Preparation And Electrochemical Performance Of Cobalt Hydroxide(Oxide)/Carbon Nanotubes Paper Flexible Composites

Electrochemical supercapacitor is a new type of energy storage device betweenstatic capacitor and secondary batteries. In recent years, because of their high powerdensity and long cycle life, supercapacitors have attracted great interest inelectrochemical energy storage applications. Pseudocapacitive cobalt hydroxides(oxides) are promising for next-generation supercapacitors due to their hightheoretical specific capacitance (SC), good electrochemical reversibility andenvironmentally benign nature. However, since cobalt hydroxides (oxides) have badelectronic conductivity, the peudocapacitors with such electrodes invariably sufferfrom low capacitance and poor rate capability at high current densities. Based on theabove analysis, we reviewed current cobalt-based oxides/hydroxides research andapplication. Used high electrical conductivity of carbon nanotubes paper as thesubstrate, combined with a variety of emerging nanomaterials preparation means tobuild a series of novel morphology and microstructure of cobalt-basedoxides/hydroxide flexible composite and their electrochemical performance wastested and Systematicly evaluated the relationship between the Synthesis of thematerial-the Micro-structural features-Growth mechanism-the Electrochemicalperformance. The main studies are as follows:1. Uniform hierarchical flower-like β-Co(OH)2anchored on conducting carbonnanotubes (CNT) papers were successfully synthesized by hydrothermal method. Thestructure and morphology of the products were studied by X-ray diffraction (XRD)and scanning electron microscope (SEM). Three dimensional (3D) loosenano-flowerlike structure were stacked by multilevel β-Co(OH)2flakes. Theelectrochemical properties of composite materials served as a high-performanceelectrochemical capacitor flexible electrode were tested. Electrochemical dataindicated that the interesting β-Co(OH)2/CNT paper composites obtained an obviousimprovement of rate capacity and cycling stability compared with pure phase β-Co(OH)2.2. Co3O4and Co3O4/CNT paper flexible composite are successfully synthesizedby thermal conversion of their precursor in the presence of nitrogen gas, which can beobserved that the morphology of the precursors can be better maintained by scanningelectron microscope (SEM). The as-prepared Co3O4/CNT paper flexible compositewas characterized by Brunauer-Emmett-Teller (BET) N2adsorption, the resultindicate that the as-synthesized material has a porous structure, which specific surfacearea is180m2/g, aperture is5nm.. Electrochemical data indicated that theCo3O4/CNT paper composites delivered SC of the40th lap of1442F/g at1A/g. It isnotable that the SC of the Co3O4/CNT paper flexible composite is up to1526F/g after1500continuous charge-discharge cycles. This Co3O4/CNT paper composite exhibitedexcellent cycle performance as a supercapacitor electrode compared with theprecursor composite.3. Uniform porous honeycomb-like α-Co(OH)2were potentiostatic depositedonto EA-CNT paper which treated by nitric acid reflux purifying and electrochemicalactivating for electrochemical capacitor application. The surface morphology andmicrostructure of the composites were characterized by X-ray diffraction (XRD) andsanning election microscopy (SEM). The growth mechanism of poroushoneycomb-like structure film material was discussed. The effects ofelectrodeposition time and different substrates (Ni substrate) on the microstructureand electrochemical capacitance performance of prepared porous α-Co(OH)2filmwere systematically studied.4. Co3O4/EA-CNT paper flexible composites films are successfully synthesizedby thermal conversion of the precursor with the best deposition time for30mins.Co3O4/EA-CNT paper flexible composite film materials can better keep the precursormorphology of3D honeycomb-like network structure. Electrochemical data indicatedthat the paper-like flexible composite film delivered a high SC of1300F/g at current density of1A/g. Furthermore, the SC degradation of only4%after1,500continuouscharge-discharge cycles at1A/g demonstrates its good electrochemical stability.5. Using EA-CNT paper as the conductive substrate, different morphologys of theflexible composite film material were successfully preparaed by usingpotentiodynamic scan method by controling different scanning speed. Also weinvestigate the influence of the morphology, growth mechanism and electrochemicalproperties of the flexible composite film materials at different scanning speeds.Bloomy flower-like α-Co(OH)2film strongly anchored on EA-CNT papers weresuccessfully obtained at scan rate of20mV/s. These three dimensional (3D) loosenano-flowerlike is composed of interconnected multilevel two-dimensionalα-Co(OH)2nanoflake open system which self-assembly built. Electrochemical dataindicated that the α-Co(OH)2/EA-CNT paper flexible composite film delivered aconsiderable SC of1856F/g at current density of1A/g, and a good rate capacity,after1500cycles,80%of initial capacitance remains.