Coupling effect between the structure and surface characteristics of electrospun carbon nanofibres on the electrochemical activity towards the VO2+/VO2+ redox couple

In order to investigate the structure-function relationship of electrospun carbon nanofibres (ECNFs), polyacrylonitrile (PAN)-based electrospun carbon webs (ECWs) have been developed, consisting of ECNFs carbonized over the temperature range of 1000–1500 °C in a nitrogen atmosphere. The surface morphology, microstructure, composition, electrical conductivity and hydrophilicity of the ECNFs have been characterized. The electrochemical activity of the ECNFs towards the VO2+/VO2+ redox reaction has been measured by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It is worth noting that the electrochemical performance of the ECNFs decreases firstly and then rises gradually with the increase in carbonization temperature, and a carbonization temperature of about 1300 °C is the turning point. This unusual phenomenon might be attributed to the coupling effect between the surface and structure characteristics of the ECNFs towards the VO2+/VO2+ redox couple. The surface composition plays a leading role in the electrochemical activity of ECNFs carbonized over the temperature range of 1000–1300 °C; however, the edge planes of graphite crystallites which form during the high temperature range from 1300–1500 °C then become the dominant factor. Therefore, the electrochemical activity decreases with the reduction of functional groups on the surface from carbonization at 1000–1300 °C, and then increases with the addition of the edge planes of graphite crystallites from carbonization at 1300–1500 °C.