Study On The Preparation And Capacitive Performance Of Phenolic Resin Based Porous Carbons Via A Multiple Pore-creating Method

Supercapacitors have attracted increasing interest as the promising energy storage device owing to their unique characteristics such as high power density,fast charge/discharge rate,and long cycle life.Electrode material is the key factor which influences the performance of supercapacitors.Carbon based materials are the most important electrode materials for supercapacitors due to their high surface area,high electric conductivity,well-developed pore-size distribution,and good chemical stability,etc.Porous carbons with hierarchical porosity micropores,mesopores and macropores are considered as the most desired source of supercapacitor electrode material compared to the other carbon based materials recently.The preparation of porous carbons with well-developed pore-size distribution,relatively low price and good electrochemicalperformance can greatly accelerate the development of the supercapacitorIn this work,we prepared porous carbon via a multiple pore-creating method by using phenolic resin as carbon precursor and sodium carbonate or some organic salts as pore generators.The influences of preparation technology and conditions on the pore structure and the pore-forming mechanism were discussed.The electrochemical performance of the prepared porous carbons in 7 molL^-1 KOH were investigated.The relationship of the electrochemical performance and pore structures and the chemical compositions of the porous carbon were clarified.The main work and contributions of this research are as follows:?1?Via a one-pot strategy,porous carbons were successfully fabricated by using water-soluble phenol formaldehyde resin as carbon precursor and Na₂CO₃ as pore generators.The highest specific surface area and total pore volume of the prepared samples were 1357 m²g^-1 and 0.80 cm³g^-1,respectively.Utilized as an electrode material for electrochemical supercapacitors,the as prepared samples showed a high capacitance of 206 Fg^-1 at a current density of 0.05 Ag^-1,and an excellent rate performance(63%capacitance retention at 20 Ag^-1).Furthermore,the carbon retained about 97.5%of its initial capacitance over continuous 5000 charge-discharge cycles at 2 A g^-1,suggesting good electrochemical stability.Research indicates that when being annealed below 850?,Na₂CO₃ only acted as a template for the formation of micropores.While annealing temperature increased more highly,Na₂CO₃ began to play its activating role to fabricate a 3D hierarchical porous structure with additional mesopores and macropores.?2?The porous carbon materials were prepared by using various organic salts such as sodium acetate,potassium acetate and sodium citrate as pore generators.Research shows that comparing with sodium carbonate as pore generators,the surface area of porous carbon material produced by organic salt is higher,and the pore structure is easier to adjust.Among these three organic salts,sodium acetate is not only economical and has the advantages of simple process,but also has excellent electrochemical performance when used as electrode material for supercapacitors.The as-prepared sample with a high specific surface area up to 1434 m²g^-1 as a supercapacitor electrode exhibits a high specific capacitance of 236 Fg^-1 at 0.05 Ag^-1.Besides,the electrode shows high rate capability with 75%retention rate from 0.05 to 20 Ag^-1.Research shows that sodium acetate broken down into sodium carbonate and some other small molecule gases between 400-500?,and the subsequent pore-forming process is the same as that of the sodium carbonate.Due to the pore-forming effect durning the decomposition of sodium acetate,the specific surface area and total pore volume of the porous carbons prepared by using sodium acetate are much higher than that of Na₂CO₃.?3?Phenolic resin derived nitrogen-doped hierarchical porous carbons were prepared by using sodium acetate as activation agent and hexamethylenetetramine as nitrogen source.The results show that the obtained sample reaches a maximum specific surface area of 1591 m²g^-1 and a high N content of 6.2 at.%.Benefiting from the optimum balance between high nitrogen content and relatively large surface area,the sample exhibits a high specific capacitance of 352 Fg^-1 in a three-electrode system.Furthermore,it also shows excellent long cycle stability in a two-electrode cell?95.3%retention after10 000 cycles?.?4?On the basis of the preparation of porous carbon materials using sodium acetate as pore generator,by extra adding nano-zinc oxide can effectively adjust the pore structure of porous carbon materials.The porous carbon materials with larger pore diameter and high mesoporous ratio are obtained under the synergistic effect of the two pore generators.Test shows that the obtained porous carbon materials not only owns a high surface area of 1949 m²g^-1 and a large total pore volume of 1.53 cm³g^-1,but also a high mesoporous ratio of 51.6%.The electrochemical properties of the obtained porous carbon materials have been greatly improved by the high mesoporous ratio.The sample shows an excellent rate performance of 74%capacitance retention in the range of 0.05Ag^-1 to 100 Ag^-1.Moreover,the electrode material shows an outstanding stability even after 10000 cycles with 97.3%retention of the initial capacitance,indicating excellent cyclic stability.