Preparation Of Templated Carbon And Nitrogen Doped Carbon Electrode Materials From Waste Sugar Solution

Electric double layer capacitor（EDLC）is a new type of energy storage device,which has the characteristics of long cycle life,high power density,and environment-friendly.Electrode materials are the key components of EDLC,which play a decisive role in the electrochemical performance.Carbon materials are widely used in EDLC electrode materials because of their excellent properties.It is the focus and difficulty to select economic and environmental precursors to prepare high-performance porous carbon materials to achieve higher energy density and power density.Waste sugar solution（WSS）is a kind of wastewater produced in vitamin C industry,which is difficult to be treated.If it is discharged directly,it will pollute the environment.However,WSS is rich in organic acids and furans because of its high carbon and oxygen content.At the same time,WSS has rich oxygen-containing functional groups and high reaction activity.It can not only synthesize oxygen doped activated carbon by hydrothermal method,but also realize nitrogen doping by polymerization.Using WSS as precursor,high specific surface area carbon material was prepared and used as electrode of EDLC.Industrial wastewater could be turned into treasure,and high efficiency and high added value utilization of WSS were realized.Hence,we investigate the effects of optimizing the pore structure and introducing surface functional groups on the properties of porous carbon such as morphology,elemental composition and specific surface,respectively,and then investigate the effects on the electrochemical performance of EDLC.Firstly,nano-CaCO₃ was used as a hard template,mixed with waste sugar residue and KOH,and then activated at 800 ^oC to explore the effects of CaCO₃ ratio on the specific surface area and pore size distribution of template carbon.CO₂,a product of CaCO₃ decomposition,acts as a gas activator for pore expansion,and Ca O is used as a hard template to construct 3D carbon skeleton.The average pore size of the template carbon increases and the specific surface area of mesopores increases.When the ratio of CaCO₃ to WSS is 1:2,AC-0.5 possesses a large specific surface area of 2402 m²/g and a specific capacitance of 229 F/g at 2 A/g.The assembled symmetric EDLC exhibits high energy density of 5.48 Wh/kg.After 5,000 cycles,the specific capacitance retention rate was 95.6%.Then,porous carbon was prepared by using soluble salt Na Cl/Na₂CO₃ as template,and templated carbon was prepared by KOH one-step activation method.As a structure directing agent,Na₂CO₃ can promote the generation of 3D structure.The addition of Na Cl can increase the disorder degree of the template carbon and promote the specific surface area of the templated carbon.When the activation temperature is 700 ^oC,and the mass ratio of Na Cl,WSS and KOH is 0.5:1:2,the specific capacitance of DC700-2-0.5 can reach 264 F/g（at the current density of 5 A/g）,the energy density of is 3.44 Wh/kg.A nitrogen/oxygen-enriched copolymer was synthesized via a facile polymerization of WSS,melamine and formaldehyde.Subsequently,nitrogen-doped porous carbon was prepared by carbonization/activation method.It was found that nitrogen-doped porous carbon showed better electrochemical performance than non nitrogen-doped activated carbon.The effects of melamine content and activation temperature on the physical and chemical properties of materials and the performance of EDLC were studied in detail.Remarkably,When the activation temperature is 700^oC and the amount of melamine is 6%,benefiting from an ultrahigh specific surface area（3612 m²/g）and rich heteroatom doping amount（4.3%for N,8.8%for O）,AMP-6%-700 delivers the maximum specific capacitance of 387 F/g at 50 m A/g.Additionally,the assembled symmetric EDLC exhibits high energy density of 10.83Wh/kg at 11.10 W/kg.Furthermore,AM-700 was synthesized by direct pyrolysis of melamine and WSS,and the effects of two nitrogen doping methods on the physical/chemical properties and electrochemical performance of the material were studied.The paper has 34 pictures,9 tables,and 119 references.