Fabrication And Performance Of Nano/micro Structures On Metallic Substrates As Electrode Materials

Energy storage is the fundamental problem of new energy development, while the development of energy storage device depends largely on the progress of new materials. The properties of the materials are closely related to its structure. Therefore, the development of facile and effective methodologies for rational control over the morphologies and size of the nanostructures are the prerequisite for practical applications in micro-electronic devices, energy storage and conversion. As to an advanced supercapacitor device, the preparation and modification of the electrode materials is the key now. How to find and prepare a desirable active electrode material with high capacity performance is the most important to optimal device performance. The paper focuses on the design and controlled synthesis of nano/micro structures on metallic substrates as electrode materials. Because this structure not only has the large surface area as the general film structure, but also has regular and ordered electrical channel, and could form strong electrical and mechanical contact with the sunbstrate materials. At the same time, we optimize its preparation method and improve the utilization of material and study their electrochemical performance.We explore the using Ni instead of Ru as electrode material. The simple synthesis system composed only of water, Ni(NO₃)₂ and NaOH, the effects of synthesis conditions, including nickel raw materials, precipitating agent, reactants molar ratio, reaction temperature, reaction time, are investigated in detail. We identified optimal reaction conditions. In order to improve the utilization of electrode materials, we control the reaction conditions by hydrothermal treatment, make the process of the formation of Ni(OH)₂ precipitation and the deposition on nickel foam simultaneously. Such deposit has strong absorption and could increase the effective utilization of active material due to the high temperature and pressure in the hydrothermal process. At the same time, it avoids the traditional complex process of the forming of electrodes by the re-pressed process on the nickel foam with additives, carbon black and binder. We investigated the electrochemical properties of the prepared material by cyclic voltammetry and constant current charge-discharge test. The results show that the effective utilization of the unique Ni(OH)₂ structure helps improving the electrochemical capacitance behavior, and the as-fabricated Ni(OH)₂ electrode displays a maximum specific capacitance as high as 1778 F g^-1 at a current density of 0.25 A g^-1 in 2 M KOH electrolyte. NiO is final obtained by calcination the as-prepared Ni(OH)₂ in muffle furnace at high temperature,which can also be used as electrode materials for application in supercapacitors.In our cetyltrimethylammonium bromide (CTAB)/sodium dodecyl sulfate (SDS) mixed cationic and anionic surfactants system, ZnO nanosheets and nanoplates are obtained by directly oxidation of zinc foil surface in peroxydisulfate (APS) alkaline solution and ethylenediamine (en), respectively,by using zinc foil as both zinc source and substrate. A series of control experiments show that many reaction parameters, such as surfactant types, hydrothermal temperature and concentration of reactants have a direct influence on the morphologies. The reason that ZnO nanostructures obtained in different reaction medium (NaOH and APS or en aqueous) possess different morphologies is because of different surface oxidation process. In addition, the CTAB/SDS mixed cationic and anionic surfactants system can be used as structure-directing agents or capping agents to modulate the growth of nano-materials by their synergy. Finally, Raman, photoluminescence and electrochemical test are used to characterize the obtained products.In CTAB/SDS mixed cationic and anionic surfactants system, Cu₂O nano/microstructures were grown directly on copper foil substrates by controlled surface-oxidation in APS alkaline aqueous solutions, by using copper foil to serve as both copper source and substrate. A reasonable formation mechanism was proposed based on the experimental results, and photoluminescence and electrochemical test are used to characterize the obtained products. According to the reaction principle that copper foil can be used as copper source, we explore the direct formation of copper sulfide on the surface of the copper foil. Cu₂S nanostructures are obtained via a facile one-step hydrothermal process using en and distilled water as co-solvent and CTAB as surfactant. To our surprised, Cu₂S nanosheets and hexagonal nanoplates have been synthesized respectively on either side of a copper substrate. This difference is mainly caused by different growing environment. In addition, we also examined the effect of the amount of solvent, adding other copper source, pH value on the morphologies of Cu₂S nanostructures.We have further explored the simple method to directly generate nano/micro structures on the surface of metal substrate. According to the principle of galvanic displacement, through a simple synthetic system, that is composed only of Zn and AgNO₃ solution , Ag nanostructures with different morphologies have been synthesized on the surface of zinc substrate. The experimental results confirm that synthesis routes, that are solution-dropping and solution-immersion, have direct influences on the morphologies of Ag nanostructures. We made a detailed comparison of the growth process and form mechanism. Then the two synthesis routes have been modified, respectively. The process of solution-dropping is modified by suitable thermal treatment,and for the process of solution-immersion, controlled reaction process could be achieved by introducing various additives to reduction reaction rate. The obtained Ag nanostructure could serve as excellent active substrate material for SERS detection of low concentration target molecules.Based on the research in this thesis, synthesis of nano/micro structures on metallic substrates as electrode materials, through the regulation of morphology to optimize its performance, particularly in electrochemical performance, several conclusions are drawn in the following:(1) For the synthesis of nano/micro structures on metallic substrates, this easy way that by the direct growth of hydroxide, oxide and sulfide on corresponding metal surfaces, provides the experimental basis for practical device applications.(2) The surfactant with amphiphilic molecules properties can be used as soft template in solution to form amphiphilic molecular assembly by self-polymerization, it can also prevent particles aggregation due to its steric effect of the long molecular chain, and play the role of stabilizing agent, dispersing agent, control and guidance functions. When the reaction system has the ligand with strong coordination ability, they could complex with metal atoms and adsorbed on the surface of the nanocrystal, which play a similar role as the amphiphilic molecules.(3) The essence of the galvanic displacement is active metal can replacement out the non-active metal from its salt solution.