Preparation And Electrochemical Performance Of Porous Carbon-graphene Composites

Among various energy store devices,supercapacitors have attracted considerable attentions ascribing to their fast charge/discharge,long life cycle,high power density,environment friendly and many other advantages.As the key part of supercapacitors,the performance of electrode materials has significant influence on the specific capacitance.In this paper,porous carbon and carbon-graphene composites were prepared using petroleum pitch and phenolic resin as carbon precursors,characterized by SEM,TEM,XRD,N₂ adsorption/desorption,IR,Raman techniques and their electrochemical performance was evaluated.Porous carbon materials were prepared by using petroleum pitchfrom as carbon precursor and calcium carbonate as hard templates,which produced many pores using itself placeholder and pyrolysis at the carbonization temperature of 650⁹50?.The study shows that the carbonization temperature has a great influence on the structure and morphology of porous carbon.And the PC-CaCO₃-850 porous carbon material prepared at the temperature of 850?has the best performance,which is made up of porous layers in order and has a large specific surface area,rich micropore and reasonable distribution of pore structure.PC-CaCO₃-850 has a good capacitive performance in the three-electrode system,including high specific capacity(267 F g^-1at the current density of 0.5 A g^-1)and stable cyclicity(85.7%retained after 5000cycles at the current density of 10 A g^-1).Both the CV curves and the GCD curves show the allusion type capacitance behavior in the two-electrode system.A facile one-step method was developed to fabricate hierarchically porous carbon-graphene composites,which exhibited superior electrochemical performance in supercapacitor as electrode.The preparation was processed at a temperature range of 650–950?using phenolic resol as carbon source,alkali chloride?LiCl,NaCl and KCl?salt as salt templets.The structural and morphological characterizations showed that composites possessed a special 3D structure,which consisted of well-dispersive porous carbon growing chemically on the graphene sheets.The porous carbon served as spacers to block the aggregation of graphene sheets.This unique structure benefited the penetration/mobility of ions within the composites due to high surface area,abundant micropores/mesopores/macropores,high conductivity of graphene,and strong chemical interaction between porous carbon and graphene.The optimal sample in the three series of composite materials are PCG-LiCl-750,PCG-NaCl-750 and PCG-KCl-750 respectively,which are prepared at the temperature of 750?,and PCG-KCl-750 has the most outstanding electrochemical performance in the three-electrode system including high specific capacitance(341 F g^-11 at the current density of 0.5 A g^-1),excellent rate capability(69.5%capacitance retention at current densities up to 20 A g^-1),and stable cycling performance(95.2%retained after 5000cycles at the current density of 10 A g^-1).It also has good electrochemical performance in the two-electrode system.