The Preparation Of Low-Dimensional Carbon Electrode Materials Derived From Biomass And Their Supercapacitive Behavior

In the face of increasingly severe environmental pollution and climate change issues,developing efficient energy storage systems to store and utilize renewable energy is critical to achieving sustainable societal development.Supercapacitors have advantages such as fast charging and discharging rates,high power density and long cycle life,being expected to become essential components of the next-generation energy storage systems.Developing high-performance electrode materials is key to improve the performance of supercapacitors.Low-dimensional structural carbon materials such as graphene and carbon nanotubes are widely studied due to their large specific surface area,high conductivity and good stability.However,high raw material costs and complex preparation processes hinder their large-scale application.Therefore,using widely available,low-cost,environmentally friendly and structurally diverse biomass resources to prepare low-dimensional carbon materials has become a new research direction.However,biomass-derived carbon materials generally have defects such as narrow pore size distribution,simple pore structure,low surface activity and poor conductivity,which greatly limit their supercapacitive performance.Given the above problems,this paper uses biomass as the precursor and employs various methods such as carbonization,activation,electrospinning and self-assembly to prepare a series of low-dimensional electrode materials,including carbon nanospheres,carbon fibers,layered carbon materials,and Ti3C2Tx nanosheets/carbon nanospheres composite.Through the construction of multi-level structures,the specific surface area,pore structure,chemical composition,and conductivity of biomass-derived low-dimensional carbon materials were optimized to improve their supercapacitive performance.The materials’ composition,structure,and electrochemical properties were investigated and analyzed using various characterization and testing methods,and the impact mechanisms of materials’ composition and structure on their electrochemical performance were also intensely studied.The paper contains the following five parts:1.Preparation of cuttlefish ink-derived carbon nanospheres and thier supercapacitive behaviorFe-decorated N/S-codoped hierarchical porous carbon nanospheres were prepared by Fe2(SO4)3-assisted hydrothermal carbonization and heat treatment with cuttlefish ink as the precursor.The effects of Fe2(SO4)3 dosage on the graphitization degree,heteroatom doping,pore structure and supercapacitive performance of carbon nanospheres were investigated.The results show that Fe2(SO4)3 can play a multifunctional role.Firstly,it can improve the material graphitization degree as a graphitization catalyst.Secondly,it can introduce S and Fe elements into the material as a doping agent.Lastly,it can change the pore structure framework of the material as a morphology-regulating agent.With the increase of Fe2(SO4)3 dosage,the graphitization degree and the content of S and Fe elements in carbon nanospheres gradually enlarge.However,excessive Fe2(SO4)3 can cause over-catalytic graphitization,thereby destroying the material’s spherical structure and pores,and leading to the decrease in specific surface area and pore volume.The carbon nanospheres exhibit optimal supercapacitive performance acquired under the condition of a 10:1 mass ratio between precursor and Fe2(SO4)3,including high specific capacitance(312 F·g-1 at a current density of 0.5 A·g-1),large rate capability(only a 19.1%decrease in specific capacitance with rising current density from 0.5 to 10.0 A·g-1),and good cycling stability(with a capacitance retention of 94.3%after 5,000 cycles),which is attributed to the moderate graphitization degree,hierarchical porous structure and rich heteroatom content of material.The symmetric supercapacitor assembled with this carbon nanosphere material as electrodes exhibits an energy density of 9.7 Wh·kg-1 at a power density of 0.25 kW·kg-1,and a capacitance retention rate of 91.3%after 10,000 cycles.2.Preparation of cuttlefish ink-derived carbon fibers and thier supercapacitive behaviorNecklace-like N-doped porous carbon fibers were prepared by electrospinning and carbonization method using cuttlefish ink-derived carbon nanospheres as the primary structural units,polyacrylonitrile(PAN)-based pyrolytic carbon as the framework,and polymethyl methacrylate(PMMA)as the sacrificial template.The optimization mechanisms of cuttlefish ink-derived carbon nanospheres and PMMA on pore structure and supercapacitive performance of the carbon fibers were investigated.The results show that the spherical porous structure of cuttlefish ink particles can significantly expand the specific surface area and pore volume of the carbon fibers,thereby increasing the specific capacitance of the material.PMMA can create multiple parallel hollow channels inside the carbon fibers,which helps to accelerate ion diffusion.As a result,the necklace-like carbon fibers reveal ideal capacity(the specific capacitance reaches 365 F·g-1 under a current density