ELECTROPLATING MECHANISM OF NANOSTRUCTURED BLACK Ni FILMS
纳米结构黑镍薄膜的电沉积机理

Nanocrystalline black nickel film has been obtained from a modified Watt bath by using DC (direct current) electroplating method, and characterized by using SEM and XRD. Meanwhile, the initial electroplating behavior of the nanocrystalline black Ni film was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that the black Ni film is substantially smooth and bright, and consists of particles with the mean size 51.4 nm. The deposition of black Ni film followed the mechanism of three-dimensional (3D) nucleation and subsequent grain growth. With the increase of the negative potential bias, the main deposition process of black Ni film onto brass changed from the under-potential deposition (UPD) through heterogeneous finally to homogeneous nucleation/growth, which consequently resulted in the initial increase and subsequently decrease of charge-transfer-resistance (Rt). At the high negative bias, the occurrence of the low and the ultra-low frequency inductive loops on EIS plots, can be attributed to the adsorptions of hydrogen atoms and the nickel hydroxyl compound onto cathode surface, which retarded the nucleation/growth process of nickel.