Preparation Of Biobased Self-doped Oxygen-rich Porous Carbon And Its Electrochemical Capacitors Performance

Energy storage and conversion is one of the greatest challenges of the 21st century.In order to meet the needs of modern society,it is important to develop an efficient energy storage device.Supercapacitors have been widely studied by scientists due to their advantages of high power density,fast charge-discharge speed and long cycle life.As one of the core components of supercapacitor,electrode material determines the performance of supercapacitor.An excellent electrode material needs to have high usable specific surface area and developed pore structure,as well as suitable heteroatom doping and good electrical conductivity and other characteristics.Therefore,the development of low cost and high performance porous carbon has become a hot topic today.In this paper,a simple and effective method to prepare high-performance electrode materials for supercapacitors was proposed.By using magnesium acetate to activate biomass to obtain heteroatomic self-doped superhydrophilic porous carbon materials.Two biomass derived porous carbon were prepared by this method,their physical properties and electrochemical properties were studied.The main research contents are as follows:（1）Oxygen-rich porous carbon EMC-n-x was prepared by using Enoki mushroom which was rich in heteroatoms（O,N）as carbon precursors.The soluble components were first soaked in ethanol,then soaked in magnesium acetate solution of different concentrations and carbonized at different temperatures.Magnesium acetate can produce MgO template,CO₂ and water vapor at high temperature,after the removal of MgO template,mesoporous pores can be left,CO₂ and water vapor can be used as physical activators to produce a large number of micropores.Therefore,all materials had a hierarchical porous structure.The presence of iron impurity in magnesium acetate maked the material have high graphitization degree,and the presence of O and N heteroatoms maked the material have superhydrophilic properties.The optimal sample EMC-2-900 had the highest specific surface area of 1174.2 m² g^-1 and a large total pore volume of 1.57 cm³ g^-1.The high oxygen content and nitrogen content can reach42.29%and 12.26%,which can provide a certain pseudocapacitance.In the three-electrode system and using 1M H₂SO₄ as the electrolyte,the specific capacitance of the EMC-2-900sample was as high as 470.5 F g^-1 at 0.5 A g^-1.Assemblied into symmetrical supercapacitors,when 1M H₂SO₄ was used as electrolyte,the voltage window can reach 1.4 V,and the energy density and power density can reach up to 18 Wh kg^-1 and 175.1 W kg^-1.When 1M Na₂SO₄ was used as electrolyte,the voltage window can reach 2 V,and the energy density and power density can reach 26.1 Wh kg^-1 and 250 W kg^-1.After 10000 galvanostatic charge–discharge cycles at5 A g^-1,the capacitance retention rate was 100%,showing excellent cycle stability.（2）Nitrogen and oxygen co-doped porous carbon SC-n-x was prepared by using N and O rich sea sedge as carbon precursors in the same way.SC-n-x also exhibits high specific surface area and large total pore volume,heteroatomic doping and excellent electrical conductivity.The sample SC-2-800 showed the best physical and electrochemical properties.It had a large specific surface area(1356.8 m² g^-1)and a large total pore volume(2.83 cm³ g^-1),because sea sedge itself had a porous structure,can more fully contact and reaction with magnesium acetate.In the three-electrode system and using 1M H₂SO₄ as the electrolyte,the specific capacitance of the EMC-2-900 sample was as high as 470.5 F g^-1 at 0.5 A g^-1.In the two-electrode system with 1M H₂SO₄ electrolyte,the voltage window can reach 1.3 V,and the specific capacitance obtained was 270 F g^-1,with high energy density and power density of 15.84 Wh kg^-1 and 162.5W kg^-1,respectively.The above two bio-derived porous carbons were successfully prepared and showed excellent physical properties and electrochemical properties,which fully confirmed the feasibility of the method of preparing porous carbon by activating biomass with magnesium acetate.It provided a new idea for the preparation of low cost and high performance electrode materials.