Study On Synthesis Of Hierarchical Porous Carbon Derived Biochar And Its Eletrochemical Capacitors In Both Acidic And Alkalic Electrolytes

Electrochemical capacitors(ECs),also known as supercapacitors,have been widely applied as driving powers for high-power electronic devices,digital devices,and so on due to their characteristic of outstanding power density(Pd),long cycling stability,environmental friendliness and fast charge/discharge,electrical sources.Compared with batteries,ECs usually suffer from low energy density(Ed,around 5 W h kg-1),which greatly hampers their potential commercial applications.ECs devices with large Ed can be assembled through developing and constructing new functional porous carbon materials and choicing electrolytes to march with them(the match between the electrode materials and electrolytes includes the match between the pore size of electrode material and the electrolyte ion size,between electrolyte conductivity and wettability of electrode material,between the pseudocapacitance and the functional electrode material,and between the pseudocapacitance and the nature of the used electrolyte,and so on).Acid and alkali electrolytes are commonly used as the electrolyte solutions of ECs due to their low cost,safety and reliability,environmental friendliness,high conductivity and the properties of the pseudocapacitive effects inducing by the easy interaction between the acidity and basicity of the electrolytes and the surface functional groups of the carbon.The traditional synthesis of carbon materials commonly use non-renewable resources such as oil and coal as raw materials,the preparation process is complex and sometimes involve the toxic chemical reagents.Therefore,there is an urgent to design advanced carbon via a route with low cost,renewable resources as raw materials.Biomass has attracted more and more attention in the materials of ECs in recent years.Biomass-based is natural renewable resource,features uniform porosity and in-situ heteroatom doping(N,O,B,S,P,etc.)and optimal hierarchical structure with naturally perfect interconnection.This is not only provide high accessible surface area,facilitate rapid ion transport by supplying ion-buffering reservoirs and ion-transport pathways,but also provide an additional pseudocapacitance from the redox reaction occurring on the heteroatom surface,wettability,which ensure high Ed.In this paper,the advanced porous carbon materials were prepared by using agricultural and forestry waste biomass as carbon sources,and ECs devices were assembled with the as-prepared carbons.The main research works are as follows:1.High performance ECs electrode materials with three dimensionally interconnected carbon nanorings are prepared from batatas stalks and leaves(BSL)through facile carbonization followed by a KOH activation process.The pore structure,surface area and surface elements of the capacitive carbon can been controlled through adjusting the activation ratio and the pyrolysis temperature.The BSL-KC-1:4-700 matches well with acidic and alkalic electrolytesand exhibits high electrochemical performance: in 1 mol L-1 H2SO4 aqueous electrolyte,its specific capacitance of 532.5 F g-1 and 264.0 F g-1 with capacitance retention 95.1%(1000 cycles)and 91.7%(10,000 cycles)after at 1 A g-1 and at 30 A g-1 current density,respectively,and high Ed of 25.8 Wh kg-1 with Pd of 13068.0 W kg-1;In 6 mol L-1 KOH electrolyte,its specific capacitance of 350.0 F g-1(1 A g-1)with 95.06% and 91.1% of capacitance retention after 1000(1A g-1)and 10,000(30 A g-1)cycles,respectively,high Ed 24.5W h kg-1 and Pd 12918.0 W kg-1.Therefore,our work not only describes a low-cost,environmental friendliness and facile preparation method to produce a carbon electrode material for high-performance supercapacitors in strongly alkaline/acidic environments,but also inspires a promising and potential application in energy conversion devices.2.CCVS-derived hierarchical porous 3D structured carbons with tunable porosity(temperature and activation ratio)and enhanced electrochemical performance is prepared via carbonization combined with KOH activation.The as-prepared CCVSK4-700 exhibits higher BET area(2675.3 m2 g-1)and higher specific capacitance(555 F g-1).3.Hierarchical pore interconnected structures of 3D carbon with 3156.4 m2 g-1 high specific surface areas,1.45 cm2 g-1 pore volume and heteroatom doping are successfully prepared via simple carbonization and KOH activation of Flower of Trachycarpusfortunei(Hook.)H.Wendl(FTHW).In 1 mol L-1 H2SO4 electrolyte,the as-prepared FTHWK4-700-based electrode materials exhibit 562 F g-1 specific capacitance at 1 A g-1,high Pd 9703.4 W kg-1 and Ed 29.3 W h kg-1.Moreover,the assembled ECs in 6 mol L-1 KOH aqueous electrolyte exhibits a 415 F g-1 specific capacitance at 1 A g-1.