Fabrication Of Composite Materials Based On Carbonized Bacterial Cellulose And Their Application In Area Of Electrochemical Energy Storage

Entering into the new century,although fossil fuel has deeply promoted the rapid development of human society,the exploitation process brings about serious ecology and environment problems.Besides,fossil fuel has a limited storage and is draining off day after day.Therefore,it is a significant matter to explore new energy system with low-carbon style for achieving the sustainable development of society and economy.Electrochemical energy,as a clean energy form,has recently attracted extensive attention of researchers.Hybrid structural electrodes based on carbon nanomaterials are the key components in all electrochemical energy storage system.Carbon materials usually act as the supports for active substances in the design of electrodes owing to their good conductivity,high electrochemical stability,and abundant micro-nanostructures.Carbonized bacterial cellulose(CBC)is a typical biomass carbonaceous material with three-dimensional structure.CBC presents the self-standing and flexible features in macroscopic view and macroporous network derived from interconnected nanofibers in microscopic view.In this dissertation,the physicochemical properties of CBC are systematically studied first,and then several new energy systems based on CBC are reported.The electrochemical properties are carefully studied when CBC acts as electron conductive matrix,and the structure-activity relationship between electrochemical behaviors and electrode microstructure is elaborately explained.Besides,several new methods for preparing electrode composites have been proposed,which are suitable to this biomass carbonaceous material and its precursor.The main contributions of this dissertation are described as follows:1.Study on physicochemical properties of CBC along with carbonization temperature and the application of CBC in methanol electro-oxidation processIt makes a relatively comprehensive description and characterization towards to CBC according to its preparation procedure and its macro/micro-structure.Mercury intrusion test,as well as observation of electron microscope suggests that CBC possesses macroporous structure derived from interconnected nanofibers.XRD and Raman analysis indicate that despite the amorphous nature of CBC,it also contains ordered graphite structure.This graphite microcrystal can be directly observed by using of HRTEM,and its changes along with carbonization temperature are also presented.The evolution of graphite phase in CBC during carbonization is once more supported by the results of electrical conductivity tests with the help of percolation theory,which is a macroscopic proof from electrical property.CBC acts as conductive support for metal Pt,and the prepared composite is used for methanol electrocatalytic reaction.The remained oxygen groups on CBC surface serve as nucleation sites,and the large specific surface area is benefit for obtaining ultrafine metal particles.Metal-loading research model is utilized for preliminarily exploring the potential application value of CBC in energy storage electrochemistry.2.Pyrrole in situ coating reaction based on bacterial cellulose(BC)hydrogel system and the application of the carbonized materials in oxygen reduction catalysisN containing precursor with enwrapped structure is obtained through an in situ reaction,in which pyrrole serves as N source and BC nanofibers act as template.A new hydrothermal method based on BC hydrogel system is presented from this preparation process.After carbonization of the prepared composite precursor,oxygen reduction reaction(ORR)catalytic performance is investigated when the coating quantity of N-doped carbon is considered as a function.XPS is utilized to study the variation and transformation of N content and N configuration in composite materials along with carbonization temperature.Electrochemical tests demonstrate that both N content and N configuration have a remarkable effect on ORR catalytic performance.When compared with commercial Pt/C catalyst,the prepared N-doped carbon composite though presents worse ORR catalytic activity,it exhibits much better methanol tolerance and catalytic stability.3.Amorphous Fe2O3 coated on CBC nanofibers as a flexible anode for high-performance Li-ion batteries(LIBs)A flexible anode for LIBs is prepared by coating Fe2O3 nanoshells on the surface of CBC nanofibers.XRD and N2 adsorption/desorption measurements demonstrate that the coated Fe2O3 active materials possess both amorphous and nanoporous features.Electron microscope observations indicate that the macroporous network derived from interconnected nano fibers is still preserved after coating on Fe2O3.The superior structure could on one hand promote the transportation of electrons/ions,and on the other hand alleviate volume changes of Fe2O3 during cycling.Amorphous iron oxide electrode based on CBC provides larger capacity when compared with its crystalline counterpart.The special nanoporous structure of amorphous Fe2O3 could provide large electrochemical active surface,which could facilitate the interfacial and capacitive-like lithium storage of active materials and ultimately leads to large capacity.The relative stable cycling performance could be ascribed to“flexible”structure of amorphous Fe2O3.4.Flexible cathode and multifunctional interlayer based on CBC for high-performance lithium-sulfur(Li-S)batteriesFlexible S/CBC composites are prepared by using solution-impregnation method with CBC as conductive skeleton.The macroporous structure of CBC is benefit for high S loading,and the remaining pore volume after loading could facilitate Li+ conductivity and mitigate volume variation of S.Multifunctional CBC interlayer is also fabricated,which could notably improve electrolyte infiltration into S/CBC cathode.In addition,the CBC interlayer could directly reduce the polysulfides of those shuttling back to cathode and accommodate deposition of S species during charging process,which relieves the excessive accumulation of S species on surface of cathode.The active materials trapped by CBC interlayer could be reutilized in the next cycle.This work presents a novel perspective for polysulfides control with a strategy of“guiding”,which is a new method for solving“shuttle”problem from dynamic aspect.5.CBC based Fe3O4 composites fabricated by in situ hydrolysis and direct carbonization for supercapacitor anodeThe precursor of active materials is loaded through in situ hydrolysis of FeCl3 at a condition approaching room temperature,in which BC hydrogel acts as reaction system.The large specific surface area and abundant hydroxyl groups provide sufficient space and plenty of nucleation sites for loading,respectively.CBC based Fe3O4 composites are obtained by direct carbonization.The observation of electron microscope demonstrates that Fe3O4 nanoparticles are evenly loaded on the surface of CBC carbon fibers with fine dimension and narrow size distribution.Capacitance performance suggests that the prepared composites exhibit good rate capability and stable cycling properties,as well as high capacitance compared with pure CBC.This work is aimed to present a new method for preparing high-performance composite electrode,which has the characteristics of cost saving,environment friendly,and procedure convenient.