Structural Regulation And Electrochemical Performance Of Modified Coal Tar Pitch-based Porous Carbon

Supercapacitor,a stable,efficient and low-cost energy storage device,has broad development prospects and attracted wide attention from scientists due to its high power density,long cycle life and friendly environmental.Porous carbons（PCs）are widely used as electrode material for supercapacitors.Their electrochemical properties are usually affected by many factors,such as specific surface area（SSA）,pore size distribution,surface chemical composition and conductivity.Therefore,the development of PCs with high specific surface area,special pore structure and high heteroatom content has become a current research focus.Coal tar pitch（CTP）is a macromolecular substance composed of polycyclic aromatic hydrocarbons（PAHs）.It is extensively used as a carbon precursor for preparing PCs because of its high carbon content,low price and undisturbed by the season.theπ-πinteraction caused by the high degree of polymerization and high aromaticity of the structure hinders the development of CTP-based high-performance carbon materials.Therefore,modification of CTP can improve the molecular polarity of it,which makes it easy to form valence bonds with carbon-based skeletons,activators and templates.In addition,the microscopic morphology,pore structure,electrical conductivity,and surface properties of PCs can be optimized and improved by template and heteroatom doping,which is beneficial to improve the specific capacitance and energy density.In view of above considerations,CTP,as carbon precursor,is modified by different methods to design and construct PCs with reasonable pore distribution and surface properties,which provides a simple and efficient way to develop supercapacitor electrode materials with excellent electrochemistry.The specific research contents are as follows:（1）Hierachical PCs with high SSA are obtained by KOH one-step activation.The micro morphology and pore structure of PCs can be regulated by changing the activation ratio and temperature.The SSA of PC prepared under the optimal conditions is as high as 1993 m² g^-1.When applied as the electrode material,it exhibits excellent rate performance（76.4%）and cycling stability（after 9000 cycles,the specific capacitance is almost unchanged and the coulombic efficiency can still reach 100%）.Furthermore,three-dimensional hierarchical PCs are prepared usinga-Fe₂O₃ as template combined with KOH activation.Micropores produced by KOH activation provide rich active sites.a-Fe₂O₃ can not only play a role of site occupancy,but also can react with C to reduce Fe₂O₃ to Fe-containing species at high temperature,and produces CO₂ for pore formation.These mesopores and macropores provide sufficient channels for electrolyte ion transport.The SSA of HPC-3,prepared under the optimal conditions,is up to 2003 m² g^-1.In 6 M KOH electrolyte,the specific capacitance of HPC-3 reaches 295 F g^-1,and the capacitance retention rate is as high as 97.8%after10,000 cycles.（2）CTP is properly separated into several fractions with relatively narrow molecular size distribution,similar chemical composition and topological structure by organic solvent（carbon disulfide,acetone and ethyl acetate）.The structure and composition of the extract and raffinate are characterized by ultra-high performance liquid chromatography four-stage rod-electrostatic field orbital trap MS and MALDI TOF MS.The results show that carbon disulfide raffinate（CR）exhibits a large planar structure like molecular graphene.Therefore,a simple approach is proposed to prepare layered porous carbon（CRPC）with CR as precursor.The layered structure can not only improve the aspect ratio but also facilitate the transport of electrolyte ions.When CRPC is used as a supercapacitors electrode material,the specific capacitance are 339 F g^-1 at0.04 A g^-1and 273 F g^-1 at 2 A g^-1,respectively.And the capacitance retention rate is81%.The content of PAHs in carbon disulfide extract（CE）is relatively high.The sp²carbon in PAHs is easily rehybridized to sp³ carbon,which is easy to connect with heteroatomic functional groups.Therefore,N/O co-doped three-dimensional honeycomb PCs（NOHPC-x）are prepared by two-stage activation method,using CE as raw material and melamine sponge（MS）as structural framework and nitrogen precursor.In the carbonization process,MS,as the structural skeleton,supports the formation of three-dimensional honeycomb structure and introduces N atoms into carbon skeleton.N atoms with the O atoms introduced during the activation process improve the surface wettability of carbon materials.And the redox reaction occurs to produce pseudo capacitance to enhance the capacitance performance of supercapacitors.NOHPC-3 displays high SSA(2246 m² g^-1),N（up to 3.6%）and O（up to 10.1%）contents.The specific capacitance reaches 302 F g^-1 at 0.05 A g^-1.After 10000 cycles,the capacitance retention is still as high as 99.8%.（3）CTP oxidized by KMn O₄（OCTP）to reduce the accumulation of PAHs,increase the O content of carbon precursor,improve the surface wettability of carbon materials and the accessibility area of electrolyte ions.Three-dimensional porous carbons（3DPC-x）are prepared using OCTP as raw material and Na Cl as a green template.The O-containing functional groups effectively increase the wettability of materials,which provides abundant active sites for electrolyte ions.Additionly,heteroatoms can produce pseudocapacitance through redox reaction.Na Cl is an ionic crystal with a three-dimensional symmetrical structure,which supports the formation of the three-dimensional hierarchical porous structure.The obtained 3DPC-3 displays high SSA(3067 m² g^-1)and O（up to 9.8%）contents.In 6 M KOH electrolyte,the specific capacitance reachs 306 F g^-1 at 0.5 A g^-1,and the capacitance retention rate is as high as 99.7%after 10000 cycles.Futhermore,3DPC-3 electrode gains high working voltage（1.8 V）and energy density(24.8 Wh kg^-1)in 1 M Na₂SO₄.N precursor（OCTP@p PDA）is synthesized by chemical oxidative polymerization derived from OCTP polymerized p-phenylenediamine（p PDA）.There are two-NH₂ at the para position of p PDA molecule.The steric hindrance of-NH₂is small,which is easy to react with the O-containing functional groups of OCTP to form intermolecular-NH,realizing the uniform doping of N.N-doping three-dimensional hydrangea-like porous carbons（NHPC-x）are prepared by OCTP@p PDA as carbon precursor by KOH activation.The grafting of-NH with O-containing functional groups occupies the branch space of PAHs in OCTP,which avoids irreversible accumulation and re-aggregation and supports the formation of three-dimensional hydrangea-like structures.The PC（NHPC-600）prepared under the optimal conditions shows a suitable mesopores porosity（7.6%）and a high N content（3.7%）.When NHPC-600 used as electrode material for supercapacitor,it shows good electrochemical performance in different electrolyte.In 6 M KOH electrolyte,NHPC-600 exhibits excellent capacitance performance(423 F g^-1 at 0.1 A g^-1)and long cycle life.In 1 M Na₂SO₄and EMIMBF₄ionic liquid electrolyte,the working voltage can reach 1.8 V and 3.6 V,respectively.Thus,the energy density is significantly increased to 28.8 wh kg^-1 and 56.3 wh kg^-1.This dissertation contains 94 Figures,26 Tables and 298 references.