Preparation And Electrochemical Performance Of Hierarchical Porous Carbon-Based Electrodes In Supercapacitors

Supercapacitors have been developed as novel energy storage devices between traditional capacitors and batteries,and bridge the gap between batteries and conventional capacitors.Compared with traditional capacitors and batteries,supercapacitors show high energy density and high power density,respectively.And then the supercapacitor has received increasing attention in the field of energy storage.It is well known that the electrode is an important component of supercapacitor,and also is a critical factor that influences supercapacitor performance.According to the storage mechanism of electrochemical double-layer capacitors,the best method for improving the supercapacitive performance is to prepare electrode material with high surface area and well-developed hierarchical pore structure.Then,this paper aim to fabricate the electrode of supercapacitor with well-developed pore structure,and the main research works and results are list as following:The micro-and nano-carbide derived carbons(micro-CDC,nano-CDC)both with hierarchical pore structure are prepared by high-temperature catalyzing and KOH activating microporous CDC,respectively.And the effects of different treatment on the pore structure,as well as supercapacitive performance,have been systematic studied.And the results show that,the amorphous structure of micro-CDC near the catalyst can be transformed into ordered structure at high temperature.This ordered structure micro-CDC leads to the formation of mesopores around 3.8 nm.The specific surface area(SSA)of catalyzed micro-CDC has little decrease(from 2029 m2 g-1 to 1822 m2 g-1).And the specific capacitance of catalyzed micro-CDC is similar to that of pristine micro-CDC.But,the rate performance of catalyzed micro-CDC with hierarchical pore structure is highly improved,it cyclic voltammogram(CV)curves can keep a rectangular-like shape even at a scan rate of 500 mV s-1.Comparatively,the KOH activation leads to the increase of SSA of nano-CDC(from 1531 m2 g-1 to 2265 m2 g-1)and the formation of mesopores with pore size between 2 and 5 nm.Due to the higher SSA and wider mesopore size,the KOH activated nano-CDC(ACDC)shows more outstanding supercapacitive performance than catalyzed micro-CDC.The specific capacitance of ACDC is 141 F g-1,higher than catalyzed micro-CDC(95 F g-1),at a scan rate of 5 mV s-1 in KOH electrolyte.The ACDC also shows excellent rate performance,its CV curves can keep a rectangular-like shape even at a scan rate of 5000 mV s-1.In order to explore the carbon-based supercapacitor electrode with better electrochemical performance,the graphenes(RGO and GNS)with different preparation methods(chemical exfoliation and liquid-phase exfoliation)were used as electrode active materials,respectively.And the RGO/ACDC composites and GNS/ACDC composites both with hierarchical pore structure were successful produced by using ACDC as spacer.And the results show that,ACDC successfully inhibits the agglomeration of graphene and opens the space between graphene sheets for the transport of electrolyte ions.Then,both the surface of graphene and the well-developed pore structure of ACDC in the graphene/ACDC composites are accessible to electrolyte ions.In addition,due to the difference in structure of RGO and GNS caused by different preparation methods,the RGO/ACDC composites and GNS/ACDC composites show different supercapacitive performance.The highest specific capacitance of RGO/ACDC composites is 195 F g-1 at a scan rate of 5 mV s-1,and its cyclic voltammogram curves can keep a rectangular-like shape even at a scan rate of 5 V s-1.However,compared with RGO/ACDC composites,GNS/ACDC composites show lower specific capacitance(168 F g-1).But,GNS/ACDC composites exhibit excellent rate performance,when the scan rate up to 20 V s-1,its CV curves can also keep a rectangular-like shape.To further improve the supercapacitive performance of graphene/ACDC composites,the N-doped porous graphene(NPG)and F-doped porous graphene(FPG)were successfully prepared by KOH etching and hydrothermally adulteration.The pores in graphene can provide more ions transport channels which are perpendicular to graphene plane,and the N or F functional groups can offer pseudocapacitance.As expected,the specific capacitance of NPG/ACDC composites and FPG/ACDC composites are obviously increase to 328 F g-1 and 321 F g-1,respectively.These two composites also show excellent rate performance,its shapes of CV curves can not distort at high scan rate(500 ~ 1000 mV s-1).NPG/ACDC composites and FPG/ACDC composites are both show remarkable long-term cycling stability.Its specific capacitance is quite stable over the entire cycle numbers,and has no decay in specific capacitance even after 10000 cycles.