Preparation Of Porous Carbons And Their Supercapacitor Performance Studies

As a new type of energy storage/conversion devices,supercapacitors have numerous advantages over traditional batteries,such as excellent charge-discharge performance,good repeatability and recycling performance.Supercapacitor can be divided into electrical double-layer capacitors(EDLCs)and pseudocapacitors based on the mechanism of energy storage.Compared with pseudocapacitors,EDLCs possess longer cycle life,higher power density but lower capacitance value,which make them occupy an important place in the commercial capacitors.However,most of the EDLCs confront the problem of low energy density,so developing advanced materials with high capacitance for EDLC is a significant factor.Porous carbons are the most used materials for EDLCs.Porous structures can be divided into micropores,mesopores and macropores according to the pore size.Micropores attribute large surface area and abundant activated sites but are difficult in accessing electrolyte ions at a high current density.On the contrary,mesopores are dominant in accelerating ion migration to obtain higher capacitance than micropores.Herein,we reported the carbons activated by different methods and adding other elements to obtain the electrode material of high performance with the advantages such as large surface area,appropriate pore structure and low-cost.Meanwhile,the prepared materials were characterized by SEM,TEM,N2 adsorption-desorption technique,XRD,Raman and XPS.Their electrochemical performance was investigated using an electrochemical workstation.The detailed works were summarized as follows:1.A facile method free of activation agents to synthesize porous carbons with high sueface area(AACS)by air-assisted activation using RF as the precursor without inert atmosphere.We studied the influence of activation time on porous strtucture,and revealed that the mesopore percentage increased with the increase of activation time.The optimal sample AACS-6 had the highest Brunauer-Emmett-Teller surface area of 2178 m2 g-1and the biggest pore volume of 1.01 cm3 g-1.The electrochemical performance demonstrated that the AACS-6 electrode had a large specific capacitance of 222 F g-1 at 0.5 A g-1 and excellent rate capability of 87.5% at 20 A g-1 in a three-electrodesystem.Morever,AACS-6 electrode also showed excellent cycling stability with a 97% retention of the intial capacitance after 5000 cycles,and the assembled symmetrical cell had a high energy density of 10.1 Wh kg-1at a power density of 398.7 W kg-1.2.The porous carbons were derived from torreya grandis shell by means of carbonization and KOH activation under N2,which possessedmacroporous morphology,large surface area,and wonderful electrochemical performance.It was proved that the pore structre could be optimized by adjusting the temperature and KOH ratio.The sample AC-800-3 which was activated in 800 oC and 3 times of KOH had a maximum specific surface area of 2100.8 m2 g-1 and good micropore/mesopore structure.The electrode realized a high capacitance of 290.5 F g-1 at 0.5 A g-1 and excellent rate capability of 62.6% in three-electrode system.The assembled symmetrical cell exhibited a high energy density of 13.5 Wh kg-1 at a power density of 360.1 W kg-1 and excellent cycling stability with 93.1% retention of the initial capacitance after 5000 cycles.3.The N-doped porous carbons with superior mesoprosity were prepared by using SBA-15 as the hard template,furfuryl alcohol as the carbon precursor and melamine as the nitrogen source.The sample ANMC-2,which was activated at 800 oC and 2 times of KOH,had a largest specific surface area of 2277.7 m2 g-1 and a nitrogen content of 3.84%.Furthermore,the electrochemical performance indicated that a maximum specific capacitance value of 292.6 F g-1 at 0.5 A g-1 and excellent rate capability of 82.7% at 20 A g-1 were obtained.It also exhibited excellent cycling stability(98.5% retention after 5000 continuous charge-discharge cycles).Meanwhile,the assembled symmetric cell delivered a maximum energy density of 14.8 Wh kg-1 at a power density of 359.3 W kg-1.