Preparation And Electrochemical Performance Of Molten Salt Activated Loofah Carbon And Loofah-Based Composites

In order to meet the increasing demands of electrochemical energy conversion and storage-related applications,and to meet the requirements of sustainable development and an environmentally friendly society,the development of supercapacitors with high electrochemical performance is an urgent need.And carbon materials are the core of energy storage and conversion.Therefore,the demand for them has grown steadily.In order to meet this demand and not have a major impact on the environment,biomass materials that have been widely existing in nature have entered the field of vision of researchers.In order to transform biomass into carbon materials with excellent performance,the academic generally use potassium hydroxide and other strong corrosives that have strong damage to the environment,equipment and labor.In this case,the molten salt activation method as a green treatment method has become a more eco-friendly choice.In this paper,loofah which is widely planted in our country,has a low cost,and has a rich original pore structure is selected as the biomass carbon source,and green and sustainable molten salt treatment is used to treat it.In addition,the nature pore structure of loofah is an ideal carbon framework,and the composite of transition metal oxide nanomaterials on its surface is expected to improve the stacking problem of redox nanomaterials and poor rate performance.The main contents are as follows:(1)Loofah carbon is obtained by carbonizing the loofah at high temperature.The common potassium hydroxide chemical activation method is replaced by the molten salt method,and the loofah carbon and Na Cl/KCl mixed salt are uniformly mixed in different mass ratios to prepare the molten salt method to activate the loofah carbon(denoted as SAC)material.By changing the carbon/salt mass ratio,it is found that at a current density of 1 A/g,the SAC-1:5 electrode material with a carbon/salt ratio of 1:5 has a specific capacitance of196 F/g,which is higher than the commonly KOH activated loofah carbon material(denoted as KAC,188 F/g).The study also found that the presence of molten salt significantly improves the rate performance of the material.SAC-1:5 has a capacitance retention rate of nearly 80%at a large current density of 30 A/g.At a current density of 10 A/g,SAC-1:5 has a capacitance retention rate of 100%after 5000 cycles of charge and discharge.The symmetrical supercapacitor based on SAC-1:5(denoted as SAC||SAC)has a specific capacitance of 104F/g at a current density of 2 A/g,and no capacitance degradation after 3000 charge-discharge cycles at a current density of 10 A/g.In addition,SAC||SAC can provide an energy density of14.4 Wh/kg.(2)Taking the loofah with nature pores as the frame,the petal-like Ni_0.5Mn_0.5Co₂O₄nanomaterial is uniformly grown on the surface by a simple solvothermal method and calcination treatment.It was found that the petals of loofah@Ni_0.5Mn_0.5Co₂O₄nanocomposites(denoted as 2-LNMC)prepared by the reaction system of 100 mg Luffa complex with 0.5 mmol Ni source,0.5 mmol Mn source and 2 mmol Co source were uniformly distributed on the framework provided by loofah under scanning electron microscope,even in the inner pores.At the same time,2-LNMC also exhibits the best electrochemical performance,with a specific capacity of 306 F/g,and a capacitance retention rate of 86.4%at a high current density of 20 A/g.The LNMC||SAC asymmetric supercapacitor based on 2-LNMC and SAC-1:5 has a broadened working potential window of1.5 V and a specific capacity retention rate of 100%after 3000 cycles of charge and discharge at a current density of 5 A/g.Besides,the device can provide an energy density of 18.6Wh/kg.(3)Loofah@Co₃O₄ nanowires composites were prepared by simple hydrothermal reaction and calcination.However,the poor hydrophilicity of the surface of the loofah material makes it impossible to combine with the Co₃O₄ nanowire precursor in an aqueous reaction system.The study found that the addition of CTAB(hexadecyltrimethylammonium bromide)helps the stable combination of the Co₃O₄ nanowire precursor and the surface of the loofah.Scanning electron microscopy results showed that the loofah@Co₃O₄ nanowire composite(denoted as CTAB-LCO)was successfully prepared using CTAB as an additive.CTAB-LCO showed a specific capacitance of 138 F/g at 1 A/g.Meanwhile,at higher current density of 20 A/g,there is a high capacitance retention rate of 88.3%.