Study On Supercapacitive Performance Of Activated Carbon Fiber And Its Composite Material

As a new energy storage device, supercapacitor with high power density andlong cycle life have attracted great attention to their promising applications in portableconsumer electronic devices, hybrid electric vehicles, and even heavy-duty industrialscale systems. Among various carbon electrode materials, activated carbon fibers(ACF) have a number of advantages, such as large surface areas, good conductivityand excellent flexibility. In this study, the researchers focused on the synthesis ofactivated carbon fiber, its surface modification and its composite material to revealthe effects of specific surface area, pore size distribution and surface properties ofmaterials on the electrochemical properties, and the synergistic effect of composite.The main studies are as follows:Using PAN-based precursor fiber as raw material, the original activated carbonfiber (OACF) was prepared by carbonization and carbon dioxide activation withdifferent activation time (1h,3h and5h). Crystallization, morphology, specific surfacearea and pore size distribution of the prepared materials were tested by X-raydiffraction, scanning electron microscope, nitrogen adsorption and Raman spectra.The electrochemical performance was measured by cyclic voltammetry, galvanostaticcharge-discharge, and electrochemical impedance spectroscopy in6M KOH aqueouselectrolyte using a symmetric two-electrode system. The result showed that thespecific surface area of the3h sample reached a maximum of469m2g-1. Hence thespecific capacitance of the3h sample was as high as140Fg1at a current density of0.5mAcm-2.To make surface modification on OACF, we thermally treated OACF by nitric acidwith different concentration of35%,65%and95%. Nitric acid thermal treatment ofactivated carbon fibers was realized by two simple steps: firstly the PAN based OACFwere immersed into nitric acid and then the fibers wrapped with nitric acid were treated at80C for present time. As a result, the ACF thermally treated by65%nitricacid had more C-O functional groups with a less loss of specific surface area (468m2g-1to428m2g-1), which led to a maximum of the accessible specific surface areaand high pseudocapacitance. Hence the capacitance had54%increases compared withOACF from139Fg-1to214Fg-1at a current density of0.5mAcm-2and it remained160Fg-1as the current density increased to100mAcm-2. The capacity retention wasstill close to100%after3000cycles.The composite of activated carbon fiber and manganese dioxide was prepared byin situ microwave hydrothermal synthesis of potassium permanganate and OACF.Physical properties of materials with different proportion were measured to showcontent of manganese dioxide, crystallization, surface morphology; electrochemicalperformance was tested in1M sodium electrolyte by a three-electrode system. Theresult showed that the electrochemical performance of the composite containing63%manganese dioxide was the best. This was attributed to the combination of goodelectrical conductivity of ACF and high capacity of manganese dioxide. The capacitywas130Fg-1at a current density of0.5mAcm-2, but under a high current density of50mAcm-2its capacity was still as high as94Fg-1which was excellent comparedwith3Fg-1of manganese dioxide and27Fg-1of OACF.