Mild Preparation Process And Electrochemical Properties Of Herbaceous Stem Based Porous Carbon

Electrode material is an important factor affecting the electrochemical performance of supercapacitor.Plant-based porous carbon has become one of the important electrode materials for supercapacitors due to its abundant raw material sources,stable physical,chemical properties,and low cost.Carbonization-activation is the most common and efficient preparation method for plant-based porous carbon,but there are problems such as high cost,high energy consumption,and environmental pollution.It is necessary to explore green and environmentally friendly porous carbon preparation methods.The structure and composition of plants have an important influence on the physical adsorption and electrochemical properties of porous carbon.The herbaceous stem is rich in microtubule tissue and parenchyma cells,and its original tissue cell structure has an important influence on the microstructure of porous carbon.Freeze-drying can retain biological tissues and components,and has potential effects on the pore structure and electrochemical properties of plant-based porous carbon.In this paper,mild processes such as freeze-drying,carbonization,activation,and doping were used to explore methods suitable for the preparation of porous carbon from herbaceous stems,and further develop the preparation theory and electrochemical properties of plant-based porous carbon.Porous carbon was prepared by freeze-drying-carbonization method using peanut sprouts as precursors and peanuts and peanut shells as controls.The feasibility of preparing porous carbon from herbaceous stems by freeze-drying-carbonization method was verified.The effects of freeze-drying on the structure and electrochemical properties of porous carbons generated by precursors with different structures and components were explored.Studies show that the rich heteroatom components of peanut buds can be retained after carbonization to achieve self-doping.The content of N and O atoms on the surface of peanut bud porous carbon obtained by freeze-drying-carbonization method was 5.34 at.%and 12.74 at.%,respectively.However,freeze-drying did not show the expected promotion effect on the electrochemical performance of peanut sprout-based porous carbon.Freeze-drying can greatly retain the characteristic structure of the precursor,but the pore structure and electrochemical properties of porous carbon vary with the different precursors.A method of bean-derived herbaceous stems as precursor body temperature and preparation of N,O co-doped porous carbon was proposed.Nitrogen-rich biomass peanut sprouts were selected as precursors,and the structure and structure of the precursors were maintained by freeze drying.Porous carbon with high heteroatom content was prepared by carbonization-air activation method.The results show that air activation can effectively improve the microporous structure of porous carbon and the content of N and O atoms on the surface,giving porous carbon more pseudocapacitance,which greatly improves the electrochemical performance of porous carbon.The specific capacitance of porous carbon can reach 327 F g-1 at a current density of 1 A g-1.It is expected to further optimize the performance of porous carbon by adjusting the carbonization and activation temperature.An environmentally friendly mild preparation method of celery-based porous carbon was proposed.Nitrogen-doped porous carbon was prepared by baking-activation method using celery stem as precursor,potassium bicarbonate as green activator and urea as nitrogen dopant.Studies show that the combination of freeze-drying and aerobic baking can reduce the amount of activator,and porous carbon with high specific capacitance and high nitrogen doping amount is obtained at a low alkali-carbon ratio.When the baking temperature is 250 ℃ and the alkali-carbon ratio is 1,the prepared porous carbon has the highest specific capacitance.The specific capacitance is 389 F g-1 at a current density of 1 A g-1.The specific capacitance retention rate is as high as 99.1%after 5000 galvanostatic charge-discharge tests at a current density of 5 A g-1,which has excellent cycle stability.