Preparation Of Coal-based Microcrystal Porous Carbon And Its Adsorption And Capacitance Performance

The excessive consumption of non-renewable energy makes a series of environmental and energy problems.The development of efficient energy storage materials and adsorption materials has far-reaching significance for alleviating the fossil energy crisis and protect the ecological environment.Carbon-based solid materials are one of the most important materials in the fields of environment protection,supercapacitor energy storage,and advanced structural materials,due to excellent physical and chemical properties and rich forms of existence.However,the pore-making temperature of carbon structure(<1000 ℃)is much lower than its graphitization temperature(>2000 ℃),there still are some defects in practical applications,such as in the field of supercapacitors,which seriously limit the power density of capacitors due to low graphitization degree and poor conductivity.In the field of carbon dioxide adsorption,too much pores in the material seriously reduce the pore utilization ratio and mechanical strength of the material.The application of porous carbon in the adsorption of molecules/ions is the adsorption,storage,transportation and release of molecules/ions in the pores.In the application of carbon dioxide adsorbent and capacitor,it is essentially adsorbed molecules or ions,transportation,and the reaction in the pore structure.Therefore,the pore characteristics,graphitization characteristics and structural defects(heteroatom doping)of the materials will affect the transport of molecules/ions.Generally,carbon-based adsorption materials should have ordered pore and stable carbon skeleton structure.Coal is a carbon-based macromolecule with dense and ordered structure.During pyrolysis and carbonization,the aromatic structure in coal is depolymerized and condensed,resulting in the mutual transformation of crystal sp2 hybrid carbon,isolated sp2 hybrid carbon,amorphous sp2 and sp3 hybrid carbon.Hybrid aromatic structures sp2 coal provide an ideal structural for constructing high-performance carbon-based adsorption materials.Therefore,based on the hybrid structure transformation of aromatic carbon in coal,a catalytic carbonization-activation method is proposed to prepare coal-based porous carbon materials to enhance the conductivity and structural stability of porous carbon.And then improve its capacitance characteristics and carbon dioxide adsorption stability.The specific studies are as follows:1.The coal of Meihuajing was prepared as raw material,nickel nitrate was added to the coal preparing catalytic graphitization carbon graphite precursor.The graphitization process condition is 15%catalyst addition,carbonization temperature 900℃,and carbonization time 90 minute.Then using KOH as activator,the activation conditions is KOH:coal=3:1,activation temperature is 850～950℃.Finally,coal-based graphite microcrystalline porous carbon materials(KDC-90)were prepared by catalytic-activation coupling with graphitic carbon as precursor.The material was used as an adsorbent,the amount of carbon dioxide adsorption could reach 5.24 mmol·g-1 at 0℃,and after 10 cycles of adsorption/desorption,the capacity retention is 95%.The specific capacitance of KDC-90 in a three-electrode system with 6 mol·L-1 KOH electrolyte is 200 F·g-1 at the current density of 0.1 A·g-1,and the capacitance retention is 95%after 20000 cycles at the current density of 0.2 A·g-1.2.Based on the similarity temperature range between catalytic graphitization and activation,one-step catalytic activation was used to prepare coal-based graphite microcrystalline porous carbon material(YC-40).Under the condition of 15%catalyst and KOH:coal=3:1,activated at 900℃ for 40 minute,the obtained porous carbon material has a specific surface area of 2885 m2·g-1 and the pore size distribution of 2.6 nm.As CO2 adsorbent,the adsorption capacity of porous material is up to 5.09 mmol·g-1 at 0℃,after the 10 cycles of adsorption/desorption,the carbon dioxide adsorption capacity retention is 95%.The specific capacity of YC-40 in a three-electrode with 6 mol·L-1 KOH electrolyte,is 230 F·g-1 at the current density of 0.1 A·g-1 and after 20000 cycles the capacity retention is 94%at the current density of 0.2 A·g-1.Compared with the coal-based porous carbon prepared by the activation method,the cycle stability and rate performance of graphite microcrystalline porous carbon are improved,its capacity is twice that of porous carbon at a current density of 5 A·g-1.3.The carbon nanotube/coal-based porous carbon composite material(N,O-PC-CNTs)was obtained by self-assembly of ionic liquid.The content of macropores and mesopores in the porous carbon was increased by carbon nanotubes.The composite material has hierarchical pore structure.As well as nitrogen and oxygen atoms in the ionic liquid were doped into the composite material by pyrolysis.As CO2 adsorbent,the composite material has an adsorption capacity up to 5.68 mmol·g-1 at 0℃,and the adsorption capacity retention rate after ten cycles is 94%.The specific capacity of carbon nanotube/coal-based porous carbon composite material is 287 F·g-1 at current density of 0.2 A·g-1.When the current density increased to 10 and 50 A·g-1,its specific capacity retention rates are 70%and 64%.The results show graphite structure can significantly improve the rate performance of the porous carbon.Notably,the material used as symmetrical supercapacitor electrode in an alkaline liquid circulation system capacity retention rate is up to 95%after 20000 cycles.