Preparation And Electrochemical Property Study Of Hierarchical Pore Structure And Nitrogen-doped Graphene-based Aerogels

Graphene aerogel is often used as an electrode material of supercapacitors for electrical automotive and rail transportation due to its low density,high porosity,high specific surface area and excellent electrical conductivity.The key factors that affecting the electrochemical performance of graphene-based aerogels are specific surface area,active sites concents and the transport efficiency of ion/electronic,and by constructing a hierarchical pore structure,high specific surface area,electrochemically active sites concents,and ion/electronic transport efficiency of the aerogel can be simultaneously improved.In addition,doping nitrogen into the graphene skeleton and introduction of nano-carbon structures can improve its electronic properties and further improve the electrochemical performance of aerogels.Hydrothermal method,due to its simple and productive operation,is often used to prepare graphene-based aerogels.But till now,there are few reports on how to construct a hierarchical pore structure and how to introduce nitrogen element and nano-carbon structures during the hydrothermal reaction.Therefore,how to choose the types of nitrogen dopants,nano-carbon source and the construction of aerogel hierarchical pore structure has been considered and designed in this paper,hierarchical pore structure and nitrogen-doped graphene-based aerogels was prepared by using graphene as the framework,chitosan as the nitrogen source and resorcinol-formaldehyde?RF?as the nano-carbon source,the electrochemical properties of aerogels was explored by electrochemical testing methods.The research contents mainly include the following aspects:?1?Preparation and electrochemical performance of aminated graphene-based aerogelsFour types of graphene-based aerogels with different chitosan contents were prepared by controlling the mass ratio of graphene oxide and chitosan.It was found that the chitosan can prevent the close-packed of graphene sheet effectively during the hydrothermal process.When the mass ratio of chitosan to graphene oxide is 1:4,the prepared CGO4 has a hierarchical pore structure with a specific surface area reached 616 m²/g,and the saturated adsorption capacities of CGO4 for Cu²⁺and Pb²⁺reached up to 342.4 mg/g and 945.1 mg/g respectively after amino modification by chitosan.The electrochemical performance of CGOs was evaluated by electrochemical tests.Results showed that the electrochemical performance of aerogels is affected by the specific surface area,pore structure and active sites contents.CGO4 has the highest specific capacitance?105.5 F/g?,its specific capacitance can reserved 75.6%after 2000cycles.?2?Preparation and electrochemical performance of nitrogen-doped graphene-based aerogelsNitrogen-doped graphene-based aerogels were prepared by thermal annealing of CGOs.The prepared NCG4 still retained a hierarchical pore structure,with the highest specific surface area?1381 m²/g?and nitrogen contents?1.25 at%?.The electrochemical performance of NCGs was evaluated by electrochemical tests.Results showed that the aerogel's electrochemical performance was affected by specific surface area,pore structure and nitrogen concents.NCG4has the highest specific capacitance?223.3 F/g?,good frequency doubling characteristics,its specific capacitance can reserved 93.1%after 2000 cycles.?3?Preparation and electrochemical performance of nano-carbon modified nitrogen-doped graphene-based aerogelsThe nano-carbon modified nitrogen-doped graphene-based aerogels were prepared by introducing RF-based microstructured carbon into the graphene skeleton.It was found that when the mass fraction of RF was 0.5 wt%,the prepared CRF1-NCG retained the hierarchical pore structure while the nitrogen content was further improved?1.46 at%?and the specific surface area was 912 m²/g.The electrochemical performance of the CRF-NCGs was evaluated by electrochemical tests.Results showed that the electrochemical performance of the aerogels were still affected by specific surface area,pore structure and nitrogen concents,especially in nitrogen concents.CRF1-NCG has the highest specific capacitance?276.9 F/g?,and better frequency doubling characteristic,its specific capacitance can be reserved 94.9%after 2000 cycles.