Study On Surface Modification Of Graphene And Properties Of Electrochemical Energy Storage

In the 21st century,the problem of energy shortage and environmental deterioration has become increasingly serious.We urgently need large amounts of clean and renewable energy materials and equipment,such as super capacitors,fuel cells,and aluminum ion batteries.The research of these energy storage devices is mainly focused on the electrode materials.However,because of the high conductivity and large specific surface area,graphene has great potential when use it as an electrode material for energy storage devices.In this paper,3D porous graphene materials,graphene/polydopamine and graphene/polyaniline composites were prepared and used as electrode materials for supercapacitors,fuel cells and aluminum ion batteries,respectively.We research the electrochemical energy storage characteristics of the electrode materials.The main content of this paper is:Preparation of 3D porous graphene materials and their energy storage properties in supercapacitors:we use the graphite oxide as raw material,preparation the 3D graphene materials by hydrothermal method,adjusting the pore structure of three-dimensional graphene by use CO2 as pore-forming agent to prepare three-dimensional porous graphite.The supercapacitor performance of the materials was studied.The prepared materials were characterized by SEM,BET,and XRD.The results show that after activation by CO2 with 60 min,the material has a good three-dimensional structure,large specific surface area and stable microporous structure.Electrochemical tests show that when the activation time is 60 min,the capacitance is the best,the specific capacitance can reach 80 F g-1 when the current density was 2 A g-1,and it has very good rate performance,so the quick charge and discharge could be achieved effectively.The Materials shows the great potential in supercapacitors.Preparation and electrocatalytic performance of graphene/dopamine composites:The graphene/polydopamine composites were synthesized by in-situ polymerization method by use graphene as a substrate and dopamine as a nitrogen source.Through a series of characterization methods such as SEM,TEM,XRD,FTIR,Raman,XPS,etc.,the change of morphology,structure and surface properties in the composite process of materials was studied.It is proved that the dopamine partially reduced graphene in the in-situ polymerization process,and some defective carbons and some new and different types of nitrogen-containing functional group was formed at the same time which provided more active sites.Electrochemical tests show that the composites have good electro catalytic activity in terms of starting potential,numbers of electron transfer,and limiting current density.The optimized graphene/polydopamine composites have better electrocatalytic activity than N-doped graphene.In addition,compared with thr commercial Pt/C catalysts,graphene/polydopamine composites have excellent stability and methanol resistance,which is beneficial to their application in alkaline fuel cells and direct methanol fuel cells.Preparation of graphene/polyaniline composites and their application in aluminum ion batteries:Graphene and aniline are used as raw materials,the graphene/polyaniline composites are prepared by freeze-mixing.The characterization of SEM shows that the thickness and morphology of composites can be effectively changed by adjusting the mass ratio of graphene and aniline.Electrochemical tests show that different thicknesses and morphologies will have a great influence on the electrochemical performance of the material.When the mass ratio of graphene to aniline is 1:8,the composite material has good electrochemical performance,after 3,000 cycles,the mass specific capacitance can reach 163 mAh g-1 when the cutoff voltage was 2.3 V.It also has good cycle performance and reversibility.The materials can be well applied in the field of energy storage for fast charging and slow discharging because of the outstanding rate performance.We believed that after further investigation of the mechanism and structural optimization,the material is expected to be applied to the commercial aluminum ion batteries.