Synthesis Of Porous Heteroatom-doped Carbon Materials For Supercapacitor

Nowadays,with the continuous development of society,environmental pollution also comes.In this era of advocating the Green and environmental protection,we have new requirements for energy technology.Unlike traditional energy technologies,the emerging energy technologies need to be more advanced,more practical and more environmentally friendly.supercapacitors are a new type of green and environment-friendly energy storage device.At the end of the 1980s,the development of supercapacitors began to become a hot topic due to the development requirements of new energy vehicles.The performance of supercapacitors is mainly affected by the electrode,so the choice of electrode material becomes the key to the supercapacitors with good performance.Porous carbon materials have become the competitive electrode materials for supercapacitors due to their large specific surface area,stable physicochemical property and simple preparation method.In order to further improve the electrochemical property of supercapacitors,we try to introduce heteroatoms into porous carbon materials.The presence of heteroatoms can not only make the electrode materials have better wettability and conductivity,but also provide more active sites for ions to contact with the electrode.In this research subject,we chose polyvinylidene fluoride?PVDF?as the carbon source material,introduced hetero-atomic groups through physical or chemical methods,used hard templates or soft templates to introduce mesopores,so as to prepare porous materials with sufficient heteroatom content and appropriate porous structure.The main works in this research are shown in the following text:?1?Nitrogen-containing porous carbons with numerous micropores were prepared by polyvinylidene fluoride?PVDF?following potassium hydroxide?KOH?activation at 600–900?for 2 h under N₂ atmosphere.The obtained nitrogen-containing porous carbons have a large specific surface area of approximately 2289 m² g^-1,a certain nitrogen content of 1.35 at.%and a favorable hierarchical porous structure possessing a great number of micropores and a part of mesopores.The carbon material exhibits high specific capacitance of 338 F g^-1 at 0.5 A g^-1 in a 6 M KOH solution and outstanding cycling property of 91.6%maintenance at 2 A g^-1 after10000 cycles.An all-solid-state symmetrical supercapacitor with these as-prepared materials as electrodes can deliver energy densities of 21.9 to 10.4 W h kg^-1 at power densities from 700.8to 12910.3 W kg^-1.?2?The N/P co-doped hierarchical porous carbon materials are synthesized by SiO₂-template approach following potassium phosphate activation.Polyvinylidene fluoride is used as the carbon source,melamine as the nitrogen source and potassium phosphate as the phosphorus source and activator.The obtained porous carbon materials exhibit a hierarchical pore structure?⁰.6 and⁴ nm?,a large specific surface area(1431 m² g^-1)and a high nitrogen and phosphorus content.These predominant characteristics enable the CNP-5-800 sample to exhibit a superior specific capacitance of 337 F g^-1 at 0.5 A g^-1 and outstanding cycling stability of 97.8%retention after 10000 cycles in a three-electrode system.Even in the two-electrode system?an all-solid-state symmetric capacitor?,this kind of materials still can deliver an energy density of 23.1 W h kg^-1 to 12.4 W h kg^-1 at power densities of 720.4 W kg^-1 to 13950 W kg^-1,respectively,and have a cycling property of 98.7%maintenance after 5000 cycles.?3?A porous carbon precursor is prepared by modifying polyvinylidene fluoride with nitrogen via a chemical polyreaction and then introducing mesopores using the soft-template method.After carbonization at the appropriate temperature,the obtained carbon material could be applied in supercapacitors without further treatment.The resulting material exhibits not only a comparatively stable nitrogen content that is very close to the nitrogen content of its precursor but also an effective hierarchical porous structure?⁰.68 and⁴ nm?.The large specific surface area of the carbon material(up to 1688 m²·g^-1)is also an important factor influencing its excellent electrochemical performance.When tested using 6 M KOH as an electrolyte in a three-electrode system,CN-900 exhibits a specific capacitance of 355.6 F g^-1 at 1 A g^-1.When tested using the same electrolyte in a two-electrode system,CN-900 shows a specific capacitance of 84.08 F g^-1 at 0.5 A g^-1.In addition,the carbon material can maintain 98.4%capacitance after 8000 charge/discharge cycles at a current density of 2 A g^-1.The performance of CN-900 is further tested in a two-electrode solid-state supercapacitor with sulfuric acid/polyvinyl alcohol as the electrolyte,and a specific capacitance of 90.31 F g^-1 is observed at 1 A g^-1.