Preparation And Electrochemical Performances Of Sawdust-based Porous Graphitic Carbon

Supercapacitors are widely used because of their advantages of large specific capacity and high specific power,and no pollution to the environment.Porous carbon materials,as commonly used electrode materials,have received great attention due to their well-developed pore structure and extensive source of raw materials.Using biomass as raw material to prepare porous carbon can not only save the cost of raw materials,but also alleviate the problem of environmental pollution caused by the incineration of waste biomass,and realize the high-value utilization of biomass into high-performance porous carbon materials with controllable structure and performance.However,structural defects such as too simple pore structure and a low degree of graphitization commonly exist in waste biomass carbon materials.It is necessary to activate and catalyze biomass to realize the performance modification of porous carbon materials and improve its electrochemical performance.At the same time,we study the effects of different activators and different metal catalysts on their electrochemical performance,which provides a theoretical basis for the development and utilization of electrode materials with excellent performance.The specific research contents are as follows:（1）Using waste biomass sawdust as raw material,KOH as an activator,bimetallic nickel and molybdenum as joint catalysts and templates,porous graphitic carbon was prepared at a low carbonization temperature of 750°C.The graphitization degree of porous carbon material PGC-Ni-Mo prepared by bimetallic Ni-Mo catalyst can reach 1.05,which is 3.0%,8.2%,and 9.4%higher than that of typical porous carbon materials prepared by single metal Ni,Mo,and typical porous carbon materials prepared without catalyst,respectively.Using PGC-Ni-Mo as the electrode material of the supercapacitor,its specific capacitance reaches 267 F g^-1.The rate capability of PGC-Ni-Mo reaches 77.2%at 10 A g^-1,which is 40.1%,4.0%,and34.7%higher than that of single metal Ni,Mo,and porous carbon materials prepared without catalyst,respectively.The specific capacitance of PGC-Ni-Mo remained94.8%after 10,000 cycles at 100 A g^-1.The energy density of the PGC-Ni-Mo//PGC-Ni-Mo symmetric supercapacitor is 19.8 Wh kg^-1at a power density of 452.9 W kg^-1in 1 M Na₂SO₄electrolyte.（2）In view of the shortcomings of the complex process of synthesizing porous graphitic carbon and the strong corrosiveness of the activator,a potent green disinfectant K₂Fe O₄was used as the activator and catalyst to convert the sawdust into high value-added porous graphitic carbon through one carbonization.The experimental results show that adjusting the mass ratio between sawdust and catalyst can effectively adjust the pore structure of the biomass carbon material,thereby optimizing the performance of supercapacitors.When the mass ratio of K₂Fe O₄to sawdust was 1:2,the specific surface area of the prepared porous graphitic carbon PGSC-2 was 1197.42 m²g^-1and the graphitization degree was 1.03.In the three-electrode system,the electrode PGSC-2 has a higher specific capacitance(327 F g^-1),and after 10,000 cycles,the capacitance retention rate of PGSC-2 is 99.7%with only slight attenuation.In the two-electrode system,the time constant of the as-assembled PGSC-2//PGSC-2 symmetric supercapacitor in 6 M KOH aqueous solution is 1.8 s,indicating that the electrode PGSC-2 possesses fast ion transport capability.The maximum energy density of PGSC-2//PGSC-2 in 1 M Na₂SO₄electrolyte is 25.6 Wh kg^-1.