The Study On The Supercapacitor Performance Of Selenium Or Nitrogen Doped Activated Carbon With Ultra-high Specific Surface Area

Compared with secondary batteries,supercapacitors play a huge role in the transformation of wired power grids into mobile power supplies due to their advantages of high-energy conversion efficiency,fast charging and discharging speed,high-power density and strong cycle stability.Carbon materials are the most widely used electrode materials in supercapacitors and still have a lot of room for improvement.In this paper,the development and modification of activated carbon with ultra-high specific surface area and its application in supercapacitors are the research goals.Different doping methods are used to prepare activated carbon with heteroatom doping,high specific surface area and developed pore structure through experimental design.The heteroatom distribution,valence state,specific surface area and pore size distribution of the prepared activated carbon were characterized by XPS,SEM,TEM,BET,Raman,etc.The electrochemical performance was measured by cyclic voltammetry,constant current charge-discharge and AC impedance.The influence of heteroatom doping,specific surface area,pore size distribution and morphology factors on the performance of ultra-high specific surface area activated carbon were studied.The main research results of this paper are as follows:（1）The rice husk activated carbon（RHAC）were prepared by using rice husk as the carbon precursor and KOH as the activator.The effects of different pretreatment methods on the specific surface area,pore structure and morphology of RHAC were studied.Its physicochemical and electrochemical properties were characterized and discussed.The results showed that the rice husk carbon（RHAC-b）prepared by the pretreatment of10wt%K₂CO₃solution had the highest specific surface area of 2556.8 m²/g,and the largest pore volume of 1.2732 cm³/g with a developed micro/mesoporous structure.The electrochemical test results in 6 M KOH electrolyte show that at a current density of 0.5A/g,the first discharge specific capacity of RHAC is 325 F/g,and the specific capacity retention rate after 10,000 cycles of charging and discharging is 87.7%.（2）The in-situ Se-doped rice husk activated carbon（Se-RHAC）were prepared and characterized by using Se-enriched rice husk as the carbon precursor and KOH as the activator,and its physicochemical properties and electrochemical properties were discussed.The results show that the specific surface area of Se-RHAC is 3360.2 m²/g;the pore volume is 2.0647 cm³/g;the Se content is 0.37%;and the Se mainly exists in the form of selenide.The electrochemical test results in 6 M KOH electrolyte show that at a current density of 0.5 A/g,the first discharge specific capacity of Se-RHAC is 355 F/g,and the specific capacity retention rate after 10000 cycles of charging and discharging is97.1%;and the specific capacity retention rate is 76.1%at a high-current density of 10A/g.（3）The shaddock peel activated carbon（SAC）were prepared and optimized by using shaddock peel as the carbon precursor and KOH as the activator.The effects of different activation temperature and alkali-carbon ratio on the specific surface area and pore structure of SAC were studied.The morphology and structure of SAC as well as its physicochemical and electrochemical performance were studied.The results show that with the increase of activation temperature and alkali-carbon ratio,the specific surface area of SAC first increases and then decreases.When the activation temperature is 800℃and the alkali-carbon ratio is 4:1,the activation gets the best effect with a specific surface area of at 3252.9 m²/g and a pore volume at 1.2732 cm³/g.The electrochemical test results in 6 M KOH electrolyte show that at a current density of 0.5 A/g,the specific capacity of SAC is 315 F/g for the first discharge,and the specific capacity retention rate after 10,000 cycles of charging and discharging is 87.6%.（4）The N-doped shaddock peel activated carbon（N-SAC）were prepared by using SAC as the object and urea as N source,the effects of calcination temperature and urea addition on the specific surface area and pore structure of N-SAC were investigated.The morphology and structure of N-SAC as well as its physicochemical properties and electrochemical properties were discussed.The results show that the N-SAC-3 prepared on the urea-SAC ratio at 3:1 has the highest specific surface area of 2450.6 m²/g,and its N content is 4.12%.Hetero N element exists in the form of C-N bonds,including pyridine N,pyrrole N,graphitic N and oxynitride.The electrochemical test results in 6 M KOH electrolyte show that at a current density of 0.5 A/g,the specific capacity of N-SAC-3 is 357 F/g for the first discharging,and the specific capacity retention after10,000 cycles of charging and discharging is 89.9%.（5）N-doped TPU activated carbon（TPUC）were prepared with self-made polyurethane as the carbon precursor and KOH as the activator.The effects of different activation temperatures on the specific surface area,pore structure,and N content were studied,and the morphology and structure of TPUC were characterized.Its physicochemical and electrochemical properties were discussed.The results show that with the increase of activation temperature,the specific surface area first increases and then decreases,and the best activation effect was achieved at 800℃with a specific surface area of 3575.5 m²/g,a pore volume of 2.0393 cm³/g,and a N content at 2.54%.The doped N were mostly observed in the C-N formation,along with other pyridine N,pyrrole N,graphitic N and oxynitride.The electrochemical test results in 6 M KOH electrolyte show that at a current density of 0.5 A/g,the specific capacity of TPUC-800 is527 F/g for the first discharging,and the specific capacity remained at 342.5 F/g after10,000 cycles of charge and discharge;at a large current density of 10 A/g,the specific capacity is still 273.9 F/g.（6）The specific surface areas of 300-Se-RHAC,300-SAC and 300-TPUC are 3101m²/g,3165.4 m²/g and 3252.9 m²/g,using selenium-rich rice husk,shaddock peel and self-made polyurethane as carbon precursors,respectively.The electrochemical test results in 6 M KOH electrolyte show that at a current density of 0.5 A/g,the first discharge specific capacity of 300-Se-Rhac,300-SAC and 300-TPUC are 348 F/g,312F/g and 480 F/g,respectively,and the specific capacity retention rate after 10,000 cycles of charging and discharging are 334 F/g,270 F/g and 339 F/g,respectively,at a large current density of 10 A/g,the specific capacity are 261 F/g,228 F/g and 285 F/g,respectively.