Effect of the graphitization degree for electrospun carbon nanofibers on their electrochemical activity towards VO2+/VO2+ redox couple

In order to investigate the effect of the conversion of carbon structure for electrospun carbon nanofibers (ECNFs) on their electrochemical activity toward vanadium redox couple, ECNFs with different graphitization degree are prepared through the catalytic graphitization process and their physico-chemical properties have been characterized systemically. The results show that both of the iron catalyst and catalytic graphitization temperature contributes to improve the graphitization degree of the ECNFs greatly. With the increase of iron (III) acetylacetonate (AAI) mass ratio and catalytic graphitization temperature, the graphitization degree of ECNFs increases continuously, while its electrochemical activity increases at first and then decreases. Despite the XPS results show that the O and N content may not have a significant effect on the electrochemical activity of ECNFs, the heteroatoms at the edge-plane definitely are beneficial to the vanadium redox reactions. Based on these, it can be concluded that plenty of edge planes of graphite crystallites are generated during the conversion of carbon structure and more heteroatoms at the edge-plane may act as the active sites for VO2+/VO2+ redox reaction. It is to say, the carbon materials with an appropriate graphitization degree exhibit the best coupling effect of the conductivity and electrocatalytic activity, which have a big influence on the electrochemical activity of carbon materials.