Studies Of Two Typical Systems Of Ni And Zn Electrodeposition

Electrodeposition has become an major means in modern surface sciences due to its advantanges in the preparation of the surfaces with special structure and functions. In this thesis, two typical electrodeposition systems were studied to obtain the Ni and Zn deposited layers with well-defined microstructure. On these bases, we also explored possible applications of these two types of materials.A major part of this M.Sc work was focused on the electrodeposition of mesoporous metal film. Mesoporous metal, with high specific surface area and highly ordered nanoporous, is of considerable interest for applications in electrochemical catalysis, batteries, fuel cells, super electrochemical capacitors and electrochemical sensors. The preparation and application of mesoporous metal has been a highlight in the research of nanomaterials. In recent years, template electrodepositions of different mesoporous metal particles or films in various surfactant aggregate systems, such as in hexagonal liquid crystal phase, reverse hexagonal liquid crystal phase and etc, are actively studied due to its operating simplicity and extensive suitability of this technique. For example, the templates are very cheap, and can be built easily to tailor the resulting materials well, and also, the size of as-prepared materials can be controlled by adjusting the geometric features of the templates. Particularly, the electrodeposition can be operated at room temperature without requirements of severe experimental conditions. In this thesis., mesoporous nickel films were prepared by electrodeposition using the templates of two different hexanagol liquid crystal phases of non-ion surfactant/H₂O/NiSO₄ ternary systems. In addition, the applications of the resulting materials in the electrochemical catalysis and electrochemical energy storage are demonstrated.In the other part of this thesis, the growth kinetics of zinc dendrite in the electrodeposition was studied using fractal method. Since zinc is widely used for many brances of electrochemical industries and the surface morphology of zinc plays a critical role in these applications, it is of great significance to obtain a deeperunderstanding and a clear description of the dendrite growth of zinc.In summary, the main experimental results and conclusions of this M.Sc work are as follows:1. The phase transition temperature and optical texture of the ternary mixtures of liquid crystal template systems were investigated by differential scanning calorimetry (DSC) and polarized light microscopy. The weight proportions of the two different non-ion surfactants to form the hexanagol liquid crystal phases were determined to be 47% and 55% respectively for Cit,EO|0 and CisEOio- The electrochemical properties of the hexanagol liquid crystal phases were evaluated by use of cyclic voltammetry and amperometric i-t curve. Based on this study, we developed a simple method to obtain a mesoporous nickel film onto the Au electrode by electrodeposition of Ni ions from the hexanagol liquid crystal phases.2. The transmission electron microscope studies has revealed that the liquid crystal phase used in this synthesis works as a template and the resulting nickel film is very loose and porous with irregular nanostructured pores. The cyclic voltammogram in a 0.5M NaOH solution showed that the resulting Ni film has a very high specific surface area and can be applied as a electrocatalytic cathode for hydrogen evolving and a working electrode for super electrochemical capacitors.3. The diagram of morphologies for zinc growth under different ZnSC>4 concentration and different cell voltages were measured in the two-dimensional electrodeposition. It is found that the dendrite morphology generally grows in the moderate concentration and high applied voltage. Meantime the concentration distribution of Zn2+ ions and voltage in the thin electrolytic cell were also measured. Based on these results, we discuss the diffusional transportation behaviors of Zn f and the screening effects of the dendrite formation of Zn on the successive growth of Zn in the two dimensional electrodeposition. Under the condition of dendrite growth, the influences of support electrolyte, surfactant and pulse potential on the morphology and growth behavior of zinc have been e\aluated. The results indicate that the support electrolyte, surfactant and pulse potential can remarkably change morphologies of zinc growth by changing the distribution of Zn2f concentration and the strength ofelectric field at the cathode. In addition, It was also found that the immigration of Zn2"1 ions is only realized by electromigration and the contribution arising from Zn21 diffusion can be neglected.