Preparation And Electrochemical Properties Of Heteroatom-Doped Hierarchical Porous Carbon From Waste Sugar Solution

In the industrial production process of vitamin C,a large amount of waste sugar solution is generated,which is difficult to be directly and efficiently utilized as a strong acidic organic waste.The main component of the waste sugar solution is 2-keto-L-gulonic acid.Its molecular structure is similar to that of biomass such as glucose,and it contains low ash content and high organic impurities.It is a potential precursor for the preparation of porous carbon materials.In addition,electric double layer capacitors?EDLC?as a potential energy storage device has many advantages,such as fast charging/discharging rate,developed pores and stable properties.Heteroatom doping is one of the effective methods to improve the electrochemical performance of EDLC,because the functional groups on the surface could not only obtain an effective specific surface area by improving the wettability of the porous carbon material,but also produce tantalum capacitors by the Faraday reaction.In addition,electrolyte ions could be rapidly transferred in their pores according to the specific pore size distribution?micropores,mesopores,and macropores?of the hierarchical porous carbon and the developed porosity,thereby achieving good rate performance.In this paper,heteroatom-doped hierarchical porous carbon was prepared by using waste sugar solution as precursor.It was used as carbon-based electrode material for EDLC,and the influence of preparation conditions on the electrochemical performance of the hierarchical porous carbon was investigated.The main content includes the following two parts:In the first part,high oxygen content hierarchical porous carbon was prepared.The waste sugar liquid was pretreated by suction filtration to remove insoluble impurities,and the mixture of the waste sugar solution and the lignin was carbonized,and the oxygen-doped graded porous carbon was prepared in combination with KOH activation.The lignin has a three-dimensional network structure and a high oxygen content.The addition of lignin could increase the specific surface area and oxygen-containing functional groups of the porous carbon,but the excessive lignin addition causes the pores to collapse,and the specific surface area of the porous carbon was reduced.In this paper,the effects of lignin addition,carbonization conditions and activation conditions on the pore structure and electrochemical properties of oxygen-doped graded porous carbon were investigated.When 1 g lignin was added,the carbonization temperature was 600°C,the activation temperature was 600°C,and the activation ratio was 3:1,the prepared graded porous carbon had a higher specific capacitance value of428 F/g?40 mA/g?.Meanwhile,the current density of 5 A/g after the 12,000 cycles,presenting a good cycle performance and capacity ratio?96%?,and an energy density of 12 Wh/kg.In the second part,nitrogen-doped hierarchical porous carbon was prepared.Urea was added during the hydrothermal process,Mg?OH?₂ is carbonized as a templating agent,and nitrogen-doped graded porous carbon was prepared by KOH activation.The study found that changing the amount of urea added and activation conditions could effectively regulate the pore structure of porous carbon.Porous carbon prepared when12 g urea was added and the activation ratio was 3:1,wherein the pore volume was0.501 cm³/g,which was higher than that of urea?0.225 cm³/g?and only template?0.410cm³/g?.The specific capacitance of up to 366 F/g at a current density of 40 mA/g,and activated carbon has good electrochemical performance.In summary,this study not only handled the waste sugar solution easily and efficiently,but also realized the high added value utilization of waste sugar solution,and explored the influence of preparation conditions on the pore structure and electrochemical performance of hierarchical porous carbon materials.