Synthesis And Properties Of Electrode Cobalt Materials For Supercapacitor

Supercapacitor have been recognized as unique new energy storage devices which filled the gap between traditional capacitors and batteries. Due to the advantages of fast charging capability, high power density, and long cycle life. Supercapacitors have been used in electric cars, mobile communications and other fields. The application of supercapacitors have been limited because of its energy density. It has been a big challenge to improve the density.To boost the specific capacitance of supercapacitors, the specific surface area of the electrode materials needs to be as high as possible to accommodate a large amount of superficial electroactive species to participate in faradaic redox reactions. Cobalt oxides are one of the most important materials in nanotechnology because of their potential applications. Although catalysis, supercapacitors, and magnetic properties have been extensively studied in the recent years, the growth mechanism of various cobalt oxides nanostructures, the dependence of properties on structures, and the properties mechanism are still not clear. In the thesis, the growth mechanism, supercapacitance and the magnetic properties are studied. The main contents are summarized as follow.(1) We investigate the growth of cobalt hydroxide nanosheets as a precursor. Diameter-adjustable cobalt hydroxide nanosheets are synthesized by a facile and environmentally friendly hydrothermal route using deionized water as solvents.Scanning and transmission electron microscopy as well as various spectroscopic techniques show that the thickness of nanosheets is about 15nm. According to previous work and summing up the growth conditions, we propose a possible growth mechanism. Citrate with cobalt ions are combinated by the hydroxide in strong alkaline conditions. According to the stereochemistry of coordination particle, they have the choice of aggregate growth in low energy. Ultimately cobalt oxide nanosheets are formed in the orientation of the crystal lattice.(2) We study the porosity in cobalt oxide (Co3O4) formation mechanism. The porous Co3O4 have been formed by calcinating cobalt hydroxide nanosheets. In the growth process, the dehydration reaction and atomic diffusion process are importantly influenced on the final pore.(3) A wide range of Co3O4 nano shapes has been synthesized by calcination of Co(OH)2 nanosheets. We survey the morphology transitions, crystallinity (single-to poly-to single-crystalline again), porosity, and electrochemical capacity in the whole calcination temperature range from 200 to 900 ℃, all from one precursor in order to distinguish the influence of shape and porosity. We find that further optimization for supercapacitor applications should focus on the maximally porous structure gotten by 300℃ calcination. After a steep capacitance decline due to loss of pore access, the capacitance declines surprisingly linearly with 0.65 F/(g℃) over 500℃. This decline is dominated by the changing shapes (hexagon, ring, kidney, and sphere) with only 39% being due to lost porosity.(4) We investigate the growth of Ag doped cobalt hydroxide micro flowers. Diameter-adjustable microflowers are synthesized by a facile and environmentally friendly hydrothermal route using deionized water as solvents.