Preparation Of Biomass Derived Carbon Materials And Their Electrochemical Properties

Supercapacitors（SCs）are considered as an ideal energy storage component due to their high power density,long cycle stability,safety and environmental protection,etc.Electrode materials,as a key component affecting their properties,have also been studied more and more.Among many electrode materials,biomass-based materials have attracted more and more attention due to their abundant reserves,good renewability and low cost.It must be admitted thatthe traditional activation process of biomass-based materials can effectively improve their specific surface area,but the carbonized products are often deficient in mesoporous structure and yield.Therefore,it is urgent to find a treatment method of biomass-based materials with low cost,high yield and rich pore structure.In this paper,low cost and a wide range of sources of biomass-based materials as precursors were treated by microwave heating method,and combined with KOH chemical activation,metal CO²⁺catalysis and high temperature annealing process.Three kinds of biomass dervied carbons（BDCs）were synthesized quickly and efficiently with developed pore structure and high capacitance properties,which provides economic feasible strategies for the large-scale production of high-performance biomass porous carbon for SCs.Main contents of this paper are as follows:1.The lotus root starch（LRS）was prepared by microwave heating and hydrothermal heating respectively,and then KOH activated carbonization was used to prepare LRS based BDCs.Raman,XPS,BET and other methods were used to compare the products prepared by the two methods.As opposed to hydrothermal,Microwave heating technology preparation of lotus root starch based biochar（MLRSC）has well developed pores,higher specific surface area(1002.8 m² g^-1),higher oxygen atoms（11.17 at%）.Due to the above advantages of the structure characteristics showed high capacitance performance in the 2.0 mol L^-1 H₂SO₄ electrolyte of three electrode system(under the current density of 0.2 A g^-1 the C_sp as high as 480.2 F g^-1)and good cycle stability(15000 times under constant current charging and discharging cycle in 10.0 A g^-1 has 96.1%capacitance retention).This work provides an efficient method for the preparation of biochar materials with high C_sp,which proves that lotus root starch-based biochar materials have great potential as electrode materials for high-performance SCs.2.The loofah based BDCs was prepared with loofah as precursor by pre-carbonization,KOH activation,CO²⁺catalytic high temperature annealing.Through the synergistic action of KOH activation and CO²⁺catalytic graphitization in the carbonization process,not only the abundant macroporous channel structure in the precursor was retained,but also high specific surface area(1133.8 m² g^-1),large pore volume(0.666 cm³ g^-1),and rich oxygen（15.94 at%）,nitrogen（3.01 at%）atoms content were achieved.It also has excellent capacitance performance(the C_vp of 10.0mg cm^-2loading attains 1188.8 F cm^-3 and the C_sp of 2.0 mg cm^-2loading reaches 653.3F g^-1 at 0.2 A g^-1)and good cycle stability(more than 96%capacitance retention after15,000 constant-current charge and discharge cycles at 10.0 A g^-1).This work provides an economical and feasible synthesis route to prepare of high performance biomass-carbon materials,providing more possibility for the large-scale synthesis of high performance SCs electrode materials.3.The honey-based BDCs was prepared with honey as precursor by microwave and hydrothermal heat treatment,combined with KOH activation and CO²⁺catalytic high temperature annealing.The samples obtained by two heating methods and CO²⁺catalysis（or not）are compared through Raman,XPS,BET etc..The high quality biochar was obtained by microwave treatment,and the three-dimensional interconnected honeycomb CMC has high graphitized structure catalyzed by CO²⁺,as well as large specific surface area(1404.6 m² g^-1),macropore volume(1.081 m³ g^-1),and high oxygen atoms（9.71 at%）.Due to its dominant structural characteristics,SCs based on CMC possess superior capacitive performance,which showed ultra-high capacitance(up to 780.2 F g^-1 at current density of 0.2 A g^-1)and good cyclic stability(97.7%capacitance retention at 10.0 A g^-1 after 15000 cycles)in a three-electrode system of 2.0 mol L^-1 H₂SO₄ electrolyte solution.These results demonstrate that the excellent electrochemical properties of CMC provide an efficient method for the preparation of high heteroatom,high graphitization and superior performance SCs electrode materials,developing an effective strategy for converting biomass materials into functional carbon-based electrode materials for supercapacitors.