Research On Three-Dimensional Graphene-Metal Organic Frame Derived Carbon Composites For Supercapacitors

The structure of fuel supply determines that thermal power generation is the main power supply way in our country,and the electricity system is immediate,the electric energy only be used immediately and cannot be stored,which wastes a lot and makes huge environmental damage every year.Therefore,people's demand for high-performance energy storage equipment is getting higher and higher.Because of its advantages of fast charging rate,long cycle life and low maintenance cost,supercapacitors are regarded as new opportunities to solve future energy storage problems.Therefore,the research of electrode materials of supercapacitors has received extensive attention.Graphene is a two-dimensional carbon material with one atom thickness.It has huge specific surface area.The theoretical specific surface area of graphene is up to 2630 m2/g,which is more than twice of the theoretical specific surface area of activated carbon.Moreover,its stable structure and six-membered ring structure endow it with excellent mechanical properties including large spring constants and high Young's modulus values.Therefore,much attention has been paid to graphene-based electrode materials for supercapacitors.However,due to the fact that graphene itself is easy to aggregate,its speci fic surface area is greatly reduced,which also leads to the poor capacitive performance of graphene itself.In this work,we prepared three-dimensional(3D)graphene aerogel materials with abundant macropores and mesopores structure by hydrothermal method using graphene oxide as the raw material,which avoided the agglomeration of graphene.In regarding to the problem of low capacitance of single graphene materials,this paper designed a 3D graphene-metal organic framework derived carbon composite material with hierarchical pore structure.Graphene aerogels acted as the substrates and ZIF-8 in situ grew on its surface through layer-by-layer loading process.Interconnected micro-meso-macroporous structures were formed after high-temperature carbonization.Such structure improved the specific surface area and optimized the pore distrubution of graphene aerogels.This work systematically studied the influence of specific surface area and pore size distribution towards the resultance capacitive performance.Through the two electrode system,the application potential of the 3D graphene-metal organic framework derived carbon composite material was evaluated.Study details are listed as follows:(1)Microstructure and capacitive properties of three-dimensional graphene aerogelIn this paper,graphene oxide was used as the raw material and self-assembled by hydrothermal method under the reduction of ascorbic acid,forming three-dimensional structure.Compared with ordinary graphene,three-dimensional graphene aerogel has better mechanical properties and higher stability.By calcination at high temperature,its reducibility is improved and its conductivity is greatly improved.(2)Microstructure and capacitive properties of metal-organic framework derived carbonIn this paper,ZIF-8 crystals were synthesized,and the carbon derived from ZIF-8 was formed by calcination at high temperature for a long time.During the calcination at high temperature,some mesoporous structures were introduced into the microporous structure of ZIF-8 crystals,which improved the pore structure and the ion migration rate.(3)Fabrication and capacitive performance of 3D graphene-metal organic framework derived carbon composite with hierarchically porous structureIn order to improve the capacitive performance of 3D graphene,this work utilized the method of cyclic loading.ZIF-8 crystal in situ grew on the surface of graphene aerogels.Through high temperature calcination,hierarchically porous structure with the coexistence of macropores,mesopores and micropores formed.The electrode materials with high specific surface area and optimized pore size distribution.3D graphene-ZIF-8 derived carbon composite displayed remarkable specific capacitance of 409.5 F g-1 at 1 A g-1.With current density increasing from 1 A g-1 to 10 A g-1,the specific capacitance was 288 F g-1,retaining 70%of the orignical value.Furthermore,after 1000 galvanostatic charge-discharge cycles at 5 A g-1,this material showed an excellent cycle stability with 97.3%maintaintion of the original capacitance.