Preparation And Performance Of Garlic Skin-Derived Hierarchical Porous Carbon For Supercapacitors

The two major problems facing the sustainable development of society are the shortage of energy and the harsh environment.Energy is the main force driving economic and social development.Fossil energy still occupies a dominant position in various energy forms.With the overexploitation and utilization of fossil fuels,the greenhouse effect has become increasingly severe and environmental pollution has worsened.Therefore,the development of new energy and renewable clean energy is of great significance for human survival and development.Biomass energy is one of the most important renewable energy sources,but it is far from being fully utilized.In recent years,the synthesis of carbon nanomaterials using biomass as a raw material has become an important research direction in the field of carbon nanomaterials.In this paper,porous carbon is prepared by using agricultural waste garlic,which provides an effective way for electrode materials of supercapacitors to be a low-cost,widely-sourced and waste resource utilization.A three-dimensional hierarchical porous carbon is synthesized via a facile chemical activation route with garlic skin as the precursor and KOH as the activating agent.The effects of the impregnation ratio,activation temperature,activation time,carbonization temperature,and carbonization time on the specific surface area and pore volume of porous carbon were investigated by orthogonal experiments.In summary,the optimal synthesis conditions for the garlic skin-derived hierarchical porous carbon(GHC)were determined to be at the impregnation ratio of 4:1 with the activation temperature of 800? for 2.5 h and the carbonization temperature of 600? for 2h.The as-obtained carbon presents a high specific surface area of 2818 m2g-1 and a hierarchical porous architecture containing macroporous frameworks,mesopores(2-4 nm),and micropores(0.6-1.0 nm).The pores are mainly concentrated at 0.4-1 nm,and peaks appear at 0.8 nm.And the formation and evolution mechanisms of hierarchical pores were elucidated.It was discovered that the special structure and composition of the natural materials of garlic peels contribute to the formation of short-range orderly carbon structures and hierarchical porous structures.This structure has great benefits in improving electrochemical performance.In addition,the relationship between the pore size distribution and capacitance was analyzed.It was found that micropores,especially in the 0.4-1.0 nm range,contribute the most to the capacitance.As the electrode material for a supercapacitor,due to its unique interconnected porous structure,this garlic skin-derived carbon exhibits excellent electrochemical performance and cycling stability.At a current density of 0.5 A g-1,the capacitance is up to 427 F g-l(162 F cm-3).Even at a high current density of 50 A g-1,the capacitance can be maintained to a high value of 315 F g-1(120 F cm-3).After charging-discharging at a current density of 4.5 A g-1 for 5000 cycles,the capacitance retention is as high as 94%.Combining the material characterization and pore size distribution,the excellent electrochemical performance is attributed to 3D hierarchical porous structures:(1)Large amounts of micropores provide abun-dant cumulative space for electrons;mesopores shorten the diffusion distance of ions and reduce the diffusion resistance so that ions can easily penetrate into the inner micropores;macropores act as the storage layer for the buffer ions,which are helpful for ion transport.As a result,the porous carbon well balances the specific capacity and the rate performance;(2)The high electrical conductivity reduces the electronic resistance of the device,and the oxygen functional groups ensure good wettability and increase the surface area for ion contact;(3)Short-range orderly carbon structures exist together with hierarchical porous structures.In summary,this paper has studied the preparation process,related characterization and electrochemical performance of garlic peel-based porous carbon.The derived activated carbon has the characteristics of high specific surface area,hierarchical pore size distribution,high specific capacitance,high energy density,high power density,high conductivity,low cost,and simple preparation process.The results show that this garlic peel-derived 3D graded porous carbon is a promising electrode material for high performance supercapacitor.