Preparation And Electrochemical Performances Of Porous Carbon Nanofiber Mats

As a new energy storage component, supercapacitor has been attracting more and more attention because of its high power density, rapid charging/discharging capacity, long lifecycle and potential applications in a broad range of areas from mobile telecommunication, information technology, consumer electronics, electric vehicle, aviation, aerospace, military facility and the like. According to the principle of energy-storage there are two types of capacitors: electric double-layer capacitor and faradaic pseudocapacitor. This work focused on making new electrode materials for electric double-layer capacitor.In this work, new porous carbon nanofibers were first prepared by electrospinning and carbonization process. Emulsion polymerization was used to prepare polymer nanoparticles, which served as the pore templates for making porous carbon nanofibers. The polymer nanoparticles were blended into polyacrylonitrile nanofibers by electrospinning technique. During the carbonization process, the nanoparticle templates were decomposed and left many pores on/in the as-prepared carbon nanofibers. The structures and properties of the as-prepared porous carbon nanofibers were investigated using transmission electrode material (TEM), scanning electron microscope (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analyzer (TGA), N₂ adsorption (BET). Cyclic Voltammetric (CV), constant current charge/discharge and cycle life test were performed to characterize the electrochemical properties of the porous carbon nanofibers as electrodes for supercapacitors.The thesis mainly consists of the following two parts:1. Synthesis and characterization of nano-pore templates: the synthesis of polymer nanoparticles was completed by using styrene as the main monomer, divinylbenzene as cross-linking agent, K₂S₂O₈ as the initiator, DNS-458 and styrene sulfonate as emulsifier, water as dispersion medium. The diameters of the as-synthesized polymer nanoparticles ranged from 15 nm to 25nm, measured by using Atomic Force Microscope. TGA analyses showed that the decomposing temperature of the pore templates was between 400 and 450℃, which ensured that the templates were removed from the matrix and the nano-pores were formed in/on the nanofibers during the carbonization process.2. Preparation and electrochemical characterization of porous carbon nanofibers: polyacrylonitrile as carbon precursor and polymer nanoparticles as pore templates were electrospun into composite nanofibers, which were carbonized to form porous carbon nanofibers by carbonization process. Images of TEM showed that the as-prepared porous carbon nanofibers had a diameter range from 100-200nm with pore size from 10-20nm. The measurement of the electrochemical properties of the porous carbon nanofibers was carried out by using cyclic voltammetry and constant current charge-discharge test in 1mol/L H₂SO₄ solution. As a result, the supercapacitor based on the porous carbon nanofiber electrodes has a good electric double layer performance with a maximum specific capacitance of 260F/g, which is 3 times than the capacitor based on the non-porous carbon nanofiber electrodes. Cyclic tests were performed by galvanostatic charge/discharge method at a current density of 1A/g and indicated that the porous-carbon-nanofiber-based capacitors had long cycle durability. After 1000 cycles, their capacitance decays are not beyond 6%, from 260 to 240F/g. At the same time, the thickness of the electrode did not have a significant influence on the specific capacitance, which could retain 235F/g even when the thickness of the electrode was 2mm. This will be very useful for decreasing the amount of metalic charge collector in capacitor.