Performance And Regulation Mechanism Of Cellulose Based Composite Flexible Electrodes

With the advancement of the"13th Five-Year Plan"of the green development concept,the scientific development and utilization of biomass resources have attracted widespread attention.Cellulose is an important part of biomass materials.The high-value development and application of cellulose resources are of great significance to the realization of sustainable development.In this thesis,cellulose-based materials are used as flexible substrates,and cellulose-based composite electrode materials are prepared by interface assembly and molecular control.The electrochemical properties and enhanced mechanism of the electrode materials were investigated and the microstructure and mechanism of the cellulosic matrix composites were optimized and adjusted.The applications of the composite materials in flexible supercapacitors and sensors were discussed.Aiming at the problem of poor conductivity of cellulose-based materials,paper pulp fibers are used as the substrate,graphene is used as the conductive medium,and a non-adhesive,flexible,self-supporting pulp fiber/graphene film electrode is designed and synthesized by constant temperature water bath and vacuum filtration method.The loose porous structure of the pulp fiber provides a channel for the ion transmission of the electrode,and graphene provides good mechanical flexibility.The area specific capacitance of the pulp fiber/graphene film electrode is 683 m F cm^-2.Furthermore,polyacrylamide（PAM）is used to modify the pulp fiber/graphene film electrode.Graphene oxide contains carboxyl and hydroxyl groups that can form a hydrogen bond structure with the amide group on the polyacrylamide molecular chain to improve the mechanical flexibility of the film electrode.After 500 bending and folding cycles,the capacitance retention rate is 87.65%.In order to increase the energy density of the film electrode,Mn O₂ nanoparticles are grown on the surface of the pulp fiber/graphene film electrode.The flexible film provides active sites for the electrode material and facilitates the deposition of Mn O₂.The obtained film electrode is assembled into a flexible supercapacitor with energy density of 61.01 m Wh cm^-2 and power density of 1249.78 m W cm^-2.The high-temperature carbonization method is further used to carbonize the pulp fiber to obtain a functional material with conductive properties—carbonized pulp fiber.The interconnected porous structure of the carbonized pulp board fiber provides a multi-dimensional transmission path for electrolyte diffusion and ion transfer,and improves the ion transmission rate.It is used as the substrate of flexible and self-supporting supercapacitor electrodes to explore the influence mechanism of natural organic matter-tannic acid on the electrochemical performance of cellulose-based graphene film electrode.Studies have found that tannic acid molecules contain a large number of benzene ring structures,which can interact with graphene oxide inπ-πconjugated interactions.The phenolic hydroxyl groups on the benzene ring can be converted into quinone groups,undergo redox reactions and provide pseudocapacitance.On this basis,the anode constant current electrodeposition method is used to deposit metal oxide（Mn O₂）and conductive polymer（PPy）on its surface,respectively.The assembled flexible asymmetric supercapacitor has an area specific capacitance of 1.383 F cm^-2,and its capacitance retention rate is 90.12%after 10,000charge and discharge cycles.Based on the advantages of carbonized cellulose materials with high conductivity,large specific surface area,and developed pore structure.The carbonized cotton pulp is used as the substrate material by the high-temperature carbonization method.Combined with the self-assembly performance of graphene,the highly porous structure of cellulose-based graphene hydrogels is prepared by the one-step hydrothermal method.The regulation mechanism of quinone organics on cellulose-based graphene hydrogel and the effect on electrochemical properties were explored.Studies have found that juglone molecules can provide redox active sites for graphene during the redox process.The hydrogel electrode prepared by the hydrothermal method has good rate performance,and the capacitance retention rate can reach 89.75%at higher current density.The conjugated carbonyl group of the anthraquinone molecule can form aπ-πconjugate with graphene,and regulate the pore structure and surface groups of the graphene hydrogel to form a stable three-dimensional porous network structure.The prepared hydrogel electrode has improved specific capacitance(490.2 F g^-1)and energy density(36.18 Wh kg^-1),and the capacitance retention rate is 92.15%after 1000 bending and folding cycles.After the cotton pulp fiber is carbonized,a large amount of oxygen-containing groups were removed from the cellulose and converts into a graphitic carbon structure,giving the carbonized cotton pulp fiber high conductivity and flexibility.The electrical conductivity of the carbonized cotton fiber is 12.21 S m^-1.It is used as conductive fillers and polydimethylsiloxane is used as a polymer matrix to prepare a cellulose-based pressure composite film with high flexibility and sensitivity.When the carbonized cotton pulp fiber content is 35%,the conductivity of the composite film is 0.43 S m^-1.Combined with its unique surface morphology,the composite film can be used to prepare piezoresistive sensors.The sensor has a continuous and stable response to load and unload.The maximum sensitivity is 10.8 k Pa^-1,and the durability exceeds 900 times under a stress of 10 k Pa^-1.And the sensor can detect the human movement changes,such as blinking,bending of fingers and elbow joints,and muscle movement of the vocal cords.The composite film has a mass specific capacitance of 89.3 F g^-1,which has potential for application in compressible supercapacitor electrodes.