Preparation And Performance Improvement Of Activated Porous Carbon Materials For Supercapacitors

Supercapacitors,which are also known as electrochemical capacitors or ultracapacitors,have attracted a great deal of attention from both industry and academia due to their high power density,rapid charge/discharge rate,long cycle life,fast dynamics of charge propagation etc.As we all known,the electrode material is a key factor to influence on the performance of supercapacitors.Among different types of electrode materials including various carbon materials,transitional metal oxides and conducting polymers,porous carbon with nanoarchitecture electrode materials are considered as the most promising materials for practical supercapacitors.It can be attributed to their high specific surface area,well-developed pore structrue,superior electrical conductivity,good stability,convenient synthetic procedure and low cost.In this paper,hollow porous carbon spheres(HPCSs)with micro/mesoporous combination shell and macroporous core have been successfully synthesized by hydrothermal method employing silica as the template,and further activated by KOH to leading to a large active surface area and pore volume.In order to further optimize the supercapacitive performance of the AHPCSs,the electrochemical behaviors of the AHPCSs supercapacitors in different electrolytes are evaluated,and the results are meaningful.Moreover,nitrogen and sulfur co-doped carbons derived from chromium carbide(NSCDC)are successfully synthesized by chemical extraction method and hydrothermal treatment to improve the conductivity,wettability of the CDCs.The main work in this paper is as follows:(1)HPCSs are prepared through template method and hydrothermal treatment in which furfuryl alcoho1 and silica nanospheres are used as carbon source and hard template,respectively.The physical and electrochemical properties of the HPCSs prepared by adjusting the proportion of carbon source and silica template are investigated in detail.Furthermore,KOH activation is used to introduce more micropores and mesopores in the shells,leading to a large active surface area and pore volume,and the the influence for supercapacitor performance is studied.The results show that the HPCSs-2(the mass ratio of FA/ silica is 2/1)possess the optimal morphology structure and electrochemical properties.In addition,AHPCSs maintain the hierarchical porous hollow structure,and the specific surface area is enlarged to 1290 m2 g-1.The AHPCSs treated with KOH obtains the specific capacitances of 249.6 F g-1 at the scan rate of 5 mV s-1 and 303.9 F g-1 at the current density of 1 A g-1.Furthermore,the AHPCSs supercapacitor still keeps the specific capacitance of 72.7 F g-1 even after 5000 cycles.(2)In order to optimize the supercapacitive performances,the eletrochemical properties of the of the AHPCSs supercapacitor in 1-ethyl-3-methylimidazolium tetrafluoroborate(EMIMBF4)ionic liquid electrolyte,1 mol L-1 LiPF6 organic electrolyte and 6 mol L-1 KOH aqueous electrolyte are evaluated.The results demonstrate that the supercapacitors perform definite supercapacitive behaviors;especially in EMIMBF4 ionic liquid electrolyte,the supercapacitor represents a specific capacitance of 64.4 F g-1 at current density of 0.5 A g-1,which can be charged/discharged at an operating voltage of 3.0 V.As a result,a high energy density of 80.5 Wh kg-1 at the power density of 750 W kg-1 is achieved.Furthermore,the capacity retention of the supercapacitor is as high as 94.2 % over 4000 cycles and the the coulombic efficiency is almost 100%.(3)Nitrogen and sulfur co-doped carbons derived from chromium carbide(NSCDC)are successfully synthesized by chemical extraction of chromium atom from chromium carbide and followed by a facile hydrothermal treatment using thiourea as nitrogen and sulfur sources.The supplementary pseudocapacitance and enhanced wettability as well as the improved conductivity are believed to be responsible for the excellent capacitive performance of NSCDC materials.The maximum specific capacitance of 281.2 F g-1 at the scan rate of 1 mV s-1 can be achieved for the NSCDC-4.The supercapacitor using NSCDC-4 as electrode material holds high specific capacitance retention of 95 % after 6000 cycles.