Preparation And Supercapacitive Performance Of Folic Acid-based N/B/O Co-doped Porous Carbon Materials

Nowadays,supercapacitors have gradually become a research hotspot due to their high power density,excellent cycle stability and wide operating temperature range,but their electrochemical performance is largely dependent on electrode materials.Therefore,the development of electrode materials with excellent performance has become the basis for the research and development of high-performance supercapacitors.Porous carbon materials have been widely used as electrode materials for supercapacitors due to their unique properties such as abundant sources,easy modifiability,good stability,and large specific surface area.However,pure porous carbon materials tend to have poor capacitive performance.Heteroatom（such as N,O,B,S,etc.）doping is an effective capacitance enhancement strategy,which can introduce various functional groups that can undergo Faradaic reaction in carbon matrix to improve the specific capacitance as well as the surface wettability of porous carbon materials,hence,the electrochemical performance of supercapacitors can be improved.In this thesis,organic small molecule folic acid with high N/O content is used as the C/N/O precursor,and the research on how to easily and efficiently prepare heteroatom-doped porous carbon materials with high capacitance performance is carried out.The prepared materials are used as electrode materials for supercapacitors,and the reasons for the high capacitive of the materials are analyzed by combining their structures and compositions.The specific research contents of this thesis are shown as follows:（1）Preparation and supercapacitive performance of N/B/O co-doped porous carbon nanoparticles.In the present study,the N/B/O co-doped porous carbon nanoparticles are fabricated by the carbonization of pre-mixed precursors consisting of ammonium folate,boric acid,and ammonium phosphate,in which ammonium folate,boric acid,and ammonium phosphate served as C/N/O source,B dopant,and activating agent,respectively.Owing to the large specific surface area(1400 m²g^-1),optimal porosity distribution,and high heteroatom contents（N,9.62 at%;B,1.47 at%;and O,14.12 at%）,NBCP-850 electrode shows a high capacitance of 447.3 F g^-1at0.5 A g^-1in alkaline electrolyte.Symmetrical supercapacitors assembled with NBC-850 electrodes deliver energy densities of 13.67 Wh kg^-1and 32.61 Wh kg^-1,respectively,in KOH and Na₂SO₄electrolytes.In addition,an imidazolium-based gel polymer electrolyte（MPEI-TF-IL）is prepared by Debus-Radziszewski reaction using polyethyleneimine（PEI）,glyoxal and formaldehyde as starting materials.The MPEI-TF-IL gel polymer electrolyte exhibits a high ionic conductivity(28.1 mS cm^-1at 25℃)and a wide electrochemical stability window（2.8 V）.Flexible solid state supercapacitor（FSSC）fabricated with NBCP-850 electrode and MPEI-TF-IL electrolyte can deliver a large energy density of 57.5 Wh kg^–1at 357.7 W kg^–1,showing its promising potential in powering flexible and wearable electronics.（2）Preparation and supercapacitive performance of N/B/O co-doped layered porous carbon materials.N/B/O-codoped layered porous carbon materials have been successfully fabricated via simply annealing a mixture of ammonium folate,gelatin,and boric acid.In this synthesis,ammonium folate and gelatin served as the carbon precursor with N/O source,while boric acid served as B dopant.The N/B/O co-doped layered porous carbon material（NBCL-850）prepared under the optimal conditions has large specific surface area(1822 m²g^-1,in which the micropore area accounts for51.4%),high heteroatom contents（N,12.28 at%;B,5.68 at%;O,13.14 at%）and layered structure.Owing to these merits,the NBCL-850 electrode exhibits a high specific capacitance of 523 F g^-1and 525.2 F g^-1in acidic and alkaline electrolytes,respectively,at a current density of 0.5 A g^-1.In addition,the NBCL-850-based supercapacitors exhibited the energy densities of 14.72 and 35.42 Wh kg^-1together with the cycling stabilities of 92.1%and 98.3%capacitance retentions after 10,000charging/discharging cycles,respectively,in 6 M KOH and 1 M Na₂SO₄electrolytes.FSSC fabricated with NBCL-850 electrode and MPEI-TF-IL electrolyte exhibits a high energy density of 69.6 Wh kg^–1and a high capacitance retention of 79.3%,showing its promising potential in powering flexible and wearable electronics.