Capacitive Properties Of Porous Carbons Prepared From Coal Liquefaction Residue

As an effective and clean coal utilization method,direct coal liquefaction technology has been paid more and more attention.In the process,however,about a third of the raw coal will be produced as residue.Coal liquefaction residue（CLR）as a bulk waste,if not effectively treated,not only has a negative impact on the environment but also is a waste of resources.The reuse of CLR is very important to control the cost of the coal liquefaction process.Different porous carbon materials were prepared from CLR and used as electrode materials for supercapacitors to test their electrochemical performance.By constructing different pore structures and doping oxygen atoms,the electrochemical performance of CLR was improved,which proved that CLR could be used as a low-cost precursor for the production of high value-added carbon functional materials.The specific research contents are as follows:（1）Preparation of honeycomb carbon from residual asphaltene by the template method and its capacitance performance.Using asphaltene extracted from CLR as raw material and SiO₂ nano-spheres as a template,carbon materials with honeycomb morphology were formed by carbonization.Then,using KOH as the activator,honeycomb porous carbon materials with the three-dimensional structure were prepared by high-temperature activation.The specific surface area of the sample was 1730 m² g^-1,and the total pore volume was 1.01 cm³ g^-1.At the current density of 1 A g^-1,the specific capacitance is 247 F g^-1.Although the capacitance of the sample without SiO₂ is not significantly improved at the lower current density,the cellular structure can bear the extremely high current density.At the super high current density of 100 A g^-1,the specific capacitance is 185 F g^-1.It still maintains the performance of 75%,after 10000 times of charge and discharge,the ratio of capacitance has almost no attenuation,showing excellent cycling stability.In the supercapacitor device composed of ionic liquid and organic electrolyte as the electrolyte,the samples still maintain good electrochemical performance,and the energy densities are 21.1 Wh kg^-1 and 23.7 Wh kg^-1 at the power density of 10000 W kg^-1,respectively.（2）Preparation of porous carbon from coal liquefaction residue by the self-templating method and its capacitance performance.Because CLR itself contains a lot of ash,its main components are silica-aluminate and other substances,it can also be used as a template in the carbonization process of CLR.In this chapter,CLR is directly used as a carbon source and KOH is used as an activator to prepare hierarchical porous carbon（HPC）containing microporous,mesoporous,and microporous simultaneously through a simple one-step carbonization method.The supercapacitor test results showed that the sample HPC prepared by this template strategy at 700℃ had a specific surface area of 1787 m² g^-1 and a relative conductivity of 19.54 S m^-1.At 1 A g^-1 and 100 A g^-1 current densities,the specific capacitance reaches 250 F g^-1 and 142 F g^-1,respectively,and the performance does not decrease significantly after 10000 charge-discharge cycles.（3）Preparation of oxygen doped porous carbon from coal liquefaction residue by the self-doping method and its capacitance performance.Based on the self-template strategy,a kind of oxygen self-doped hierarchical porous carbon（OHPC）was obtained by pre-carbonization to change the chemical bond between the CLR atoms and by activation with KOH without additional oxidant.The oxidation-reduction reaction of doped oxygen-containing functional groups during the energy storage process increases the pseudo-capacitance.When the activated OHPC was used as electrode material at 600℃,the specific capacitance was 457 F g^-1 at the current density of 0.5 A g^-1.When the current density reaches 50 A g^-1,the specific capacitance remains261 F g^-1.And it has excellent cycle stability,the specific capacitance still maintained 93%after 10000 charge-discharge cycles.Moreover,when the electrolyte is replaced by organic electrolyte and ionic liquid,the supercapacitor has a very high energy density.When the power density is 625 W kg^-1,the energy density is 41.7 Wh kg^-1 and 63.4 Wh kg^-1,respectively.OHPC provides a reference for the application of carbon materials in different systems of supercapacitors.