Preparation Of Waste-based Carbon-based Energy Storage Materials And Study On Their Supercapacitors

As the soul of the supercapacitor,electrode material determines its performance and price.Thus,the exploitation of the high-performance and cost-efficient electrode materials is very important for the development of supercapacitor.Various carbon materials with micro/nano structures,such as graphene,carbon nanotubes,carbon fibers,carbon microspheres,and porous carbons,have been used as high-performance electrode material for supercapacitor due to their high specific surface area,good electrical conductivity,and excellent physical and chemical stability.In this paper,porous carbons,carbon nanotubes and carbon nanotube/metal sulfide composite electrode materials with good supercapacitance performance were prepared by using low-cost waste(waste oil,flax seed residue)as raw material through different methods,such as carbonization-activation process or high-temperature self-pressurization pyrolysis method.The structure and morphology of the obtained materials were systematically characterized,and their supercapacitance performance was systematically tested when using as electrode materials of supercapacitor.(1)A hierarchical porous carbon nanosheet material with high specific surface area and excellent electrochemical performance was obtained through carbonization activation process by using the waste engine oil as carbon source.The effects of carbonization temperature and amount of activator on the morphology,specific surface area,pore volume,surface elements and functional groups of the obtained materials were investigated.The results showed that the obtained material has the highest specific surface area and specific capacitance at the carbonization temperature of 700 °C and the carbon/activator mass ratio of 1:4.The specific surface area of the sample obtained under the optimal condition was up to 2276 m2 g-1,and the pore volume reached 1.19 cm3 g-1.The specific capacitance of the obtained hierarchical porous carbon nanosheet reached up to 352 F g-1 at a current density of 0.5 A g-1,more than 87.7% of initial capacitance is retained as the current density increasing from 0.5 to 20 A g-1,and no apparent capacitance drop is observed after 5000 times charge and discharge cycles.The superior capacitance performance than commercial activated carbon and most of the waste-derived porous carbons,cheap and readily available raw material,and the environmental benefit due to proper recycle of the hazardous waste make the reported hierarchical porous carbon nanosheet become a promising energy storage material.(2)A multi-wall carbon nanotube(CNT)was successfully fabricated through a high temperature self-pressurization pyrolysis method using waste engine oil as carbon source and ferrocene as a catalyst.The results showed that the multi-wall carbon nanotube has the highest purity and the best morphology at the preparation temperature of 900 °C and the carbon source/catalyst mass ratio of 2:1.The specific capacitance of the obtained multi-wall CNT reached up to 75 F g-1 at current density was 0.5 A g-1 when used as an electrode material of supercapacitor,which value was 1.0 time higher than commercial carbon nanotube(38.5 F g-1).When the current density increased from 0.5 A g-1 to 20 A g-1,capacitance retention was about 83.3%,and after 5000 times charge/discharge cycles at 2 A g-1,the specific capacitance was over 95% of the initial specific capacitance,indicating the excellent supercapacitance performance of the obtained multi-wall carbon nanotube.(3)A CNT/Fe S2 composite was prepared by using waste engine oil as carbon source,ferrocene as a catalyst and iron source,and sublimed sulfur as sulfur source through a high temperature self-pressurization pyrolysis under appropriate condition.The residual nano iron particles in the preparation of carbon nanotube were fully utilized to fabricate a CNT/Fe S2 composite for avoiding the waste the iron particles and simplifying the preparation process.The obtained composite were systematically characterized and its supercapacitance performance was investigated.A 3D network morphology was obtained by attaching nano Fe S2 on the surface of CNT or coating nano Fe S2 into CNTs.When using the composites as electrode material of supercapacitor,the specific capacitance of the obtained composite reached up to 350 F g-1 at a current density of 0.5 A g-1,which value was about 1.45 times higher than that of the pure nano Fe S2.When the current increased to 10 A g-1,the capacitance retention rate was ca 56.4%,while the capacitance retention of the pure nano-Fe S2 was only 21%.Meanwhile,the capacity retention of the composite after 1000 charge/discharge cycles was about 1.5 times higher than that of nano-Fe S2,which was significantly increased from 46.5% to 69.7%.(4)A hierarchical porous carbon material with high specific surface area and excellent electrochemical performance was obtained by using flax seed residue as a carbon source through a carbonized activation process.The optimized sample had a specific surface area of up to 3230 m2 g-1 and a pore volume of 1.67 cm3 g-1.The specific capacitance of the obtained hierarchical porous carbon reached up to 369 F g-1 at current density was 0.5 A g-1,and when the current density increases to 20 A g-1,the specific capacitance still reached to 92.7% of the initial capacitance.Over 98% of the initial capacitance can obtain after 5000 times charge/discharge cycles at current 2 A g-1,indicating the excellent rate and cycle performance of the obtained hierarchical porous carbon.