Research On Preparation And Electrochemical Properties Of Biomass-based Activated Carbon

As a new type of energy storage device with broad application prospects,the key of supercapacitor research is the research of electrode material.Biomass materials have a wide range of sources,are easy to obtain and low in price.The activated carbon（AC）prepared from biomass has a natural porous structure,good wettability and high conductivity.At present,the preparation of electrode materials for supercapacitors from biomass has attracted extensive attention of researchers.In this thesis,different raw materials were used as precursors,and different methods were applied to prepare activated carbon materials.The following conclusions are obtained:（1）AC was prepared with buckwheat husk as raw material and KOH as activator.The surface morphology,porosity and electrochemical characteristics of activated carbon were studied.The results showed that the iodine adsorption value,specific surface area and specific capacitance of activated carbon increased with the increase of alkali-carbon ratio.The average pore diameter of activated carbon prepared at an alkali carbon ratio of 5:1 was 2.10 nm,the specific capacitance was 295 F g^-1 when the potential scanning speed was 2 m V s^-1,and the specific surface area utilization rate reached 63%of the theoretical value.When the power density was increased by 30 times,the energy density retention rate could reach 70.5%,which showed excellent electric double-layer capacitance characteristics.（2）The buckwheat husk was frozen before using,the effects of freezing and alkali-carbon ratio on buckwheat husk-based activated carbon were investigated.It was found that the proportion of microporous pores in buckwheat husk carbide after freezing increased by 11%,indicatde that freezing was conducive to the generation of micropores in buckwheat husk.After freezing treatment,the utilization rate of the specific surface area of activated carbon prepared with an alkali-carbon ratio of 4∶1 reached 65.5%of the theoretical value,and the specific capacitance was as high as 338 F g^-1.Compared to unfrozen buckwheat husk-based activated carbon,the specific capacitance of activated carbon prepared by freezing increased by 14%,and the amount of activator decreased by 20%.When the power density was increased by 30times,the capacitor energy density retention rate could reach 70.6%.The results showed that the preparation of activated carbon by freezing method not only reduced the preparation cost,but also improved the capacitive properties of the electrode material.（3）The preparation process of active carbon from frozen sawdust by chemical activation method,and the AC was studied as electrode material for supercapacitor.The results showed that the pores of activated carbon prepared from frozen sawdust were mainly micropores,which had the characteristics of high specific surface area of biomass based activated carbon,and good electrochemical properties.The surface area of activated carbon prepared with an alkali carbon ratio of 4:1 was 2878 m² g^-1,and the specific capacitance was 353 F g^-1 at a potential scanning speed of 2 m V s^-1.When the scanning speed was increased to 50 m V s^-1,the specific capacitance retention rate reached 75%.（4）Frozen okara was used as precursor,the mass ratio of activator to precursor was changed to adjust the pore structure of AC,material characterization and electrochemical tests were carried out on a series of activated carbons.The experimental results showed that the electrode material prepared from frozen okara had good electrical conductivity.The surface area of activated carbon prepared with an alkali carbon ratio of 5:1 was 3473 m² g^-1,and its average pore size was 2.45 nm.The electrode had a specific capacitance of 364 F g^-1 when its scanning speed was 2 m V s^-1.When the scanning speed was increased by 25 times,its specific capacitance retention rate was 61.2%.