The Preparation Of Porous Carbon Materials Based On Zinc Glucose And Its Capacitance Performance

Supercapacitor is a new type of energy storage device between battery and traditional capacitor with high energy density,fast charge and discharge capacity and long cycle capacity,which is favored by many scientific researchers.At present,carbon materials are extensively used in supercapacitors.The property of the electrode material has a key role in the performance of supercapacitors,so it has become the focus of supercapacitors research.In order to improve the electrochemical performance of supercapacitors,regulating the pore structure of carbon materials and doping heteroatoms are common methods.For preparing electrode materials with high electrochemical performance,zinc gluconate was used to prepare porous carbon in this article.Zinc gluconate is a kind of chemical substance with low cost,simple chemical composition and can realize self-activated during the carbonization process.The zinc element can gradually evaporate during the carbonization process,creating pore structure on the surface of the carbon material,forming a graded porous carbon material.Based on this,this paper took the pore structure regulation as the starting point,and compared the activation effect by using the methods of self-activation without pretreatment,solid-liquid mixed pretreatment activation,solid-solid mixed pretreatment activation and liquid-liquid mixed pretreatment activation,respectively,to explore superior methods of preparing porous carbon materials.The work of this paper is mainly carried out from the following four aspects:（1）Preparation and capacitance properties of zinc gluconate porous carbon materials.Zinc gluconate was used as carbon precursor for direct carbonization,and different carbonization temperatures were set to compare the activation effect and explore its electrochemical performance.The final test results show that zinc gluconate has better self-activation effect at 950℃,and its pore structure and pore size distribution are appropriate.In the three-electrode system test,the capacitance retention rate of Zn PC-950 electrode reached 90.9%after 50000 cycles.In symmetrical supercapacitors with 6 M KOH electrolyte,the specific capacitance can reach 66 F g^-1at 1 A g^-1;In Et₄NBF₄ electrolyte,the maximum energy density of the supercapacitor was 49.8 Wh kg^-1,when the power density was 2477.8 W kg^-1（2）Preparation and capacitance properties of KOH activated zinc gluconate porous carbon materials.On the basis of the prepared porous carbon material with the best carbonization temperature,the carbon powder was mixed with the solution with different amounts of KOH dissolved（solid-liquid mixture）for high-temperature activation,and the activation effect of different KOH dosage were investigated.The final test results showed that KOH activation significantly optimized the pore structure and pore size distribution of carbon materials.According to the analysis of electrochemical performance test results,the specific capacitance of KOH activated carbon material was about twice as high as that of zinc gluconate carbon material,and has excellent performance at different current densities,showing good double-layer behavior and cycle stability.In the three-electrode system,the specific capacitance of porous carbon material reached 171.77 F g^-1 at 0.5 A g^-1 current density.In addition,the symmetrical supercapacitor assembled also had good performance.In KOH electrolyte,when the power density was 498.91 W kg^-1,its maximum energy density reached 15.63 Wh kg^-1.When tested in organic electrolyte,the voltage window was broadened to 2.5 V,which led to further improvement of energy density.The supercapacitor showed maximum energy density of 92.63 Wh kg^-1at power density of 1241.55 W kg^-1.After 10000charge-discharge cycles,the initial specific capacitance could still maintain 94.74%.（3）Preparation and capacitance properties of CaCO₃ activated zinc gluconate porous carbon materials.Nano CaCO₃ was selected as activator and template machine,and it was mixed with zinc gluconate powder（solid-solid mixture）and carbonized at high temperature to obtain graded porous carbon materials.The activation effect and electrochemical performance of different nano CaCO₃ dosage were investigated.The final test results showed that the activation of nano CaCO₃ plays a significant role in regulating the surface pore structure of carbon materials.In the electrochemical test,the specific capacitance of the carbon material reached 137.07 F g^-1 at the current density of 0.5 A g^-1 in the three-electrode system.After being assembled into a symmetrical supercapacitor,it showed a maximum energy density of 11.85 Wh kg^-1 at the power density of 498.25 W kg^-1.At the same time,its performance in organic electrolyte had also improved.The voltage window still reached 2.5 V,and the supercapacitor assembled showed a high energy density of 81.15 Wh kg^-1 at 1240.02 W kg^-1,which maintain 89.66%of the initial specific capacitance after 10000 cycles.（4）Preparation and Capacitive Properties of Nitrogen Doped Zinc Gluconate Porous Carbon Materials by NH₄Cl ActivationNH₄Cl and zinc gluconate powder were dissolved in deionized water（liquid-liquid mixture）at the same time.After drying,heat treatment was carried out to achieve activation and nitrogen doping.By adjusting the amount of NH₄Cl,the pore structure and nitrogen doping amount of porous carbon materials are regulated,and the ideal nitrogen doped porous carbon materials are obtained.The final test results showed that the specific capacitance of the nitrogen-doped porous carbon material reached 221.43 F g^-1 at 1 A g^-1 in the three-electrode system.After being assembled into symmetric supercapacitors,the specific capacitance was also improved due to the introduction of nitrogen atoms.Meanwhile,after calculation,a maximum energy density of 17.18 Wh kg^-1 was achieved at 498.89 W kg^-1.When the symmetrical supercapacitor was assembled with Et₄NBF₄ electrolyte,the voltage window can still be extended to 2.5 V,showing a specific capacitance of 177.84 F g^-1 at 1 A g^-1.And the maximum energy density of 153.44 Wh kg^-1 was achieved at 1242.48 W kg^-1.Meanwhile,85.03%of the initial specific capacitance can still maintain after 10000cycles.