Study On The Preparation And Electrochemical Performance Of Layered Double Hydroxides And Metal Oxide

Since the electrode material is one of the key factors in influencing the capacitiveperformance of supercapacitors, it is significant to develop the design of electrodematerial for supercapacitors. The aim of this research focuses on exploring the use ofcheap raw materials and facile synthetic techniques for synthesizing high specificcapacitance of Co/Al LDHs, Ni/Co LDHs, NiCo2O4, Bi2O2.33and Bi2O3/Mn3O4composite, which are used as the electrode materials of supercapacitors. Variouscharacterization methods are employed to characterize and analyze their structure,morphology and performance. The major contents can be summarized as follows:(1) Porous Co/Al LDHs nanoparticles were prepared by hydrothermal synthesismethod at different pH conditions. The structure and morphology of the obtainedmaterials were characterized by X-ray diffraction (XRD), N2adsorption-desorption,Fourier transform infrared spectrometer (FT-IR), scanning electron microscopy(SEM), transmission electron microscopy (TEM) and high-resolution transmissionelectron microscopy (HR-TEM). The mechanism for formation process of Co/AlLDHs nanoparticles was studied. The cyclic voltammetry (CV), galvanostaticcharge-discharge curves and electrochemical impedance spectroscopy were employedto study the electrochemical performance of the Co/Al LDHs nanoparticles. Theexperimental results reveal that the specific capacitance of the hydrotalcite materialprepared at pH13is up to376F/g, and the capacitance retains up to83%after1000cycles.(2) Ni/Co LDHs nanosheets with porous cross-linked structure were synthesizedby reflux route using water-ethanol as solvent. The morphology of the Ni/Co LDHsprepared at different reaction time was discussed. The effect of the different nickelnitrate/cobalt nitrate molar ratio on the electrochemical performance was investigated.The electrochemical data indicate that the Ni/Co LDHs electrode has a predominantspecific capacitance and large current charge-discharge performance. The specificcapacitance of Ni/Co LDHs reaches to1537F/g under the current density of0.5A/g,and it still maintains1181F/g when tested at10A/g. Moreover, the capacitanceretention at2A/g discharge current condition is80.3%after1000cycles, suggests theexcellent reversibility of this Ni/Co LDHs material. The specific capacitance of theporous NiCo2O4nano nanosheets obtained by heat treatment for the Ni/Co LDHs is756F/g. (3) Bi2O2.33for electrode material of supercapacitors, which possessed exellentelectrochemical performance, was prepared by a facile chemical coprecipitation incombination with heat treatment method. By controlling the Bi3+/tetrabutylammonium bromide (TBAB) molar ratio, the pure and well-dispersed Bi2O2.33microspheres were obtained, which consists of radial nanosheets. These microsphereshave diameters of3~5μm, whose interior structure owes many channels (~1.1nm).This unique interior structure helps to promote electrolyte penetration, resulting in arapid reversibility of redox reaction at the interface between electrode and electrolyte.Thus, the electrode material significantly increases the specific capacitance. Under thecurrent density of0.1A/g, the specific capacitance of the Bi2O2.33material is up to891F/g, and the capacitance only losses4.0%1000cycles. The as-prepared materialhas an excellent capacitive performance and good cycling stability, which is apromising electrode material for supercapacitors application.(4) The simple solvothermal method was adopted to synthesize Bi2O3/Mn3O4composite. The structure and morphology of the composite were characterized viaXRD, inductively coupled plasma (ICP) and TEM. The application in electrochemicalcapacitors of the composite was also investigated. It shows that the Bi2O3/Mn3O4composite displays good synergy effect between Bi2O3and Mn3O4, and its specificcapacitance is as high as707F/g, which is9times than that of Mn3O4electrode (78F/g).