Preparation And Properties Of Ni (OH) / Graphene Composites Reinforced By CNTs

Supercapacitors are a new class of energy storage devices, which have higher energy density than conventional capacitors, and larger power densityand longer cyclic life than batteries. But there still exist the shortcomings of low energy density and high cost. Research about supercapacitors is mainly focused on developing high-performance electrode materials.In this thesis, Ni(OH)2/graphene nanocomposites were prepared by a rapid microwave heating method, taking graphene and graphite oxide (GO) as substrate, respectively. By adding a small amount of carbon nanotubes (CNTs) to construct a more effective conductive network, the3D interconnected Ni(OH)2/graphene/CNTs nanocomposites were prepared. Preparation parameters such as solvent, adding rate of precipitation agent, pH value, ratio of Ni(OH)2to graphene, heating method, microwave heating time, content of CNTs and sedimentation time were investigated. Crystal structure and morphology of the composite were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM), and the electrochemical performance was tested by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvannostatic charge/discharge using a three-electrode system.Graphene was directly applied as substrate to prepare Ni(OH)2/graphene composite, CV results showed that:directly poured the NaOH precipitation agent, pH value of suspension was between9-10, microwave heating time was3min with a power of700W, the Ni(OH)2/graphene composite with20wt%of Ni(OH)2presented a specific capacitance of177.3F g-1at2mVs-1, when the mass of the electroactive material was3.7mg/cm2; the specific capacitance of the composite were210.2F/g and298.5F/g, when the content of Ni(OH)2increased to40wt%and80wt%, respectively; as compared to traditional heating method (refluxed in ethylene glycol solvent at150℃for4h, other reaction conditions were same), the specific capacitance of composite prepared by microwave heating increased by62.0F/g; with addition of CNTs, when the mass ratio of graphene to CNTs was1:1, Ni(OH)2/graphene/CNTs composite has a specific capacitance of259.8F g-1.Preparation of GO via hummers method, the Ni(OH)2/reduced graphene oxide (Ni(OH)2/RGO) composites were prepared by microwave heating method in ethylene glycol medium. Research demonstrated that:GO ultrasonic dispersing time was2.5h, microwave heating time was4min, the composite had a maximum specific capacitance of325.0F g-1, when the mass of the electroactive material was3.5mg/cm2. With addition of CNTs, when the mass ratio of GO to CNTs was3:1, Ni(OH)2/RGO/CNTs composite had a specific capacitance of361.5Fg-1.Electrochemical performance of Ni(OH)2/RGO/CNTs (GO:CNTs=3:1,GC3) composite was tested with the electroactive material mass of1.0mg/cm2. Results showed that:GC3had a specific capacitance of1029.3F g-1at2mVs-1and969.6F g-1at current density of0.5A g-1in6M KOH aqueous solution. Further, the specific capacitance retained92.1%after1000cycle tests at current density of5A g-1, indicating good cycling stability.