Research On Resource Reuse Of MF Resin And Tobacco Waste In Supercapacitors

For the treatment of the large amount of waste of industrial resin and agricultural straw,traditional methods（such as incineration,landfill,etc.）are easy to cause serious environmental pollution problems,as well as the resource waste.In this paper,the waste of（melamine-formaldehyde resin（MF）,tobacco stalk and tobacco stalk core）are proposed to be carbon precursors,which can be converted into useful carbon materials through carbonization and activation process.The resulted carbon materials were used as electrode materials in supercapacitors.The effects of carbonation temperature,carbonization mode,the type and amount of activator on the structure and electrochemical properties of the carbonized products were systematically studied.The main contents are as follows:（1）To treat MF resin waste for fabrication of carbon products with high value.MF resin-derived carbon was successfully prepared by direct pyrolysis of MF resin waste,and we explored the influence of carbonization temperature（650 ^℃,750 ^℃ and 850 ^℃）on the electrochemical performance of MF resin-derived carbon.The results showed that the MF resin-derived carbon pyrolyzed at 750 ^℃ had the highest specific capacitance,however,its surface lacked of pores and its conductivity was poor.In order to increase the specific surface area of MF resin-derived carbon,activators were mixed with the MF resin waste.The effects of the activator type（nano-Ca CO₃,Mg CO₃ and Zn Cl₂）on the physical chemical structure and electrochemical properties of MF resin-derived carbon were explored.The results showed that nano-Ca CO₃ could be the best template for the preparation of the porous MF resin-derived carbon,and the corresponding product had a structure with rich pores and high specific surface area(920.3 m²·g^-1).At a current density of 0.5A·g^-1,its specific capacitance reached 295.3 F·g^-1.To increase the conductivity of MF resin-derived carbon,hot pressing and in-situ carbonization techniques were used to incorporate highly conductive CNTs into the carbon framework of MF resin,which was successfully used to prepare a carbon/carbon composite with dual conductive channels.The effects of the CNT ratios on the conductivity and electrochemical properties of MF resin-derived carbon materials were explored.When the addition amount of MF and CNT was 10:0.7,the conductivity of the carbon product was increased by 11.5-fold and its specific capacitance was as high as 319.6 F·g^-1(0.5 A·g^-1).The energy density of its symmetrical supercapacitor reached 9.5 Wh·kg^-1 at a power density of 400W·kg^-1,which made it able to drive LED lamps,confirming that carbon derived from MF resin waste had a wide application prospect in the field of energy storage.（2）To effectively utilize tobacco stalk waste.Waste tobacco stalk was used as carbon source in this part of work.As tobacco stalk itself had only a few heteroatoms in its macromolecules and a low specific surface area,which resultd in the low specific capacitance of its carbon products,new treatment techniques were thus adopted.Tobacco stalk was pretreated by high temperature and high-pressure hydrothermal method to attach oxygen-containing groups onto the product;KOH was further utilized to adjust its surface chemical composition and pore structure to prepare oxygen-doped activated carbon.The effect of the mass ratio of carbon obtained after the hydrothermal pretreatment to KOH on the physical and chemical properties of the final carbon products was also explored.When the alkali-carbon ratio was 1:1（TC-1）,the specific surface area of TC-1 was as high as 1875.5 m²·g^-1,and its oxygen element content was 8.31 at%.The doping of oxygen not only increased the wettability of the material and the charge transfer rate,but also contributed certain pseudocapacitance,which took a synergistic effect with the double-layer capacitance.Three-electrode tests showed that the specific capacitance of TC-1 was as high as356.4 F·g^-1(0.5 A·g^-1).The symmetric supercapacitor assembled with TC-1dispalyed an energy density of 10.4 Wh·kg^-1at a power density output of 300 W·kg^-1.After 5000 cycles of charging and discharging,the capacitance still remained 92.8%,showing its excellent cyclic stability.（3）To make full use of tobacco waste.Activated carbon with graded pores was successfully prepared from tobacco stalk core by low-temperature pre-carbonization and high-temperature activation.In the fabrication process,its inherent KCl salt particles acted as the self-templates,and they were further combined with different proportions of KOH to regulate the porosity of the carbon derived from the tobacco stalk core.The results showed that at the optimal KOH ratio(m _KOH:m_{precarbonization product}=3:1),the prepared TCAC-3 had an ultra-high specific surface area and abundant micropores and mesopores.It exhibited a specific capacitance of up to 440.6 F·g^-1 at a current density of 0.5 A·g^-1,and its capacitance remained to be 72.1%when the current density was increased by 20 times.The assembled TCAC-3//TCAC-3 symmetrical supercapacitor displayed an energy density of 12.3 Wh·kg^-1(300 W·kg^-1),indicating that tobacco stalk core derived carbon had considerable application prospects in supercapacitors.In summary,the activated carbon materials derived from the waste of MF resin,tobacco stalk and tobacco stalk core had excellent electrochemical properties.Their application feasibility in supercapacitors was demonstrated.At the same time,this work could be a valuable reference for the high-value recovery and utilization of similar wastes.