of 0.5 A·g-1),good rate performance(the specific capacitance decreases by only 20.7%when the current density increases from 0.5 to 10.0 A·g-1),and high cyclic stability(the capacitance retention rate is 98.9%after 5,000 cycles).Furthermore,the carbon fibers have good mechanical flexibility.The assembled flexible solid-state supercapacitor based on the carbon fibers shows an energy density of 14.1 Wh·kg-1 at a power density of 0.40 kW·kg-1,and a capacitance retention rate of 97.8%after 5,000 cycles.3.Preparation of hypha-derived carbon fibers and their supercapacitive behaviorBy combining biological self-assembly,artificial self-assembly and surface modification methods,the N-doped porous carbon fibers with small tubes covering large tubes were prepared by modifying hollow carbon nanotubes on the hollow carbon fibers derived from hypha and grafting amino functional groups onto them.The effect of multilevel hollow structure and amino functional groups on the ion transfer characteristics,conductivity,hydrophilicity and supercapacitive performance of the carbon fiber was studied.The results show that the multi-level hollow structure of the carbon fiber can enhance the ion adsorption capacity while providing rapid ion transfer paths,whereas surface amino functional groups can increase the specific capacitance and hydrophilicity of the material.Additionally,the multi-level hollow structure and amino functional groups enhance the material’s conductivity.Compared to the unmodified raw carbon fibers derived from hypha,this carbon fiber material offers a higher specific capacitance(289 F·g-1 at a current density of 0.5 A·g-1).Furthermore,the carbon fibers exhibit good mechanical flexibility.The flexible solid-state supercapacitor assembled with the carbon fiber electrode material achieves an energy density of 12.2 Wh·kg-1 at a power density of 0.21 kW·kg-1.Even after 10,000 cycles,its capacitance can still maintain 86.9%of the initial value.4.Preparation of porcine bladder-derived layered carbon material and its supercapacitive behaviorN-doped porous carbon material with a layered structure was prepared using porcine bladders as the precursor through carbonization and activation methods.The effect of the dosage of KOH activator on the specific surface area,layered structure,pore size distribution and nitrogen doping level of the carbon material was investigated.The results show that KOH could effectively etch the carbon material and create rich pores.As the dosage of KOH increases,the carbon material’s specific surface area and pore volume become larger.However,excess KOH could cause the destruction of layered structure and the collapse of pore structure,and significantly reduce the nitrogen doping amount.The carbon material prepared with a mass ratio of activator to pre-carbonized material of 2:1 demonstrates the optimal supercapacitive performance,including high specific capacitance(323 F·g-1 at a current density of 0.5 A·g-1),good rate capability(79%capacitance retention with increasing current density from 0.5 to 10.0 A·g-1),and long cycling life(96.4%capacitance retention after 5,000 cycles).Such good performance is mainly due to the carbon material’s sizeable specific surface area(1881.7 m2·g-1),hierarchical porous layered structure,moderate graphitization degree and high nitrogen content(5.4%).The symmetric supercapacitor assembled with this layered carbon material as electrodes shows an energy density of 10.9 Wh·kg-1 at a power density of 0.15 kW·kg-1.Additionally,this supercapacitor affords a capacitance retention rate of 95.6%after 5,000 cycles.5.Preparation of Ti3C2Tx nanosheets/cuttlefish ink-derived carbon nanospheres composite and its supercapacitive behaviorTi3C2Tx nanosheets/cuttlefish ink-derived carbon nanospheres composite with heterostructure was prepared through the electrostatic self-assembly.The optimization mechanism of the heterostructure for the ion transport kinetics and supercapacitive performance of the composite material was studied.The results show that the cuttlefish inkderived carbon nanospheres,which were inserted into the interlayer of Ti3C2Tx twodimensional transition metal carbide(MXene),can effectively enlarge the interlayer spacing of MXene and prevent the nanosheets from tight stacking.On the one hand,this heterostructure promotes the expansion of specific surface area and the exposure of active sites,which helps to improve the material’s charge storage capacity and accelerate ion/electron transport.On the other hand,it alleviates the volume change effect of the material during the charge-discharge process,which enhances the material’s cycle stability.Compared with the pure MXene,the composite material accommodates significantly improved specific capacitance(264 F·g-1 at the current density of 0.5 A·g-1),rate performance(23.1%capacitance decrease with the increasing current density from 0.5 to 10.0 A·g-1),and cyclic stability(93.4%capacitance retention after 5,000 cycles).The assembled symmetric supercapacitor based on this composite material shows an energy density of 5.1 Wh·kg-1 at a power density of 0.18 kW·kg-1 and a capacitance retention of 91.7%after 5,000 cycles.