Study On The Hierarchical Regulation Of The Pore Structure Of Bamboo Charcoal And Its Capacitance Properties

As a renewable raw material for charcoal,biomass is an essential component of the circular economy of the future.The efficient use of biomass resources is extremely important,but it also faces a number of challenges.Currently,the under-utilisation of biomass resources results in the generation of large amounts of solid waste.Therefore,it is important to prepare biomass waste resources into electrode materials with excellent supercapacitor properties and to realise their high value utilisation.In this thesis,bamboo shavings-based hierarchical porous carbon with excellent capacitive properties was prepared by hydrothermal carbonisation combined with chemical activation strategy using waste bamboo shavings raw materials.To solve the problem that the origin and formation mechanism of the pore structure in bamboo shavings-based hierarchical porous carbon are still unclear,the origin and pore formation mechanism of different size pores in bamboo shavings-based hierarchical porous carbon and its capacitance properties were investigated,and the relationship between the role of microstructure and capacitance properties was established.With the practical application as the target,to solve the problems of small specific surface area,low specific capacitance and low energy density of bamboo shavings-based hierarchical porous carbon,high performance and low cost double electric layer capacitor（EDLC）carbon electrode materials were prepared by regulating the microscopic pore structure and surface chemical properties of bamboo shavings-based hierarchical porous carbon,and the mechanism of the role of different size pores in the hierarchical porous structure in the EDLC process and the effect of surface modification（heteroatom doping）on the microstructure,surface chemical properties,electrochemical performance and charge storage mechanism of the materials were investigated.（1）Bamboo shavings-based hierarchical porous carbon（BPC）with excellent supercapacitor capacitance properties was prepared from waste bamboo shavings by carbonisation and CO₂-induced catalytic activation of small doses of K₂CO₃ using its unique natural vascular bundle macroporous structure.A simple and efficient method was used to successfully split the three components of bamboo shavings（cellulose,lignin and hemicellulose）.By investigating the changes in the microscopic pore structure of the three components of bamboo shavings during charring and activation,the origin of the different size pore structures in BPC and the formation mechanism of the hierarchical porous structure are elucidated.Bamboo shavings cellulose and hemicellulose mainly provide the microporous structure for BPC.Bamboo shavings lignin not only provides a large number of mesopores,but also an abundance of micropores.The macroporous structures in BPC are mainly derived from the better preservation of the original vascular structure in bamboo shavings,while the mesopores and micropores are formed during the charring and activation processes.In addition,the role of microstructure in relation to the capacitance properties is established by investigating the differences in electrochemical properties between bamboo shavings porous carbon and its porous carbon derived from different components.Compared to the porous carbon derived from other components,the bamboo lignin-derived porous carbon presents the best specific capacitance(273 F g^-1,0.5 A g^-1)and rate performance(82.6%capacity retention,20 A g^-1)due to the largest specific surface area(1985 m² g^-1)and highest micro-mesopore volume,revealing that the lignin plays a significant role in the excellent specific capacitance and rate performance of BPC.The excellent cycling stability（98.2%capacitance,15,000 cycles）of bamboo shavings cellulose derived porous carbon due to its excellent electrical conductivity and stable carbon skeleton structure indicates that cellulose is essential for the excellent cycling stability of BPC.The presence of bamboo hemicellulose also contributes to the specific capacitance,electrical conductivity and energy density of BPC to some extent.In combination with lignin,cellulose and hemicellulose,BPC has a well-developed hierarchical porous structure and excellent electrochemical properties.（2）A novel and efficient FeCl₃-catalyzed hydrothermal pretreatment combined with KOH activation strategy was used to prepare waste bamboo shavings into honeycomb hierarchical porous carbon electrode materials with ultra-large specific surface area and excellent supercapacitor performance by means of a microscopic pore structure modulation strategy to improve the capacitive properties of the materials.The specific surface area of the hierarchical porous carbon of bamboo shavings after low-temperature FeCl₃ hydrothermal pretreatment increases significantly(from 2164 m² g^-1 to 3688 m² g^-1)compared to that of the untreated FeCl₃ solution.The important effects of preparation conditions（different activation temperatures and carbon to base ratios）on the physicochemical structure and electrochemical properties of porous carbon electrode materials are further elucidated through a systematic study.Based on the unique microstructural properties,the prepared porous carbon electrode material exhibits excellent specific capacitance(378 F g^-1,0.5 A g^-1),good rate performance(capacity retention up to 71%,20 A g^-1)and high energy density(up to 10.3 Wh Kg^-1 at250 W kg^-1,more than twice that of the unmodified porous carbon)in KOH electrolyte,which effectively improves the competitiveness of porous carbon materials for EDLC applications.（3）A simple and efficient H₃PO₄-catalyzed hydrothermal pretreatment combined with KOH/melamine chemical activation was used to prepare waste bamboo shavings into petal-like hierarchical porous carbon electrode materials with a large specific surface area(3392 m² g^-1)and a nitrogen-oxygen co-doped interface by means of a heteroatom doping strategy to introduce pseudocapacitance to further improve the capacitance properties of the materials.The effects of surface modification（heteroatom doping）and optimal regulation of the hierarchical porous structure on improving the electrochemical properties of the carbon materials are systematically elucidated.Based on the excellent microscopic pore structure characteristics and surface chemistry,the modified carbon materials show good potential for practical applications in supercapacitors,with excellent capacitance properties in 6 M KOH electrolytes,including superior specific capacitance(501.6 F g^-1,0.5 A g^-1),excellent cycling stability(10,000 cycles at a current density of 5.0 A g^-1)after 10,000 cycles at a current density of 5.0 A g^-1)and the high energy density of 15.3 Wh kg^-1 at a power density of290 W kg^-1 achieved by the assembled symmetrical supercapacitor device.In addition,the charge storage mechanism of the modified porous carbon electrode material is dominated by surface-controlled processes,and the high surface-controlled ratio facilitates the structural stability of the material during cycling to achieve good cycling and rate performance.