The Preparation Of Biomass Carbon-based Composites For High Efficient Supercapacitors

Nowadays,the conversion and storage of clean energy have gradually aroused people's attention due to the increasing pollution and energy crisis.Especially the growing demand for the new energy vehicles and mobile intelligent devices promotes the developing of the new type energy storage device with high energy density and long life.Among the existing energy storage systems,supercapacitors have aroused a great deal of concern due to their excellent power density,fast charging-discharging,long lifespan and environmental friendliness.However,the intrinsically low energy density and poor rate performance severely hinders its wide application.As we all know,the performance of supercapacitors mainly depends on the properties of electrode materials.The structure and internal resistance of materials have a great influence on the performance of the capacitors.Biomass-derived porous carbon materials and their metal composites exhibit tremendous potential in this field due to low cost,easy processing,good electrical conductivity and excellent performance.Biomass is a sustainable carbon carrier in the nature.Among them,poplar catkin is the micro-level hollow fiber derived from the broken seed of poplar,which are harmful to human health and can cause inconvenience to people's travel.In addition,glucose is a kind of monosaccharide widely distributed in the nature,and it shows a broad prospect in the field of supercapacitors as a precursor to prepare porous carbon materials.Therefore,in this paper,a series of electrode materials were designed with poplar catkin-derived carbon and glucose-derived carbons,and then different types of capacitor devices were assembled based on these materials.Furthermore,their electrochemical properties were tested to comprehensively evaluate their potential in supercapacitors.The main contents and results are as follows:?1?Hollow carbon microtubes were obtained by pyrolysis of natural poplar fibers at high temperature in Ar atmosphere,and then carbon microtubes were treated with probe ultrasonic treatment to obtain microsheets?PC?.Finally,the surface of PC was modified by self-polymerization of dopamine to obtain PD-PC.The characterization results show that PD-PC has a two-dimensional lamellar structure,surface functional groups have a notable increase,and the hydrophilicity is greatly improved.The electrochemical performance of both shows that PD-PC electrode materials possess higher specific capacitance?206.3 F/g,1A/g?,excellent rate performance?78%capacitance retention at 10 A/g?and lower charge transfer resistance.The reason can be attributed to the fact that good hydrophilicity promotes the diffusion of electrolyte on the electrode surface and improves the transmission of electrons.?2?A simple hydrothermal method combined with low temperature annealing was used to prepare 3D micro-nano structure materials?NiCo₂O₄ NSs@PD-PC?with PD-PC as the carbon matrix.The characterization results show that NiCo₂O₄NSs@PD-PC has a 3D micro-nano composite structure with distinct boundaries and interconnected space compared with pure NiCo₂O₄ and NiCo₂O₄ NSs@PC.In the three-electrode system,this composite material has a specific capacity of 922.9 C/g at1A/g,57.3%capacity retention at 20 A/g,91.4%after 5000 cycles,and low internal resistance.In the two-electrode system,the asymmetric devices assembled with NiCo₂O₄ NSs@PD-PC as the positive electrode and PD-PC as the negative electrode also show high energy density and power density,good cycling stability and broad practical application.The reason can be attributed that the polydopamine layer can act as the"bridging layer"to promote the coupling of two materials,which thus reducing the aggregation of NiCo₂O₄.?3?The polymer organic frameworks?POFs?were obtained by a simple hydrothermal reaction combined with freeze-drying using glucose as the carbon source and melamine as the nitrogen source.And the N-doped glucose-based multi-porous carbon microspheres?NCM?were obtained by a pyrolysis at high temperature with POFs as the self-template.The results show that NCM products possess hierarchical porous structure with center-radial pore channels,large surface area?603.9 m²/g?and high nitrogen doping?11.26 at.%?.In the three-electrode system,the NCM sample shows a specific capacitance of 280.8 F/g at 0.5 A/g,the capacitance retention of 62.5%at 20 A/g,and the capacitance retention of 92.2%after5000 cycles.In the two-electrode system,the assembled symmetric devices also show high energy density?21.8 Wh/kg?,power density?10000.4 W/kg?,and broad application prospects.These excellent electrochemical properties can be attributed to the synergistic effect of hierarchical pores structure and high-level nitrogen doping.In conclusion,two kinds of biomass carbon-based materials were prepared by different methods using poplar catkin and glucose as precursor in this study,and the electrochemical performances of NiCo₂O₄ NSs@PD-PC and nitrogen-doping carbon microspheres were investigated.Our research provides a new idea for the application of biomass carbon-based materials.