Preparation of 3D Carbon Material by Sol Gel Method and Research on Controlling Its Supercapacitors Performance

Author:Xu Feng

Supervisor:huang fu qiang


Degree Year:2018





Carbon materials especially activated carbon are commonly used as energy storage materials.However,the progress of life has high demand for energy storage materials,and activated carbon is difficult to meet this requirement,so we need new energy storage materials.Excellent energy storage materials should have good conductivity,high specific surface area,large pore volume capacity and suitable pore size distribution.Graphene is a new super material,it is also a research hotspot in the field of materials.It has characteristics of good thermal conductivity,large surface area and other excellent properties,but graphene is a two-dimensional material,its application prospect is limited.I have prepared three-dimensional graphene material through sol gel method conbined with CVD growth.This material has excellent electrical and thermal conductivity and can be widely controlled in structure which is a potential energy storage carbon material.In this thesis,based on the material structure,I designed and prepared three-dimensional few-layer carbon materials.Carbon materials were prepared by CVD method,and the energy storage properties were further improved by activation,doping and compounding.Several methods have been developed for the preparation of high-performance graphene materials on the originality of the material structure.The main achievements are as follows:Based on the traditional organic template method,a new inorganic-organic combination template method has been designed,through this method a variety of oxide with ordered macroporous structure could be fabricated.An independent,endogenous ordered macroporous graphene based on the inorganic-organic template combined with CVD method has been successfully fabricated.This graphene activated by ammonia during CVD process has good supercapacitor performance.Combining the template and the sol-gel method together I improved this inorganic-organic template method.With this new template,ordered macroporous carbon materials with different textures has been prepared.One of them has ordered IV square network structure,and this morphology is observed for the first time.So,organic-inorganic template method is not only a method for good performance macroporous carbon materials but also for microstructure controlling.The material prepared by this improved template method has a specific capacity of 415 F/g.A low-cost sol-gel route to a N-doped,albeit disordered,mesoporous graphene that maintains an extraordinary capacitance(690 F g-1)has been developed.The capacitance,which exceeds the theoretical limit of double-layer capacitance of carbon(?550 F g-1)and is several times the typical capacitance of commercial activated carbon(?200 F g-1),is mainly derived from redox reactions that are not limited by reactant diffusion.As-prepared few-layer carbon possesses a connected,disordered,hierarchical porous structure,and its electrodes can maintain 90% of its initial capacitance after 30,000 cycles.Such low-cost preparation may help pave the road for practical applications of N-doped few-layer carbon in high-energy-density electrochemical storage devices.I have combined the sol-gel route with low boiling point metals to fabricate nitrogen doped carbon materials with hierarchical pore structure based on silicon-zinc sol-gel.Zinc ions can form complexes with nitrogen source(pyrrole),so that during stirring or drying operations,pyrrole will not volatilize.In the process of CVD heating,zinc ions are combined with oxygen to produce Zinc Oxide and then be reduced to zinc metal.At the temperature near the boiling point(907 ℃),zinc will leave holes in the carbon material to increase the specific surface area of the material.The carbon materials prepared with the silicon-zinc sol-gel method have high nitrogen content(5.6 at.%),which has good electrochemical energy storage capacity(specific capacity 380F/g).The carbon materials prepared by sol-gel method have great supercapacitor performance.The reasons for this performance have been explored.The Si-O-Si network,formed in the preparation of silica sol,plays an important role in this process.It can not only make the carbon material form a complete three-dimensional network structure,but also make the active nitrogen atoms stable at high temperature.The prepared carbon materials can have high specific surface area,high conductivity and high nitrogen doping content at the same time,so carbon materials can achieve good electrochemical energy storage performance.