Zn-Ni alloy were investigated. It is noted that the presence of 2,2-bipyridine does not change the mixed controlled growth mechanism of Zn-Ni alloy, however the nucleation mechanism changes from instantaneous to progressive nucleation process with 2,2-bipyridine. The transfer coefficient α and diffusion coefficient D were also calculated by cyclic voltammogram and chronoamperometry. A significant increase of the Zn-Ni electrodeposition potential is observed in the presence of 2,2-bipyridine owing to the strong adsorption of 2,2-bipyridine on electrode surface, specially the synergistic effects of its nitrogen-containing group and ring structure, which is beneficial for increasing the free energy to form new nuclei, thereby resulting in a higher nucleation rate and smaller grain size.