Preparation Of Biomass Porous Carbon Nanomaterials And Its Application In Supercapacitors

With the speedy development of electronic technology,the requirement of electric energy increases rapidly.Meanwhile,the energy consumption and environmental pollution become the major challenges for the whole world.Therefore,it is pressing demands to research and develop the sustainable renewable energy and corresponding device of energy storage and conversion,for which the supercapacitors come into existence as the situation requires.Supercapacitor is a green,efficient,unique and new-type energy storage unit with the performance between rechargeable battery and common capacitor.It has ultra-high power density,instantaneous charge/discharge,long cycle life and a wide range of operating temperatures.Electrode material is a key factor to determine the electrochemical energy storage performance of supercapacitors.Therefore,researchers pay more attention into the design and synthesis of the correlative materials.Currently,porous carbon nanomaterials derived from biomass have become a research hotspot in this field due to their unique microscopic morphology,large specific surface area,abundant porous structure and excellent electrical conductivity.The purpose of this study is to fabricate three-dimensional porous carbon nanomaterials with unique morphology and performance by means of physical and chemical methods,in which abundant,inexpensive and natural renewable biomass,such as green baby jade,clematis tangutica and prickly ash seed,is used as carbon precursor.Furthermore,the as-prepared materials are used to assemble asymmetricor symmetrical supercapacitors in order to investigate electrochemical storage energy of the materials and evaluate their application value.The main research contents are as follows:1.The three-dimensional porous carbon materials crosslinked with each other?BJAC?were successfully prepared by using the baby jade as the carbon source and KOH as activator respectively,in which the baby jade is pretreated by means of the freeze-drying technology to keep its original microstructure.When the mass ratio of baby jade/KOH was equal to 3:1,the as-obtained BJAC-3:1 had an ultra-large specific surface area of 2429.5 m²g^-1,a pore volume of 1.605 cm³g^-1,an average pore diameter of 2.64 nm,and a high pore volume of 92.3%.Under the three-electrode system,the specific capacitance of BJAC-3:1 electrodes is up to 273 F g^-11 at 1 A g^-11 in the 6 mol L^-1KOH,and it can still be maintained 84.61%of initial value at 100 A g^-1.The energy density of symmetrical supercapacitor?BJAC-3:1//BJAC-3:1?constructed with BJAC-3:1 is as high as 13.8 Wh kg^-1(at power density 0.7 KW kg^-1).2.Porous carbon tube bundle?CNT?electrode material was successfully designed through hydrothermal treatment,carbonation and KOH activation by using Clematis tangutica as precursor.Furthermore,the specific surface area and pore size distribution of the material were adjusted by controlling the hydrothermal conditions,carbonization temperature and the amount of activator.Thanks to the hollow tubular morphology and porous structure of the prepared carbon material,the transportion of electrons along the tube wall and the diffusion of ions in the carbon tube are promoted with small resistance,thus,the material exhibits excellent electrochemical performance.The specific capacitance of electrodes is up to 328 F g^-11 at 1 A g^-11 in 1mol L^-1H₂SO₄ electrolyte.After 5000 cycles of charge and discharge,the specific capacitance only decreases 8.1%.The energy density of the symmetrical capacitor?CNT-800-1:3//CNT-800-1:3?can reach 12.44 Wh kg^-1(with power density of 700 W kg^-1).3.Biomass carbon materials?BAC?with hierarchically porous graphene-like nanosheets were prepared by using prickly ash seed as raw material,and following by an activation of grinding solid KOH and pyrolysis in inert atmosphere.Subsequently,the AAQ-BAC and DCNQ-BAC electrode materials were synthesized by using the BAC as conductive substance with adsorbing 1-amino anthraquinone?AAQ?and2,3-two-1,4-naphthalene quinone?DCNQ?via non-covalent functionalization.The AAQ-BAC is used as a positive electrode and DCNQ-BAC as the negative electrode respectively,an asymmetric capacitor?DCNQ-BAC//AAQ-BAC?was assembled.The energy density of the device is as high as 16.2 Wh kg^-1(the power density is 900W kg^-1)under the working voltage of 1.8 V.