Preparation And Mechanism Study Of Nanocellulose Based Supercapacitor Electrode

As the biodegradable nanomaterials,nanocellulose has high specific surface area,good hydrophilicity and excellent mechanical properties,which makes nanocellulose-based supercapacitor electrodes gradually become a research topic.However,nanocellulose is not conductive,so the application in electrode materials is still a challenge.In fact,nanocellulose has a high aspect ratio,the surface contains chemically modified hydroxyl functional groups,which can not only disperse conductive nanomaterials,but also self-assemble with conductive polymers by hydrogen bonds,which has attracted many researchers to focus on the nanocellulose composite electrode materials of their derivatives.At present,the application of nanocellulose in supercapacitor electrode has made great progress,but their electrochemical properties mainly resulted in the characteristics of the material itself like the pore structure and preparation method.Therefore,how to optimize the electrochemical performance of supercapacitor electrode from the electrode preparation mechanism,pore structure regulation and preparation method is still a difficulty for developing high performance supercapacitor electrode.Hence,this thesis using nanocellulose as the main raw material,and the supercapacitor electrodes with good electrochemical properties are prepared by using its dispersion,hydrophilic,hydroxyl functional group etal.to form hydrogen bonding,physical crosslinking and in situ polymerization reaction.The specific research contents are as follows:（1）In order to explore the influence of nanocellulose on the microstructure and electrochemical properties of composite aerogel electrode,the TOCNFs were used as raw material in this chapter.First,using TOCNFs to disperse the MWCNT,then through Ca²⁺crosslinking SA to form a conductive network.Finally,the PPy successfully loading composite aerogel in the conductive network by hydrogen bonds self-assembly.The pore structure and electrochemical properties of the composite aerogel electrodes were regulated by the ratio of TOCNFs and SA.The results show that the preparation of composite aerogel is realized by physical cross-linking and hydrogen bond self-assembly,and its pore structure and electrochemical properties are regulated by TOCNFs content.The weak redox peak appears on the CV curves,indicating the coexistence of electric bilayer and pseudocapacitive behavior of the as prepared composite aerogel electrode during charge storage.When the mass ratio of nanocellulose to sodium alginate was 1:3,the specific surface area was 11.99 m²·g^-1,the content of PPy was 35.29 wt%,and the area capacitance was 780.5 mF·cm^-2.The capacitor remains 89.31%after 3000 cycles.（2）The electrochemical performance of the composite aerogel is improved by loading the high theoretical specific capacitance MnO₂.Using Fe³⁺as the cross-linkinger to establish a stable network structure with nanocellulose and sodium alginate by forming complex bonds,while using the oxidation of Fe³⁺to synthesize PPy,and tightly bond to the conductive network through hydrogen bonding.Compared with the previously research,the area specific capacitance is up to 3336.5 mF·cm^-2,with the energy density and power density of 166.83μWh·cm^-2 and 1575.91μW·cm^-2,respectively.Furthermore,the composite aerogel has a conductivity of 50 mS·cm^-1.At the high current density of 20m A·cm^-2,the supercapacitor was retained 87.99%after 1000 charge-discharge cycles.（3）Although regulating the electrode electrochemical properties,unreasonable cross-linking and self-assembly behavior can cause negative effects like low specific surface area and uneven pore size distribution.Based on this,TOCNFs compounded with MWCNT,and composite aerogel electrodes were prepared by Fe³⁺as a crosslinker and oxidant after freeze-drying.Through ion diffusion,Fe³⁺is prompted to diffuse slowly along the longitudinal direction,forming complex bonds and initiating the in-situ polymerization reaction of aniline monomer during the diffusion process.The effect mechanism of different TOCNFs content on the structure and electrochemical properties of composite aerogel were investigated.As a result,the prepared composite aerogel has uniformly distributed conductive network and mesoporous structure.The content of TOCNFs not only affects the specific surface area and average pore size of the composite aerogel,but also affects the loading of the PANI.The electrochemical test shows that the composite aerogel has highly reversible faradaic pseudocapacitance behavior.The conductivity is 27.3 mS·cm^-1 and the area specific capaciance is 2176.30 mF·cm^-2.At the current density of 10 mA·cm^-2,the capacitance remains of the compoiste aerogel electrode is 64%after 1050 cycles.