Preparation,Activation And Structural Characterization Of N-Doped Mesoporous Carbon Microspheres And Their Electrochemical Performance

With the ever-increasing depletion of fossil fuel and the emergence of global warming problems,the utilization of renewable and clean energy sources like solar energy and wind energy catches people's universal attention.As such,there was a pressing need for low-cost,environmentally-friendly and advanced devices associated with clean and renewable energy storage and conversion.Representing a class of energy storage devices,supercapacitors,which can provided higher energy density as compared to conventional capacitors and delivered higher power capability as well as longer cycle lifetime than batteries/fuel cells,had recently been receiving considerable attention.Electrode materials is the key of the supercapacitors.Porous carbon materials have been widely used as electrode materials for supercapacitors.An appropriate microstructure can improve the electrochemical performance of carbon-based electrode materials by providing high electrochemically accessible surface area.Additionally,the modification of carbon materials with nitrogen functionalities is one of the most promising method to enhance the capacity while maintaining the superb cycleability of the supercapacitor.Thus,from the point of view of the combination of the electrochemical properties resulted from unique morphological structure and the electrochemical properties endowed by functional doping,the fabrication of nitroge-doping porous carbon materials with unique morphological structure would be of great importance in high-performance supercapacitors application.The research work in this paper were listed as follow:?1?Using triblock copolymer F127 as a soft template,m-aminophenol as a carbon and nitrogen coprecursor,nitrogen-doped ordered mesoporous carbon microspheres with a 2D hexagonal mesostructure has been successfully synthesized through an co-assembly process between F127 and m-aminophenol,and subsequent hydrothermal process.The crystal structure,morphology,mesostructure structure,specific surface area and pore size distribution,surface chemistry of the resultant materials were investigated by XRD,SEM,TEM,nitrogen adsorption-desorption and XPS analysis,respectively.The results showed that the as-prepared materials combined micrometer-sized sphere-like morphology,highly ordered mesoporous structure wih high-level nitrogen doping?up to 3.86 at.%N?.The influence of the amount of triblock copolymer F127,hexamethylenetetramine,1,3,5-trimethyl benzene on the formation of the ordered mesostructure was explored.When the amount of m-aminophenol was fixed at0.275 g,the optimal amount of triblock copolymer F127,hexamethylenetetramine and 1,3,5-trimethyl benzene forming ordered mesostructure were 0.50 g,0.10 g and 0.175 g,respectively.Taking the sample prepared at 800?for example,The electrochemical performance of the obtained materials as supercapacitor electrode materials were studied by cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements.Taking the sample prepared at 800?for example,its specific capacitance was 119 F g^-1 at a current density of 0.2 A g^-1 in 6 M KOH electrolyte aqueous solution in a three-electrode system.At a high current density of 10 A g^-1,the specific capacitance was simply 27 F g^-1.The capacitance retention was 99%after 1000charge/discharge cycles.?2?Nitrogen-doped ordered mesoporous carbon microspheres were physically activated with water vapour.The morphology,mesostructure structure,specific surface area and pore size distribution,surface chemistry of the resultant materials were investigated by SEM,XRD,TEM,nitrogen adsorption-desorption and XPS analysis,respectively.Research have shown that,the obtained carbon materials subjected to water vapour activation retained regular spherical morphology,highly ordered mesoporous structure and high nitrogen content.Moreover,the mesoporous framework of the obtained ordered mesoporous carbon materials was open,leading to a high specific surface area of 1124 m² g^-1.The electrochemical performance of the obtained materials as supercapacitor electrode materials were studied by cyclic voltammetry,galvanostatic charge–discharge and electrochemical impedance spectroscopy measurements.Taking the sample prepared at 800?for example,a high specific capacitance of 288 F g^-1 was achieved at a current density of 0.2 A g^-1 in 6 M KOH electrolyte aqueous solution in a three-electrode system.When the current density was increased to 100 times of the initial current density,the specific capacitance of 222 F g^-1 was still remained,suggesting superior rate performance.Moreover,capacitance retention of95.43%after 5000 charge/discharge cycles was obtained,indicating good electrochemical stability.?3?Nitrogen-doped ordered mesoporous carbon microspheres were chemically activated with KOH.The crystal structure,morphology,mesostructure structure,specific surface area and pore size distribution,surface chemistry of the resultant materials were investigated by SEM,XRD,TEM,nitrogen adsorption-desorption and XPS analysis,respectively.Research have shown that,the obtained carbon materials subjected to KOH activation combined the characteristics of large surface area(up to 3203 m² g^-1),large pore volume with hierarchical porosity(up to 1.93 cm³ g^-1),regular spherical morphology and reasonable amount of nitrogen and oxygen functional groups?up to 6.64%?.The electrochemical performance of the nitrogen-and oxygen-containing micro-mesoporous carbon microspheres as supercapacitor electrode materials were studied by cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements.Benefiting from these unique structural and textural properties,the obtained materials demonstrated excellent electrochemical performance.Taking the sample carbonized at 600?for example,it showed a high specific capacitance of 309 F g^-1 at a current density of 0.1 A g^-1 in a three-electrode system.Even at the high current density of 20 A g^-1,it still retains a relatively high specific capacitance of 229 F g^-1.It also exhibited an excellent cycling stability with only 5%capacitance loss after 10000 consecutive charge/discharge cycles.Moreover,in a two-electrode system,it displayed a high specific capacitance of 261 F g^-1 and outstanding rate capability(retention of 77%from 0.1 to 20 A g^-1)as well as good electrochemical stability of 98%capacitance retention after 9000 cycles.The high current charge and discharge capability,indication of high power density,highlighted the great potential for the application of the nitrogen-and oxygen-containing micro–mesoporous carbon microspheres as electrode materials in supercapacitors which met the need of high power density.