Synthesis Of Porous Carbon By Cationic Soft Template And Study On Their Supercapacitor Performance

In recent years,supercapacitors have been widely used in various fields due to their advantages such as high power density,good cycle safety and stability,as well as superior charging and discharging performance.Carbon materials have a number of advantages such as simple and convenient materials extraction,low price with low mass,etc.They are the earliest electrochemical supercapacitor electrode materials that have been studied,and their preparation technologies have reached a very high level.In order to obtain supercapacitors with higher electrochemical performance,researchers have various research goals for carbon materials which are used as electrodes,including the ability to achieve precise control of the size of the materials,to achieve a large and highly utilized specific surface area,and to acquire more pathway structures to facilitate the movement of charges.The preparation of carbon materials by the soft template method is characterized by the ability to precisely regulate the materials size and obtain special morphology,which can effectively improve the electrochemical performance of carbon materials.One of the keys to the preparation of carbon materials by the soft template method is the selection of surfactants.Compared with general surfactants,didecyl dimethyl ammonium bromide is characterized by two long chains in the lipophilic part,which interact with each other,facilitating its role as a soft templating agent and increasing the possibility of preparing more special-shaped porous carbon materials.Brominated 1-dodecy 1-3-methylimidazole has the characteristics of both ionic liquid and surfactant,which can form stable micelles,vesicles and emulsion droplets,facilitating the formation of special morphology with more pathway structures inside the carbon materials.Further,by introducing heteroatomic groups（Such as N）into the carbon materials and changing the contact surface of the carbon electrode materials with the electrolytes,the electrochemical characteristics of the supercapacitors and the pseudocapacitance in it can be improved significantly.The main research of the paper are as follows:1.A series of carbon nanospheres（PCMNSs-x-y-z）with different morphologies and sizes were successfully synthesized by using didecyl dimethyl ammonium bromide（a double-chain cationic surfactant）as a soft template agent,tetraethyl orthosilicate（TEOS）as a silicon source,resorcinol and formaldehyde as carbon sources,and the organic base ethylenediamine（EDA）as a source of nitrogen and alkali,which also provided the required acidity and alkalinity for the reaction.The experimental results showed that under the fixed other experimental conditions,with the increase of EDA dosage,the size of the materials changed very small（all around 300-400 nm）,and their morphologies realized from solid spheres,hollow spheres to broken mesh-like fibrous aggregated structures,etc.While fixing the other experimental conditions,the addition of ethanol had a greater effect on the structure and size of the porous carbon materials fabricated by the soft-template interfacial reaction modulation of the doublechain cationic surfactant.The synthesized porous carbon spheres contain nitrogen and have abundant access pores with large pore size（3.65-9.08 nm）,high specific surface area(382396 m²·g^-1)and large pore volume(0.37-0.40 cm·g^-1).Among them,the bowl-shaped materials had high specific surface area(382 m²·g^-1).large pore volume(0.40 cm³·g^-1),large pore size（3.65 nm）and high nitrogen element doping（4.44 at.%）.In the tests of the supercapacitors,it achieved a specific capacity of 146.5 F·g^-1,an energy density of 5.09 Wh·g^-1(at 1 A·g^-1 current density),a high specific capacity of 221.22 F·g^-1 and a high energy density of 7.68 Wh·g^-1(at 0.2 A·g^-1 current density)with a capacity retention rate of 94%after 5,000 cycles(at 10 A·g^-1 current density),reflecting the ideal cycling stability of the electrode materials.2.A variety of carbon nanomaterials（x-y）were successfully synthesized by a simple hydrothermal method using didecyl dimethyl ammonium bromide（a double chain cationic surfactant）as a soft templating agent,but using different chain lengths of aliphatic aldehydes and resorcinol as carbon sources,with most of the particles having a size of about 400-600 nm.In this part of the work,we studied the fixed chain length of aliphatic aldehyde when using organic base EDA as nitrogen source and catalyst,and the size of the resulting porous carbon materials decreased with the increase of ethanol dosage,and the morphology of the materials was basically maintained.As the chain length of aliphatic aldehyde increased,the resulting porous carbon materials changed from complete hollow spheres at the beginning to flower spheres and then to solid-like spheres,as well as the surface roughness gradually became rougher from the original smoother ones.x-y had large pore size（10.10-18.36 nm）,high specific surface area(687-868 m²·g^-1)and large pore volume(1.62-1.74 cm³·g^-1).Among them,the small size carbon particle structure of 20 nm had high specific surface area(868 m²·g^-1),large pore volume(1.74 cm³·g^-1),large pore size（10.10 nm）and high elemental carbon content（95.12 at.%）and high graphitic nitrogen content（32.0 at.%）.In the tests of the supercapacitors,it reached a specific capacity of 108 F·g^-1 and an energy density of 3.75 Wh·kg^-1(at a current density of 1 A·g^-1),with a capacity retention of 90.6%(97.8 F·g^-1)and 85.2%(92 F·g^-1)at high current densities of 3 A·g^-1 and 10 A·g^-1,after 5000 cycles(at a current density of 10 A·g^-1),the capacity retention was 89.3%.3.Two surfactants,including didecyl dimethyl ammonium bromide（a double chain cationic surfactant）and brominated 1-dodecyl-3-methylimidazole（an imidazole cationic surfactant）,were used as soft templating agents,resorcinol and formamide were used to synthesize phenolic resins as carbon sources,where formamide also served to introduce nitrogen elements.Because of the low activity of formamide,it usually only reacts with resorcinol to form oligomers and cannot form polymer precipitates.Carbon micro/nanomaterials（DDAB-x-y-z and[C12mim]Br-x-y-z）with widely different morphology and properties were successfully synthesized in this study by adding a few drops of formaldehyde as the precipitant,and most of the particles were about 300-500 nm in size,which provided a new way to better introduce nitrogen into carbon materials.DDAB-x-y-z and[C12mim]Br-x-y-z had large pore size（1.69-2.35 nm）,high specific surface area(7591159 m²·g^-1),and large pore volume(0.68-1.20 cm³·g^-1).Among them,DDAB-0.44-0.05-20 materials had a special morphology（475 nm,multilayer stacked lamellar structure materials）,high specific surface area(759 m²·g^-1),large pore volume(0.68 cm³·g^-1),and large pore diameter（1.69 nm）.In the tests of the supercapacitors,it reached a specific capacity of 108.8 F·g^-1 and an energy density of 3.78 Wh·g^-1(at a current density of 1 A·g^-1),with capacity retention rates of 80.5%(87.6 F·g^-1)and 48.7%(53 F·g^-1)at high current densities of 3 A·g^-1 and 10 A·g^-1,respectively.The[C12mim]Br-0.84-0.05-20 materials had a special morphology（agglomerated structure of small spheres with very small particle size）,high specific surface area(1159 m²·g^-1),large pore volume(1.20 cm³·g^-1),large pore size（1.79 nm）,in situ selfdoping of the synthesized materials with nitrogen（2.04 at.%）and high oxygen content（5.32 at.%）.In the tests of the supercapacitors,it reached a specific capacity of 123 F·g^-1 and an energy density of 4.27 Wh·kg^-1(at a current density of 1 A·g^-1),with capacity retention rates of 67.6%(83.1 F·g^-1)and 48.0%(59 F·g^-1)at high current densities of 3 A·g^-1 and 10 A·g^-1,respectively,with a capacity retention rate of 95.5%after 5000 cycles(at a current density of 10 A·g^-1).In supercapacitor electrode materials,there are greater prospects for development.