Preparation And Electrochemical Performance Of Interconnected Porous Carbons From Coal Tar Pitch

With the fast development of industrialization process,the demand for energy and fossil fuels is increasing.However,the depletion of non-renewable energy sources,e.g.coal,oil and natural gas,will undoubtedly have a serious negative impact on the environment.In order to solve the above mentioned problems,it is extremely urgent to seek green energy sources.For the sake of making full use of renewable energy sources,e.g.wind energy and solar energy,electrochemical storage devices have attracted much attention.Supercapacitor is a new type of energy storage device with the advantages of fast charge rate,high power.The performance of supercapacitors primarily depends on the electrode materials.Activated carbon is one of the most widely used carbon materials for supercapacitors.The preparation of carbon electrode material from low-cost coal tar pitch not only reduces the cost and the pollution to the environment,but also improves the high added value utilization of chemical by-products.Therefore,coal tar pitch is used as the carbon source to prepare interconnected porous carbons by template strategy combined with chemical activation method.The main conclusions are as follows:（1）Coal tar pitch,nano-Ca CO₃ and K₂CO₃are used as carbon source,template and activator,respectively.Interconnected porous carbons are prepared at 850°C by conventional heating method and named as IPC_X,x represents the mass ratio of activation agent to carbon source.When the mass of carbon source,template and activation agent is 2 g,4 g and 12 g,respectively,the specific surface area of as-prepared IPC₆ is the highest up to 933 m² g^-1,indicating that the pore structure of porous carbons can be tuned by changing the mass ratio of activation agent to carbon source.XPS test results show that all samples contain C and O elements.Scanning and transmission electron microscopy results exhibit that the samples are interconnected sheet-like structure,which can shorten the ion transfer distance.The specific capacitance of IPC₆ electrode is 225 F g^-1 at 0.05 A g^-1;the specific capacitance of IPC₆ electrode is 150 F g^-1 at 40 A g^-1.At 5 A g^-1,the specific capacitance only decreases by 1.09%after 10000 cycles.（2）Based on the above experiment,coal tar pitch,nano-Ca CO₃ and K₂CO₃are used as carbon source,template and activation agent,respectively.Nitrogen-doped interconnected porous carbons are prepared by changing the final heating temperature using ammonia as a nitrogen source.The nitrogen-doped interconnected porous carbons prepared by chemical activation method are named as NIPC_X,x represents the final heating temperature.XPS test result shows that NIPCs have three kinds of elements,e.g.C,O,and N.Furthermore,a certain amount of nitrogen（1.83%）and oxygen（4.42%）functional groups can improve the surface wettability of carbon materials.The specific surface area of NIPC₈₀₀ is 1310 m² g^-1.The specific capacitance of IPC₆ electrode is 225 F g^-1 at 0.05 A g^-1.At 5 A g^-1,NIPC₈₀₀ exhibits excellent cycling durability of 96.12%,after 10000 cycles.（3）Based on the above experiment,Nano-Ca CO₃ is replaced by sodium thiosulfate.Sodium thiosulfate is used as the template,activation agent and sulfur source.Nitrogen/sulfur co-doped interconnected porous carbons with different structures and properties are prepared by changing the final heating temperature.The as-prepared sample is named as NSIPCx,x represents the final heating temperature.NSIPC₈₀₀ possesses a high surface area(2000 m² g^-1).XPS results show that N and S are successfully incorporated into the porous carbons.Furthermore,a certain amount of nitrogen（0.99%）and sulfur（0.43%）functional groups can improve the surface wettability of the carbon materials.NSIPC₈₀₀has a superior specific capacity of 302 F g^-1 at 0.05 A g^-1,high rate capability of 230 F g^-1 at 40 A g^-1.This synthetic method avoids the acid washing step,simplifying the preparation process,saving cost and protecting environment.