Preparation And Application Of Nitrogen And Sulfur Dual-doped Porous Carbon Electrode Material For Supercapacitor

With the rapid development of the global economy and growth of human population worldwide, global energy consumption has been accelerating at an alarming rate and serious environmental problems have significantly threated to the survival and development of mankind. Among various energy conversion and storage devices, supercapacitors and lithium-ion batteries has attracted a great deal of attention from industry and academia, mainly due to their broad propect of application. Supercapcacitors current bridge the power gap between batteries and traditional capacitors, delivering higher power bursts than batteries and storing more energy than capacitors. However supercapacitors currently suffer some problems such as low energy density and high cost, it is necessary to develop a high energy density, low cost, perfect performance and good stability electrode materials. Carbon materials are considered prospective electrode materials for industrialization, but simple environmental friendly process for preparing carbon materials and the surface modification of carbon materials still need to study.(1)The pre-preliminary exploration of preparation of the activated carbon electrode materials revealed that direct carbonization of chill straw and activation by KOH/Na OH are environmental, cost-effective methods to prepared high performance electrical double-layer capacitors. The content of conductor in electrodes was studied in the range of 2.5%- 10% in 0.5 mol/L H2SO4。The results show that the electrodes materials with 5% acetylene black have higher reaction current and performance of capacitance. 0.5 mol/L H2SO4、0.5 mol/L Na2SO4 and 1 mol/L KOH electrolyte was employed to study the effects of electrolyte on the performance of supercapacitors. Due to suitable ions size matching the activated carbon o[porous diameter, electrode materials have higher capacitance in 0.5 mol/L H2SO4.These remarkable results demonstrate the exciting commercial potential for high rate, highly stable and low-cost electrochemical energy storage devices, which provides a new method to solve the problem of the preparation process of the commercial supercapacitors.(2) We explore a new synthesis method for Nitrogen and Sulfur dual-doped porous carbon(NSMCs) using an improved method as mentioned above for reference. NSMCs have been fabricated through a facile template-mediated pyrolyzing method using poly(ethyleneimine)(PEI) as sources of nitrogen(N) and carbon(C), ferrous sulfate(Fe SO4·7H2O) as both precursor of sulfur(S) and activation reagent along with nanoscaled silica as sacrificial supports. The composition, morphology, and microstructure of the products are characterized using X-ray diffraction, scanning electron microscopy, nitrogen sorption analysis and X-ray photoelectron spectroscopy. It reveals that these NSMCs possess a BET surface area over 1064 m2/g and abundant mesoporous structure with pore size ranged from 4 to 20 nm. The atomic percentages of N and S functionalities are found to be 4.00 at.% N and 0.83 at.% S, indication of successful incorporation of both nitrogenand sulfur into carbon network. Benefiting from the aforementioned characteristics, these NSMCs show perfect supercapacitive performances, which have been demonstrated by cyclic voltammetry and constant-current charge/discharge cycling techniques. In 0.5 M H2SO4 electrolyte, the specific capacitance(SC) of the as-prepared NSMCs electrode can reach 280 F/g at a current density of 1 A/g. Even at a high rate capability of 100 A/g, the NSMCs electrode still shows the SC value as high as 232 F/g, retaining 83% of that at 1 A/g. Also, the electrode exhibits excellent charge discharge cycling stability, and no measurable capacitance losses is observed even after 5000 cycles, making them potentially promising for high-performance energy storage devices.(3)In order to further improve the electrochemical performance of NSMCs, NSMCs/CNTs was successfully prepared by mechanical blending. In 0.5 mol/L H2SO4 electrolyte, the specific capacitance of the as-prepared NSMCs/CNTs electrode can reach 300 F/g. We also employed different concentration electrolyte, different mixing ratio as a representative system to find a most optimal electrode material. The results show that the best proportion of NSMCs and CNTs is 8:1,and the optimal NSMCs/CNTs electrode materials have high electrical conductivity, good electrochemical stability, low-cost and high capacitance, respectively in 0.5 mol/L H2SO4, 1.0 mol/L Na2SO4 and 1.0 mol/L Na OH, which can meet the requirements of the applications in low-cost and long-life cycles energy storage devices.