Synthesis And Electrochemical Performances Of Ni/NiO Core-shell Materials

In recent years, with the massive growth of energy pollution problems and the need of portable electronic equipment are increasingly serious,super capacitor has become a hot research of new chemical power sources, for the factor that supercapacitor show both high power density and high energy density and physical capacitor conventional batteries,the transition metal oxide is the most notable Faraday pseudocapacitive electrode materials, the electrode material is the the decision factors of pseudocapacitive capacitance performance. So far, the electrode materials include oxides of transition metals. (RuO2,MnO2, NiO, CoO, CuO, etc.) and hydroxide (Ni (OH)2,Co (OH)2, Cu (OH)2,etc.),Conducting polymer (polypyrrole). The capacitance properties of RuO2 in transition metal oxides are excellent .However, due to its high cost limits its large-scale commercial applications, NiO not only has excellent electrochemical properties, theoretical capacity is 2573F/g,but also rich in natural reserves,environmentally friendly,very suitable for the application of supercapacitor. Recently, the studies on the metal / metal oxide shell of NiO have been reported; Lu and other mechanical polishing to form Ni metal particles, then the surface of the Ni metal particles was directly oxidized to form the core-shell structure of Ni/NiO nanoparticles, since the inner metal core replaced the metal oxide core, the conductivity of the electrode material and the collector fluid is enhanced, this facilitates the transmission of electrons in the oxidation process, therefore, it has good performance,high cycle stability, high energy density and power density, and high rate performance,however, the preparation of nano particles will increase the contact resistance between the active material and the substrate, and the binder will also reduce the utilization of the material and the process is more complex. In this thesis, we use a simple and mild method to direct the growth of NiO nano arrays on the surface of the nickel substrate, the Ni element was prepared on the substrate of Ni net, and then oxidized to form Ni/NiO core-shell structure, we explored the effect of hydrogenation process in different annealing temperature and annealing time on the electrochemical performance of the oxidation effect of temperature on the thickness of the NiO shell of different processing, obtained the Ni/NiO core-shell composite porous connection excellent performance in,the specific research work is as follows:(1) With simple and mild method of preparation of electrochemical performance of Ni/NiO core - shell material: will the growth of the hydrothermal Ni (OH) 2 nano piece of array in the air get NiO 2h 350 ? annealing treatment after array the NiO nano piece in hydrogen respectively in different temperature is 250 ?, 350 ?, 450 ? annealing treatment 2h and under the temperature 350?,respectively in different time of 0.5 h,2 h,4 h annealing treatment, get the sample of the natural cooling to room temperature.Using XRD, SEM, TEM, HRTEM, XPS and electrochemical tests on the material of the structure,morphology and the electrochemical properties were studied.Results show that in the hydrogen annealing treatment 2h at 350 degrees for Ni/NiO core - shell the electrochemical properties of nanomaterials is best, the specific capacitance of 533.33 F/g (current density of 1 a/g), after a 4000 - cycle can still retain 89.6% of the specific capacity.Ni/NiO core -shell composite material has the following characteristics: (?) Ni/NiO core - shell nanocomposite metal core to promote electron transfer in the process of REDOX reaction,and the (?) the NiO shell is very thin, helpful for better reaction of electrode materials.(2) Explore the oxidation temperature of Ni/NiO core - shell structure: the influence of the thickness of the NiO shell layer will NiO nanoparticles array in the hydrogen gas to 350?, 2 h after processing the sample in air respectively in different temperature 50 ?,150?, 250?oxidation treatment 1h, obtained the NiO shell thickness different Ni/NiO core - shell nanomaterials.Using XRD, SEM, TEM, HRTEM, XPS and electrochemical testing methods on the morphology of materials, NiO shell thickness and electrochemical properties were studied.The results show that with the increase of oxidation temperature of Ni/NiO core - shell nanomaterials NiO in the thickness of the shell is also increasing,temperature at 150 ? in air oxidation treatment 1 h to get the sample of the electrochemical performance of the best, under the current density of 1 A/g of specific capacitance of 1273 F/g, 10 A/g of constant current charge and discharge current density after 4000 times still can keep 91.9% of the specific capacity.