Morphology Modulation And Electrochemical Properties Of Bacterial Cellulose-Derived Carbon/MnO₂ Composites

The development of low-cost,low-carbon,and environmentally friendly green energy storage devices is an essential part of meeting sustainable development goals.Electrochemical energy storage（e.g.,fuel cells,secondary batteries,etc.）can effectively solve the problems of poor regional distribution of resources and their timeliness.Among them,supercapacitors are emerging in the field of portable electronic devices,new energy vehicles and aerospace because of their excellent cycle stability,high energy density and high power density.As the key part of supercapacitors that affects the energy storage effect,the research on electrode materials is increasing.In recent years,manganese dioxide（MnO₂）has received much attention because of its high theoretical capacitance,low price and environmental friendliness.However,the poor electrical conductivity and the ease of agglomeration in the preparation process have led to the unsatisfactory electrochemical performance,which has greatly restricted its application.To solve the above problems,in this paper,bacterial cellulose-derived carbon materials with good electrical conductivity are used to prepare bacterial cellulose-derived carbon/MnO₂ nanocomposites by optimizing the preparation process and regulating the microscopic morphology by combining MnO₂,which possesses high theoretical specific capacitance,as follows:1.To address the shortcomings of MnO₂,which is prone to agglomeration and poor electrical conductivity,a three-dimensional interconnected honeycomb-like bacterial cellulose-derived carbon/MnO₂ composite（3DIHBC/MnO₂）was prepared by a one-step carbonization and hydrothermal method using green and natural bacterial cellulose as the substrate.The purified carbonization of bacterial cellulose produced a three-dimensional honeycomb-like carbon material with a relatively excellent specific surface area(241.9 m²g^-1),which also provided a good substrate for further loading of nano-flower-like MnO₂.The poor electrical conductivity of MnO₂,while the stable pseudocapacitance of MnO₂ enhances the energy storage effect of the carbon material.The composite material can achieve a specific capacitance of 170 Fg^-1at 1 A g^-1,and the power density of the assembled symmetrical devices can reach up to 10500 W kg^-1with 3DIHBC/MnO₂ as positive and negative electrodes under a voltage window of 2.0 V.This work integrates environmental and energy issues,and provides a feasible strategy for the development of environmentally friendly electrode materials preparation.2.After compounding MnO₂ with bacterial cellulose as the substrate,the disadvantage that MnO₂ is easy to agglomerate can be greatly improved.However,the improvement of cycling performance and specific capacitance will largely depend on the microscopic morphology of the electrode material,therefore,after optimizing the purification carbonization step,different morphologies of the derived carbon were prepared in this part,and the reaction time was strictly regulated in the subsequent hydrothermal experiments to study the effect of hydrothermal time on the morphology and electrochemical properties of MnO₂-based composites.Bacterial cellulose carbon substrates with fibrous and three-dimensional pore structures were prepared by regulating the carbonization temperature rise rate,and the optimal carbon material was selected for subsequent experiments by comparing the performance tests,and the MnO₂-based composites were prepared according to different hydrothermal times by regulating the experimental conditions,and the best performance was found at 6 h of hydrothermal time after performance tests and characterization.The composite CBC-5@MnO₂-6h achieved a specific capacitance of 190 Fg^-1at a current density of 1 Ag-1 and a high specific capacity of 211 Fg^-1at 0.5 Ag^-1.The CBC-5@MnO₂-6h electrode maintained a capacity of 96.6%after 8000 long cycles.Asymmetric devices assembled using CBC-5 and CBC-5@MnO₂-6h have also been shown 11111.1W kg^-1high power density,the hybrid supercapacitor also only lost 9.7%after 5000 cycles,showing good capacitance characteristics.3.Although flower-like and nanospheric MnO₂ can be synthesized by a convenient hydrothermal method,the conventional hydrothermal method also has some unavoidable drawbacks.It was found that the assisted liquid-phase plasma electrolysis method can achieve rapid deposition of nanoparticles on carbon substrates.In this part,bacterial cellulose carbon nanofiber/MnO₂composites were prepared by the assisted liquid-phase plasma electrolysis method,and the rapid deposition of ultra-fine nanoscale MnO₂（10～20nm）on bacterial cellulose carbon nanofibers was achieved.The assembled capacitor devices also have excellent electrochemical performance with a capacitance loss rate of only 6.2%for the BCNF//BCNF/MnO₂ devices even after 5000 long cycles.This convenient method of synthesizing nanocomposites in a very short period of time has a great potential for industrial production.Thus,these properties of assisted liquid-phase plasma electrolysis open up new avenues for the synthesis of composite materials.