Preparation Of Waste Biomass Based Porous Carbon Materials And Its Application In Supercapacitors

Biomass derived carbon materials have attracted extensive attentions in the fields of supercapacitors,lithium-ion batteries,adsorption and catalysis etc.because of their numerous advantages,such as low cost,abundant,renewable raw materials,environmentally friendly,adjustable pore size distribution and rich in heteroatoms.Waste biomass,such as pomelo peel and litchi shell,contains 3D pore structure,shows a great potential as biomass carbon source.In this dissertation,the preparation and modification of biomass carbon electrode materials for supercapacitores were studied.Two kinds of activated biomass carbon materials,litchi shell carbon and pomelo peel carbon,were designed and synthesized.Doping modification and compositing modification strategies were developed to improve the electrochemical performance of the synthesized activated biomass carbons.The main results obtained in this dissertation are as follows:（1）Porous carbon produced from lycheee shell and its supercapacitor performance:Porous activated carbon material was prepared by a simple and low-cost KOH activation process using waste litchi shell as carbon source.The electrochemical characterization results show that the specific capacitance of the activated litchi shell carbon material is as high as 222.0 F/g at the current density of 0.1 A/g.The maximum power density and energy density of the assembled symmetrical capacitor are 35950W/kg and 17.6 Wh/kg respectively.The Peukert factor K value is 1.02,indicating that the symmetrical capacitor assembled with the prepared activated litchi shell carbon material has an excellent rate performance.Such good electrochemical performance is attributed to the large surface area,high pore volume and wide average pore diameter of the prepared activated litchi shell carbon material.This work provides a new strategy to prepare two-dimensional carbon materials for energy conversion and storage.（2）Heteroatom-doping of litchi shell-based carbon and its application in supercapacitor:On the basis of activated litchi shell carbon,heteroatoms co-doping strategy with thiourea as both sulfur and nitrogen source to improve the electrochemical performance of biomass carbonlitchi was developed..The results show that the specific capacitance of the modified shell carbon is 238.4 F/g at the current density of 0.1 A/g.The specific capacitance of the assembled symmetrical supercapacitor with 1 mol/L sodium sulfate and ionic liquid electrolyte are 58.8 and 52.7 F/g,respectively.Impedance results show that the time constant of the supercapacitor with 1 mol/L sodium sulfate as electrolyte is only 0.33s,indicating a superfast capacitance characteristic and a considerable application potential.Such a good capacitance behavior can be attributed to the high specific surface area,low micropore ratio,wide average pore diameter and relatively high S,N doping contentsl of the modified active litchi shell carbon material.（3）Preparation of Mn O-litchi shell carbon composite and its application in supercapacitor:The porous litchi shell carbon-Mn O nanoflower composite was prepared by a one-step activation method with the waste biomass litchi shell as carbon source,KOH and KMn O₄as co-activate agent.The composite could be used as both of anode material and cathode material for supercapacitors,with specific capacitances of551.8 F/g and 795.5 F/g at the current density of 0.5 A/g,respectively.And the corresponding electrochemical conversion are Mn（II）?Mn（III）and Mn（III）?Mn（IV）,respectively.A hybrid symmetric supercapacitor was assembled with the prepared composite material as both anode and cathode materials,showing a very good rate performance and cycle stability.This work provides a simple method for the preparation of carbon/metal oxide composite materials,offering a new idea for the design of new hybrid symmetric supercapacitors.（4）Three-dimensional porous carbon produced from oxygen-rich pomelo peel and its supercapacitor performance:Porous oxygen-doped carbon was synthesized from the pomelo peel by a two-step low-cost carbonization-KOH activation process.After this process,oxygen functional groups were introduced into the material,which acted as hydrophilic groups.Results show that the oxygen doped pomelo peel carbon material has a super high specific surface area of 2378.1 m²/g and a large pore volume of 1.13cm³/g.A high specific capacitance of 292 F/g can be obtained at a current density of 0.5A/g.Besides,the capacitance retention rate can reach 96.41%in 1000 cycles at a current density of 1 A/g.The excellent electrochemical performance of oxygen doped pomelo peel carbon materials is due to its three-dimensional porous structure and the abundant oxygen functional groups,which provides channels for electrolytes and improves the hydrophilicity of the material.（5）Preparation of MoS₂-activated pomelo peel carbon composite and its application in supercapacitor:The activated pomelo peel carbon was loaded with MoS₂nanosheets by hydrothermal method.The specific capacitance of the composites material is 1093.2 F/g at the current density of 0.1 A/g,which is much higher than that of the unmodified pomelo peel carbon sample.When using the pre-mentioned litchi shell carbon-Mn O composite as negative electrode and using the pomelo peel carbon/MoS₂composite as positive electrode,the prepared device showed a specific capacitance as high as 161.3 F/g at the current density of 0.1 A/g.The highest energy density and power density are 50.2 Wh/kg and 8600 W/kg,respectively.The impedance results show that the time constant of the supercapacitor is only 0.32 s,which shows a superfast capacitance characteristic and a high application potential.