The Green Preparation Of Hierarchically Porous Carbon From Waste Precursors And Its Energy Storage

Hierarchically porous carbon?HPC?with interconnecting micropores,mesopores and macropores is used widely as the supercapacitor and lithium ion battery?LIB?electrodes.The traditional synthesis of HPC includes template method or chemical activation method.However,some problems involve in above process including fussy procedure,equipment corrosion and serious pollution.In this thesis,serials of HPC have been prepared using intrinsic CaCO₃ of biomass as the self-template or/and the self-activation agent.The electrochemical properties of HPCs as the electrode materials for supercapacitors and LIBs were investigated in detail.The main results are listed as follows:Nitrogen-doped carbon materials with abundant micropores,mesopores and macropores were prepared from shrimp shell using its intrinsic mineral scaffold?CaCO₃?as the self-template,chitin as the carbon and nitrogen sources combined with ZnCl₂ activation.The specific surface area of the obtained carbon materials ranging from 638 to 1170 m² g^-1 can be facilely controlled via adjusting the activation temperature,the mass ratio of shrimp shell to ZnCl₂ and template removal sequence.And the nitrogen content ranging from 6.3⁸.1 wt.%can be tailored after pyrolysis of shrimp shell,which favors the final electrochemical property.The HPC named as C/ZC-700-1 pyrolyzed at 700 ^oC shows the largest specific surface area of 1170 m² g^-1and the suitable nitrogen content of 7.2 wt.%in all the obtained carbons.The as-prepared HPC exhibits high electrochemical performance when used as the supercapacitor electrodes.Among them,C/ZC-700-1 sample displays the largest specific capacitance of 318 F g^-1 at a current density of 0.1 A g^-1 in a 6 M KOH electrolyte and the best cycle stability with 95.6%retention(261 F g^-1 at a current density of 1.0 A g^-1)after 10000 cycles.Its specific energy density and power density are 6 Wh kg^-1 and 995 W kg^-1 in two-electrode cell,respectively.The high electrochemical performance can be attributed to the synergistic effect of the double layer capacitance formed by the hierarchical pores and the pseudocapacitance formed by the nitrogen doping nature.A new strategy for the synthesis of 2D sheet-like HPC with soft pitch as the carbon source and oyster shells as both the template and activation agent was reported.The confined space of sheet-like CaCO₃ in oyster shells provides the chance for soft pitch diffusion and penetration of in-built template,and the obtained carbon derived from pyrolyzed pitch inherits its sheet morphology of mother template to produce 2D carbon sheets.Furthermore,interconnected micro-,meso-and macroporous carbon networks can be fabricated with CaO as the self-activation agent,which was formed from the decomposition of biological CaCO₃.The specific surface area and pore size distribution of the obtained HPC can be simply tuned respectively from 612 to 1258m² g^-1 and 0.7 to 9.5 nm by varying the pyrolysis time and the mass ratio of soft pitch to oyster shells.When used as the electrode material of LIB,the typical HPC material with the specific surface area of 920 m² g^-1 and the pore size of 0.7⁶.5 nm exhibits the highest reversible capacity of 1251 mA h g^-1 at a current density of 0.1 A g^-1 with excellent cycle stability(94%capacity retention after 450 cycles at 1.0 A g^-1)and rate capability.These exciting results indicate that the 2D layered HPC can effectively limit the volume expansion of the LIB during charging and discharging process,and the interconnected porous structure is beneficial to the improvement of the capacitance.