Preparation And Capacitive Performance Of Biomass-derived Porous Carbon

Recently,the fast development of portable electronic products has stimulated domestic and foreign scholars interested in new-type energy storage devices.Among various energy storage devices,solid-state supercapacitors（SSCs）have received worldwide attention from researchers by their relatively high power density,rapid charge/discharge,long service life,and eco-friendliness.In this work,a series of biowastes derived porous carbon materials were prepared by employing abundant biowastes（soybean dregs and cotton stalks）as carbon sources and potassium hydroxide（KOH）as activator.Meanwhile,the morphology,structure,composition and electrochemical performance of as-obtained carbon materials were explored in detail by the combination of various characterizations and electrochemical techniques.The main conclutions of this thesis are as follows:At first,we introduce an efficient strategy by using soybean dreg as carbon source to prepare N/O dual-doped porous carbon frameworks by hydrothermal and pyrolysis/activation methods for the first application in quasi-solid-state supercapacitors（QSSC）devices.The research shows:the employed method efficiently alleviates the restacking of carbon sheets and can well regulates their textural properties and electroactivity to realize outstanding performance.By controlling the pyrolysis temperature,a structure-optimized porous carbon material（H-SDC-A650）is obtained.This carbon shows ultrahigh capacitance and excellent rate performance in both three-electrode cell and two-electrode cell.Significantly,the H-SDC-A650 based QSSC achieves integrated high energy and power densities of 9.3 Wh kg^-1 and 9883 W kg^-1.This device can also work well for powering small electronics.H-SDC-A650 shows a stronger competitiveness.This study not only widens the path for preparing carbon-based materials,but also brings new idea for device development.At second,we introduce an efficient strategy to prepare carbon（HSC-0.50）with tuned porosity,high surface area,and relatively high packing density by using the alkaline-assisted hydrolysis of SDs and pyrolysis for high-energy device applications.It can be found that HSC-0.50 presents high gravimetric and volumetric capacitance of 281.4 F g^-1 and 247.6 F cm^-3 at 0.5 A g^-1,and superior rate capability of 83.2%retention at a large rate of 100 A g^-1.Under high mass loading of 20 mg cm^-2,high volumetric and areal capacitances of 204.7 F cm^-33 and 4.7 F cm^-22 are also delivered by HSC-0.50.HSC-0.50-based QSSCs using alkaline（PVA/KOH）and neural（CMC-Na/Na₂SO₄）electrolyte gels are subsequently constructed for electrochemical evaluation.Owing to significantly extended voltage window（1.8 V）in neural case,neural device allows a superhigh energy density(23.4 Wh kg^-1),greatly exceeding that of alkaline device(7.6 Wh kg^-1).Accordingly,inexpensive and sustainable biowaste-derived carbons（particularly from the SDs）is highly appealing for use in high-performance energy storage.At third,we introduce a self-doped carbon nanofoam（A-CS650）through a facile method using Xinjiang’s naturally abundant crop biowaste—cotton stalks as carbon source.A-CS650 demonstrates exceptional performance contributed by synergistic features of large surface area,hierarchical porosity and rich defects.A-CS650 presents gravimetric and volumetric capacitances up to 282 F g^–1 and 234F cm^–3 at 0.5 A g^–1,and a high-rate capacitance retention of 72.7%at a large rate of100 A g^–1.With increasing the mass loading to 20 mg cm^–2,A-CS650 still retains good performance.Especially,by using CMC-Na/Na₂SO₄ gel electrolyte,as-constructed 1.8 V QSSC displays an outstanding energy density(22.6 Wh kg^–1),greatly exceeding the value in PVA/KOH electrolyte(7.3 Wh kg^–1).Besides,this device exhibits considerable stability over 10000 cycles（81.6%capacitance retention）.This work verifies that cotton stalk-based porous carbon will have broard application in supercapacitors.