Preparation,Modification And Application Of Biochar Derived From Kapok Fibers

With the progress of science and technology,and development of society,energy need has became greater and greater,which aggravates the crisis of energy resource and environmental pollution problem.Supercapacitor,as a new type of power storage equipment,fits in with the demands for energy,and receives more attentions.Performances of supercapacitor mainly depend on electrode material and electrolyte.So it is important to prepare good electrode material and choose suitable electrolyte.Biochar possesses advantages of large specific surface area and abundant pore structures.Especially,biochar derived from kapok fibers with unique tube structure and 2D layers is the one of greatly potential electrode materials.For the biochar derived from kapok fiber as electrode material,choosing suitable electrolyte,especially redox electrolyte,is of great significance to improve its electrochemical performance.In this thesis,to enhance electrochemical performances of biochars,biochars derived from kapok fibers were prepared by adjusting preparation conditions,and a new electrolyte was chosen.The details are as follows:（1）Biochars at different pyrolysis temperatures were obtained by one-step pyrolysis method and they were further used as supercapacitor electrode materials.The results showed that the biochar C_KF-750 obtained at pyrolysis temperature of 750 ℃ had numerous micropores and mesopores,and its specific surface area was 1125.7m2/g.At a current density of 1 A/g,the specific capacitance of C_KF-750 was 283 F/g.After 10000 charge-discharge cycles,specific capacitance kept almost same.（2）By using two-step method,activation process with KOH as activator was carried out to prepare 2D biochar nanosheets.Influence of alkali content on structure and performance of the2D biochar nanosheets was investigated after adjusting alkali-carbon ratio.The results showed that KOH had the ability to destroy the layer structure of kapok fiber and nanosheets were obtained.When the alkali-carbon ratio was 5:1,2D biocar nanosheets AC_KF-5 derived from kapok fiber possessed superhigh specific surface area（3359.2 m2/g）and large pore volum（2.1415 m3/g）.At a current density of 1 A/g,the specific capacitance of AC_KF-5 was 405 F/g.Its rate capacity and cycling stability were also wonderful.（3）New-type redox electrolyte was prepared with 1 mol/L H2SO4 as solvent and potassium ferricyanide and potassium ferrocyanide as redox additives.Ratio of the two additives was adjusted to study the influence of additive ratio on the electrochemical performance of AC_KF-5.The results indicated that when the ratio of potassium ferricyanide and potassium ferrocyanide was 2:1,AC_KF-5 presented a specific capacitance of 3380 F/g at a current density of 10 A/g.Even when the current density increased to 30 A/g,its specific capacitance still reached up to 1170 F/g.Symmetrical supercapacitor consisted of the new-type redox electrolyte and AC_KF-5 possessed high energy density of 264.1Wh/kg.