Application Of Heteroatom Doped Carbon Materials And Their Composites In Supercapacitors

Carbon-based structures are the most versatile and promising materials utilized in the significant field of energy storage and conversion,and catalysis,due to its excellent surface chemical property,good heat conduction and conductivity,low density and thermal expansivity,devisable specific surface area and pores,and outstanding chemical stability.The properties of carbon materials depend primarily on the choice of raw materials,internal structures and their surface activity.The surface activity is considered to be the main factor affecting the performance of carbon materials.Activation and surface functionalization of carbon materials can significantly change their surface activity,which in turn affects the final properties and uses of the material.The design and synthesis of new low-cost,high-performance carbon materials and the modification of the surface of the structure or loading of other materials make it suitable for different applications and has become a research hotspot in recent years.In particular,the introduction of nitrogen and other heteroatoms in the carbon structure makes it more attractive.The main content of this article is as follow:（1）Hair fibers were employed as a carbon source for the preparation of high-performance porous carbon materials doped with inherent heteroatoms.The electrode performance characteristics in both aqueous electrolyte and organic electrolyte were studied.During the preparation of the material,the carbonization temperature plays a crucial role for the physicochemical properties of the carbon materials.Compared to HMC-700 and HMC-900,HMC-800 material has a higher specific surface area(1306 m²g^-1)and pore volume(0.90 cm³ g^-1).The HMC-800 has a nitrogen content of 8.27%.After made into an electrode,the HMC-800 electrode has a large specific capacitance of340 F g^-1in a 6 mol L^-1KOH solution at a current density of 1 A g^-1.And after 20000 cycles,there is no obvious attenuation.These results show that HMC-800 has good cycle stability and is suitable as an active material for supercapacitors.The HMC-800 material was further assembled into a symmetrical button-type supercapacitor to study its two-electrode electrochemical performance.With an electrolyte of 1 M LiPF₆/EC+DEC,the specific capacity is 126 F g^-1at a current density of 1 A g^-1.（2）3D porous structure carbon materials were prepared by adjusting the proportion of organic salt sodium glutamate and inorganic salt sodium chloride and the carbonization temperature.The carbon material obtained at 800 ^oC carbonization has a specific capacity of 320 F g^-1,and exhibits excellent cycle stability at a current density of 2 A g^-1.After10,000 galvanostatic charge/discharge cycles,the capacity retention is 96%.Such high supercapacitor performance is ascribed to the high active specific surface area and meso-pore size distribution combined with the robust macroporous carbon skeleton,which provides a rich active site for adsorption/desorption.The heteroatoms supported by the carbon skeleton further increase the electrochemical activity,defects and electrical conductivity of the materials that provides a fast Faradaic reaction and additional capacity.In addition,such low-cost green prepared 3D porous materials can be applied to other applications such as gas adsorption,catalyst carriers,and other energy storage/transformation devices.（3）The difference in pore properties of carbon materials prepared from organic salts with different alkali metal components and their corresponding capacitance properties were examined.These porous carbon materials were prepared by directly carbonizing three different organic salts,potassium tartrate,potassium sodium tartrate,and sodium tartrate.This study found that these three kinds of carbon materials have different specific surface areas and pore properties.Potassium tartrate-based carbon materials have the highest specific surface area(1130.3 m² g^-1)and a narrow pore size distribution,mainly existed in the form of micropores;The specific surface area of the sodium potassium tartrate-based carbon material is 650.8 m² g^-1.The pore size distribution in the range of less than 1 nm follows the pore size distribution of the potassium tartrate-based carbon material,while it has smaller pore size distribution in the range of 1-2 nm than the potassium tartrate-based carbon material.Sodium tartrate-based material has a minimum specific surface area of 430.2 m² g^-1and an extremely wide pore size distribution（0-60nm）.Therefore,porous carbon materials with different pore properties can be prepared by one-step carbonization method by screening organic salts of different components,which can be applied to different applications.Potassium tartrate-based carbon materials were used for supercapacitor electrodes.The specific capacity was 286 F g^-1at a current density of 1 A g^-1,and there was no significant attenuation after 5,000 cycles.（4）The composites prepared by simultaneous in-situ grown bismuth metals and carbon materials were synthesized by blending and carbonizing organic salts,strontium nitrate and ammonium chloride.At the same time,the role of introduction of ammonium chloride and strontium nitrate was studied.A suitable proportion of ammonium chloride can contribute to a 3D cross-linked carbon skeleton during carbonization,thereby providing a robust electronic conduction network and electrolyte buffer pool.The Bi/N-TPC material were used as supercapacitor electrode materials and has a high specific capacity of 868 F g^-1,and the material has excellent rate performance.When the current density increases from 1 A g^-1to 10 A g^-1,and the capacity fading is only 5.5%.