Research On Preparation And Electrochemical Properties Of Hierarchical Porous Carbon Materials Based On Loose Medium Component Separated From Coal

Loose medium component separated from raw coal by all group components separation method was used to prepare hierarchical porous carbon materials by reactivation method and template method respectively.The effects of preparation process conditions on pore structure and electrochemical performance were investigated.The evolution process of graphitization degree and micro morphology of the hierarchical porous carbon materials were analyzed.Finally,the pore forming mechanisms of reactivation method and template method were deeply explored.The results show that:the hierarchical porous carbon materials prepared by reactivation method with ZnCl₂ used as first-step activation agent and KOH used as reactivation agent possessed ultra-high specific surface area.When the first-step activation temperature was 500°C,activation agent ratio was 2:1,and activation time was 1 h,the specific surface area of the sample can reach 4672 m²/g and specific capacitance was 233 F/g at 5 A/g.The appropriate activation agent ratio was beneficial to the formation of mesopores while the superfluous ZnCl₂ may cause defects and collapse of pore structure.The activation reaction cannot be carried out effectively at a lower temperature and excessive temperature would result in the increased erosion effect of ZnCl₂ and destroy the pore channels.If activation time was too long or too short,pore structure would decay to a certain extent,and activation effect was the best at 1 h.During the activation process,ZnCl₂ worked as the acceptor center of electron pair to react with-OH and-NH₂.The relatively well-developed micro-and meso-porous structure was developed via the fracture of intermolecular hydrogen bonds.While,on the basis of the existing pore structure,on the one hand,more abundant micropores was etched by the reactivation of KOH,on the other hand,the existing microporous structure was expanded by the pore-widening function of KOH reactivation,so as to effectively increase the mesopore content and realize the effective construction of hierarchical porous structure.Carbon nanosheets with hierarchical porous structure was successfully prepared with layered nano-MgO as template and structure-directing agent,loose medium component as carbon source,and KOH as activation agent.Along with the increase of template dosage,the micro morphology gradually changed from disordered foam structure to ideal two-dimensional layered structure,the graphitization degree increased obviously,and the rate performance improved continuously.While with the increase of KOH/carbon ratio,the microporous structure became more and more developed,proportion of mesopores was more suitable,and pore size distribution tended to be ideal.When the template dosage was 5 g and KOH/carbon ratio was 6:1,the prepared sample possessed an ideal graphene-like 2D layered structure,high graphitization degree,and well-developed hierarchical porous structure,while the specific capacitance can come up to 262 F/g at 10 A/g and the rate performance can reach 72%.During the pore-forming process,nano MgO not only played an important role as the template of mesopores and macropores,meanwhile,aromatic hydrocarbon molecules featuring sp² carbon atoms gradually transformed into 2D crosslinking lamellar structure through the polymerization and aromatization.In addition,KOH can produce abundant microporous structure on carbon nanosheets by in-situ synchronous activation,so as to achieve the effective construction of hierarchical porous structure.