Preparation of Three-Dementional Graphene-Based Hybrid and Its Application As Electrode Material in Spercapacitors

Author:Xiong Chuan Yin

Supervisor:li tie hu


Degree Year:2018





Supercapacitors,as environmentally friendly energy storage devices,have the advantages of high power density and low pollution.However,compared to batteries,such divices with high power densities own lower energy densities,which seriously restricts the commercial applications of supercapacitors as energy storage devices.Aim to broaden the scope of application of supercapacitors,it is very necessary to further improve the electrochemical performance of supercapacitors.Researchers have done a lot of work on low-cost,high-performance and environmentally friendly novel electrode materials.The three-dimensional(3D)graphene(GR)-based hybrid electrode materials fabricated by various methods not only effectively prevent mutual re-stacking between the GR layers to make full use of specific surface area of GR,but also obtain excellent electrochemical performance via introducing other functional materials.This paper developed a combination of floating catalysts chemical vapor deposition(FCCVD)and electrochemical approaches to fabricate 3D GR-based hybrid materials,including GR-,carbonaceous,metal oxide and conducting polymer materials,and utilize the synergistic effect among various components to improve the electrochemical energy storage performance of electrode materials.The nickel foam(NF)is served as the substrate to prepare 3D reduced graphene oxide(RGO)-carbon nanotubes(CNT)hybrid electrode material by a two-step method of a simple electrophoretic and FCCVD.In short,firstly,two NF sheets,treated with acetone and ethanol,are put into the graphene oxide(GO)solution of 2 mg mL-1 and connected with the positive and negative of a constant voltage source individually.Then the GO films with different thickness can be obtained by adjusting the deposition voltage and time.The following,the as-obtained GO-NF are used as a new template for the growth of vertically aligned CNT arrays on the surface or between the layers of GR by one-step FCCVD technique,thus obtaining 3D GR-CNT sandwich structure hybrid material.The as-prepared 3D composite can be used directly as electrode material of supercapacitors,and exhibits outstanding electrochemical properties.Pure carbon materials are still limited to enhance electrochemical performance of supercapacitors,especially for energy density.Furthermore,manganese dioxide(MnO2)was introduced into the RGO-CNT hybrid by electrochemical deposition.As we all know,MnO2can provide enormous pseudocapacitance,but poor conductivity.GR and CNT can compensate for the poor conductivity of MnO2,which realizes the complementary advantages of each component.Here,the titanium(Ti)sheets are acted as substrates for electrochemical deposition of MnO2 nanowalls.Then the Ti sheets covered with MnO2 nanowalls are served as new templates to load RGO-CNT hybrid according to the same procedure in the previous work,thus obtaining 3D GR-CNT-MnO2 hybrid.The as-prepared hybrid has an improved electrochemical energy storage performance when used as the electrode material of supercapacitors.The conductive polyaniline(PANI)not only has outstanding conductivity but also owns tremendous pseudocapacitance.Therefore,we further consider to replace MnO2 with conductive PANI to obtain 3D nanoporous GR-CNT-PANI hybrid.In short,based on the work above,controllable PANI nanorods or nanofibers are further deposited into the GR-CNT hybrid by electropolymerization.The as-fabricated hybrid not only presents porous property,which is beneficial to electrolyte transport and the contact between electrode and electrolyte,but also has a large specific capacitance,being a promising electrode material for supercapacitors.With the continuous emergence of flexible portable electronic devices,electrode materials should meet the requirements of lightness and flexibility.Based on this point,during the process of devising 3D graphene-based hybrid,we further fabricate 3D GR-based hybrid with flexibility to meet the growing needs of people.On the basis of previous work,we replace the NF substrate with flexible carbon fibers(CF),and then use the same craft to fabricate 3D light and flexible GR-CNT-CF hybrid elctrode material.The as-prepared hybrid not only has outstanding electrochemical energy storage performance but also shows excellent flexibility when used as the elctrode material of supercapcitors.