Study On Preparation And Electrochemical Performance Of Biochar-based Materials

At present,supercapacitors have received extensive attention because of their own advantages,and have been successfully applied in many fields.For example,it acts as a backup power source for electronic products,and is used in electric vehicles and hybrid vehicles,solar and wind power generation devices,military aerospace and other fields.The electrode material in supercapacitors is the most important part,which directly affects the performance of supercapacitors.Carbon material is one of the earliest and most mature electrode materials used in research.Graphene,carbon nanotubes,activated carbon,etc.are representative of carbon materials.However,due to the high production cost of graphene and carbon nanotubes,the low specific surface area of the materials and other shortcomings limit their development as electrode materials.Biomass has become an important source of carbon materials due to its wide source,low cost and renewable advantages.Biochar is produced by pyrolysis of biomass under anoxic conditions.However,Biochar has two problems in the actual application of supercapacitor electrode materials:first,Biochar pores are not developed and the specific capacitance is not high,usually the specific capacitance is about 165 F/g^[1];In aqueous electrolytes,the Biochar surface is hydrophobic,which results in a very limited effective specific surface area of the biomass carbon material.In response to the above two problems,first,the transition metal compound has ultra-high pseudo-capacitance,and the overall specific capacitance of the material is improved by doping the transition metal.Second,heteroatom doping can significantly improve wettability and improve the electrochemical performance of carbon materials.The electrode materials prepared by adopting the above method have different degrees of improvement in specific capacitance and excellent electrochemical performance.This will greatly improve the application potential of biomass carbon materials in supercapacitor electrode materials.Environmentally friendly and safe disposal of waste biomass will greatly reduce its impact on the environment and thus have a positive impact on environmental protection.In this paper,we mainly study lotus leaf biomass,and prepare bio-carbon materials by high-temperature carbonization,hydrothermal carbonization,KOH activation and other methods,and finally obtain carbon materials with high specific surface area and high specific capacitance.The main contents are as follows:?1?The transition metals selected in this thesis are zinc and iron.Pyrolysis doping and KOH activation are used to prepare porous carbon materials.KOH activation causes the material to generate a large number of mesopores,with an ultra-high specific surface area.Four kinds of activated carbon materials?KLC?,zinc-doped carbon materials?Zn-KLC?,iron-doped carbon materials?Fe-KLC?,and zinc-iron-doped carbon materials?Zn-Fe-KLC?were prepared in this experiment Electrode materials,of which the best performance is Zn-KLC electrode materials.When Zn-KLC is used as the electrode material,it shows excellent performance at a scan rate of 1 m V/s in a three-electrode system with a specific capacitance of 361 F/g.In addition,the symmetric supercapacitor assembled from two identical Zn-KLC electrodes has a longer cycle life after 5000 cycles in a two-electrode system,and the specific capacitance retention rate is 86.5%.?2?In aqueous electrolytes,due to the hydrophobic nature of the Biochar surface,this will result in a very limited effective specific surface area of Biochar.Hetero atom doping can significantly improve the wettability and improve the electrochemical performance of carbon materials.This experiment explored the effect of boron and sulfur doping on the performance of supercapacitors.Three electrode materials,boron-doped electrode material?BKLC?,sulfur-doped electrode material?SKLC?,and boron-sulfur-doped electrode material?BSKLC?were prepared in the experiment.The research results show that:BKLC material has the highest specific capacitance in the three-electrode system.At a scanning speed of 1 m V/s,it shows a specific capacitance of471 F/g.In addition,a symmetric supercapacitor assembled from two identical BKLC electrodes has a longer cycle life after 5000 cycles in a two-electrode system,and the specific capacitance retention rate is 90.3%.?3?Nitrogen has an effect on improving the wettability and conductivity of the material.Phosphorus can improve the charge storage and electron transport ability,improve the surface activity of the carbon material,and contribute to the electrochemical stability of the super capacitor.In this experiment,the effects of organic nitrogen phosphorus and inorganic nitrogen phosphorus on the electrochemical performance of supercapacitors were studied.The organic phosphorus doped carbon material?O-PKLC?,organic nitrogen doped carbon material?O-NKLC?,inorganic phosphorus doped Four kinds of electrode materials:hybrid carbon material?I-PKLC?and inorganic nitrogen-doped carbon material?I-NKLC?.The results show that the specific capacitance of the O-PKLC material is the highest in the three-electrode system.At a scanning speed of 5 m V/s,the specific capacitance is 400 F/g.After 5000 cycles,the cycle stability is95.4%This means that the material has huge energy storage potential.