纳米结构黑镍薄膜的电沉积机理

ELECTROPLATING MECHANISM OF NANOSTRUCTURED BLACK Ni FILMS

采用直流电沉积技术在改性的Watt镀镍溶液中获得了纳米晶黑镍薄膜,采用SEM和XRD对薄膜的表面形貌和相组成进行了表征,采用循环伏安法和电化学阻抗谱对黑镍薄膜的初始电沉积行为进行了研究.结果表明,黑镍薄膜表面平整光亮,具有纳米晶结构;黑镍薄膜的电沉积过程遵循3D成核/生长机制;随着阴极沉积电势(负偏压)的增大,黄铜电极表面Ni的电沉积反应由UPD沉积、异质成核/生长转化为最终的同质成核/生长,相应的电荷转移电阻R_t的值先增大然后减小;在较高的阴极沉积电势作用下,由于吸附H原子(H_2分子)的结晶阻止作用和(镍)羟基化合物的吸附作用,电沉积EIS图出现低频和超低频感抗弧.

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 sub- sequently decrease of charge-transfer-resistance （R_t）.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.