Research On Preparation And Electrochemical Performance Of Bamboo Cellulose-based Carbon Aerogel Composites

Cellulose carbon aerogel is an excellent substrate material because of its adjustable pore structure,high specific surface area and good electrical conductivity.However,it still has the problems of low specific capacitance,low energy density and poor surface wettability during its application in supercapacitors.In this paper,the electrode structure was reasonably designed and nitrogen-doped bamboo cellulose carbon aerogel with porosity and softness was prepared by using bamboo pulp fibers and the NaOH/urea dissolution system through one-step carbonization,activation and doping.The problem of poor surface wettability when carbon aerogel is used as matrix material was solved.On this basis,the ternary composite carbon aerogels with good stability,large specific capacitance and high magnification performance were successfully synthesized by composite graphene and MnO₂.By adjusting the process parameters,the interaction relationship among the physical structure,physicochemical properties and electrochemical properties of the composite carbon aerogel was analyzed,and the synergistic effect among N atom,graphene and MnO₂ was realized.The main conclusions of this research are summarized as follows:（1）A nitrogen-containing and hierarchically porous carbon aerogel was developed successfully from renewable bamboo cellulose through a one-step process.Sodium hydroxide and urea played the role as a solvent,active agent and nitrogen source combined.The formation,pore structure and N-doped content of carbon aerogels were controlled though the replacement times of deionized water during the regeneration and the pyrolysis temperature.Owing to the reasonable hierarchical porous structure(1017 m² g^-1 specific surface area)and nitrogen-doping content（9.51%）,the cellulose carbon aerogels which prepared with 5 times of substitution and 700°C exhibited the best electrochemical performance.It displayed a high specific capacitance of 153.3 F g^-1 at 20 A g^-1,retaining 76.5%of that at 0.5 A g^-1(200.4 F g^-1).（2）Graphene composite bamboo cellulose carbon aerogel was successfully synthesized by simple“mixing-gel-pyrolysis”method,after adding graphene oxide into bamboo cellulose solution which dissolved in NaOH/urea solution.The amount of graphene incorporation was closely related to the microstructure,graphitization degree and bonding form between atoms of the composites.When the mass ratio of graphene oxide to bamboo pulp fiber was 3%,graphene flakes and fibrous carbon were tightly combined to form a lamella structure,and the lamellas are arranged in parallel.Due to the good electrical conductivity(3.95 S m^-1)and a reasonable hierarchical porous structure（pore size range of 2～5.7 nm）,it demonstrated a high specific capacitance of 177.8 F g^-1 at 50 A g^-1,retaining 78.3%of that at 0.5 A g^-1(227 F g^-1).In addition,the capacitance retention rate was 100%after 10,000 charge/discharge cycles at 5A g^-1 under the two-electrode system.（3）MnO₂/graphene composite bamboo cellulose carbon aerogel was successfully synthesized by hydrothermal method.The results showed that the electrochemical properties of the composites were firstly improved and then decreased with increasing MnO₂ deposition amount.The microstructure and electrochemical properties are critical when 5m M KMnO₄ was added.At this time,the MnO₂ nanosheets are uniformly covered on the surface of the graphene composite bamboo cellulose carbon aerogel and the composite material had the largest specific capacitance because of the saturation state of the redox reaction of MnO₂.（4）An asymmetric supercapacitor was assembled by using MnO₂/graphene composite bamboo cellulose carbon aerogel as a positive electrode and the nitrogen doped bamboo cellulose carbon aerogel as a negative electrode.This asymmetric supercapacitor demonstrated a superior specific capacitance of 68.8 F g^-1 at 0.5 A g^-1 in an operating potential range of 0～1.3V.Moreover,it retained 94%of initial specific capacitance after 8000 cycles at 2 A g^-1,and revealed a high energy density of 16.2 Wh kg^-1at a power density of 163 W kg^-1.In general,a flexible carbon aerogel with good surface wettability,excellent conductivity and stability can be constructed by simply incorporating heteroatoms and graphene in situ.Using it as a matrix material to compound metal oxides can effectively improve the electrical conductivity and stability and solve the problem of uneven depositing.And the synergistic effect between the three can be achieved by adjusting the distribution ratio of each group.