Preparation And Electrochemical Properties Of Porous Carbon Material

The continuous consumption of non-renewable energy(coal,oil,natural gas,etc.)has caused serious environmental problems and restricted economic development,while the clean energy such as solar,wind,water and tidal is intermittent and cannot be transformed into electric energy in a long-term and stable way.Therefore,it is urgent to develop efficient energy storage devices to achieve sustainable renewable energy.Among them,supercapacitors are widely used in virtue of their versatile advantages including high power density,rapid charge/discharge property and long cycle life.Organic dyes containing heteroatoms in industrial wastewater are potential electrode materials for supercapacitors.And the waste biomass itself possesses a three-dimensional carbon skeleton,which can be combined with other carbon nanomaterials to obtain high-performance electrode materials.Based on this,methylene blue(MB)and spent coffee grounds(CGs)were selected to prepare porous carbon electrode materials,and applied in the supercapacitor to achieve energy storage and conversion.(1)In this work,nitrogen and sulfur co-doped porous carbon material(A-MBCP)was successfully prepared from MB in wastewater by facile one-step carbonization and activation method.A-MBCP possesses large specific surface area(SSA)of 560.0 m2 g-1,high content of N,S in-situ doping and large interlayer spacing.The prepared A-MBCP electrode reaches specific capacitance of 302.0 F g-1 at 0.5 A g-1.Furthermore,the assembled A-MBCP-based supercapacitor displays energy density of 25.0 Wh kg-1 at power density of 800.0 W kg-1,however,its capacitance retention is relatively low due to the few macropores in A-MBCP.Meanwhile,the high capacitance retention of 98.6%and coulombic efficiency of 97.9%are achieved for the supercapacitor after 3000 cycles,implying its favorable long-term charge/discharge stability and reversibility.This work presents a new perspective of using MB as precursor of electrode material,and provides theoretical guidance for the application of MB or other dye waste in the supercapacitors field.(2)On this basis,the multi-dimensional hierarchical porous carbon was constructed by self-assembly method,and its practical properties,such as areal and volumetric capacitance,were characterized to further evaluate the electrochemical properties of electrode materials.CGs as carbon source was mixed with graphene nanosheet(GNS)and carbon nanotube(CNT)to prepare the multi-dimensional hierarchical porous carbon composite(CGCM@GNS&CNT).CGs with abundant macroscopic pores was utilized as 3D carbon skeleton and the GNS&CNT anchored on them was applied to enhance the physical and electrochemical properties.The composite material exhibits defined hierarchical porous structure,high SSA of 460.0 m2 g-1,interconnected conductive network and abundant heteroatom(O and N).Furthermore,the CGCM@GNS&CNT electrode achieves a areal capacitance of 441.0 mF cm-2 and volumetric capacitance of 90.0 F cm-3 at 1.0 mA cm-2.More importantly,the CGCM@GNS&CNT-based supercapacitor shows an excellent rate property,realizing the quick charging ability of the supercapacitor.And it affords a remarkable energy density of 31.0 μWh cm-2 at a power density of 800.0 μW cm-2.The capacitance retention and coulombic efficiency can retain 102.5%and 100.5%over 2000 cycles,respectively.This work provides an important idea for the development of environment-friendly porous carbon electrode materials and promotes the development of multi-dimensional hierarchical porous carbon in the field of energy storage.