| Recently,the super capacitors have been received a great interest as very powerful and advanced energy storage device in portable electronic units,power backups,electrical vehicles,stationary energy storage,etc because of their excellent cyclic durability,quick charge-discharge rate,co-friendly,low-cost and ultrahigh power density than that of other energy storage devices.Nevertheless,the major disadvantages of supercapacitors are their limited energy density,which is extensively hindered their industrial application.Thus,in order to raise the energy density of supercapacitors,it is an urgent task on the development of efficient and new-kind of electrode materials for supercapacitors.The porous carbon is played a major role as effective electrode for supercapacitors in recent time owing to its huge specific surface area,long cyclic stability,large porosity and better electrical conductivity.Especially,the porous carbons derived from naturally available biomass wastes have great interest as electrode materials for supercapacitors due to their extremely inexpensive,co-friendly and more sustainable porous carbon materials.Even though the capacitive and cyclic durability of biomass derived PC materials are still lower as compared with chemically synthesized porous carbon materials due to their limited electrochemical active sites and adsorption ability.In this regard,it is most urgent to derive new biomass porous carbon with large surface area and high electrochemical properties for supercapacitor.Therefore,in the present investigation,we have concentrated the design and prepare three new porous carbons via selecting(1)waste mangosteen peel,(2)jujube fruits and(3)feather finger grass's flower as biomass carbon precursors via combined carbonization followed by chemical activation processes for supercapacitor applications.These as-prepared carbon materials were further characterized by different characterization techniques like SEM,HR-TEM,XRD,Raman spectroscopy,BET,XPS,element mapping,and TGA analyses.The electrochemical properties of these porous carbons were investigated initially from CV and GCD tests using three-electrode setup in 6 M KOH as electrolyte.Afterwards,the electrochemical properties of these porous carbons were assessed in two-electrode system via fabricating symmetrical coin-like supercapacitors.The results obtained from these three porous carbons are clearly described in below.(1)We proposed a porous carbon from waste mangosteen peel as precursor via a facile combined method of carbonization and NaOH treatment processes.The obtained mangosteen peel porous carbon(MP-PC)has a large surface area of 2,623 m2 g-1 and displays a stone-like morphology with highly ordered hierarchical meso-pores structure.The MP-PC offers a superior specific capacitance(357 F g-1 at 1 A g-1)and an outstanding rate performance(190 F g-1 at 100 A g-1)with very low decline rate of 5.5%capacitance after 130,000 cycles at ultra-fast current density of 50 A g-1.Furthermore,this MP-PC based symmetrical supercapacitor with 1 M Li2SO4 electrolyte provides a high energy density of 17.28 Wh kg-1 at 401 W kg-1 with keeps 80%of capacitance for 10,000 cycles at 20 A g-1.Similarly,the symmetrical supercapacitor with 1 M Et4NBF4/AN organic electrolyte also delivers a high energy density of 16.69 Wh kg-1 at 631 w kg-1 and with retains 84%of capacitance over 10,000 cycles at 20 A g-1.Therefore,this work is providing an important strategy for the reusing of the waste mangosteen peels and a new method for the preparation of a low-cost energetic material for high performance supercapacitor.(2)We designed a highly porous natural carbon from renewable and inexpensive jujube fruits by pre-carbonization followed NaOH activation approaches.The specific surface area of the prepared jujube porous carbon(JPC)is increased from 85.4 to 1135 m2 g-1 after the completion of NaOH activation.The electrochemical results demonstrate that JPC displays the specific capacitance of 460 and 324 F g-1 at 1 and 100 A g-1,respectively with capacitance retention of 92.2%after 130,000 cycles at 50 A g-1.Moreover,the assembled symmetrical coin-like supercapacitors with 6 M KOH electrolyte shows a high energy density of 22.7 Wh kg-1 at 368 w kg-1 with remaining 63%capacitance over 10,000 cycles at 30 A g-1.Meantime,the assembled symmetrical supercapacitors with wide potential window of 2.5 V in 1 M Et4NBF4/AN organic electrolyte offer a high energy density of 23.7 Wh kg-1 at 629 w kg-1 with remaining 94%capacitance over 10,000 cycles at 30 A g-1,indicating its practical application prospect.As a result,the present study proves the natural jujube fruits are a promising sustainable carbon source for making more economical and efficient electrode material of high performance supercapacitors.(3)We prepared a new hollow tubular-like porous carbon(HT-PC)from the freely available feather finger grass flower(FFGF)via combination of carbonization and KOH activation treatments.The as-prepared biomass HT-PC containing the different sized micro-pore arrangement with a huge surface area(637.1 m2 g-1),The as-prepared HT-PC provides a remarkable specific capacitance of 315 F g-1 at 1 A g-1 and 262 F g-1 at 100 A g-1 with keep 96%of capacitance over 50,000 cycles at 50 A g-1 using 6 M KOH aqueous electrolyte.In addition to that,the HT-PC electrode based symmetrical supercapacitor releases a high energy density of 18.75 Wh kg-1 at 370 w kg-1 with losing 30%of capacitance over 10,000 cycles at 10 A g-1 using 6 M KOH electrolyte.Meanwhile,the symmetrical supercapacitor shows a good energy density of 13.18 Wh kg-1 at 610 w kg-1 without losing any capacitance over 10,000 cycles at 10 A g-1 using 1 M Et4NBF4/AN electrolyte.As the results,this study is verified that the naturally available FFGF is a talented sustainable carbon source to make more economical and effective carbon electrode for supercapacitors.Overall,these findings demonstrate that as-prepared natural porous carbons are potential candidates as low-cost and environmental friendly electrode material for energy application. |
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