Electrochemical treatment has a significant effect on the properties of carbon fibers (CFs). In this study, the effect of mild electric field action on the microstructure and properties of polyacrylonitrile (PAN)-based high-modulus CFs (HMCFs) and high-strength CFs (HSCFs) was investigated. Under the action of a mild electric field, CFs did not show obvious defects, but their microstructure, mechanical properties and electrical properties were affected. For HMCFs, the graphitization degree in both axial and radial directions of the fibers had a decreasing trend, the grain spacing increased, and the grain size and degree of orientation decreased, which led to a decrease in the tensile strength, tensile modulus and axial conductivity. However, for HSCFs, the pattern of change was exactly opposite to that of HMCFs. The results of this study can provide useful guidance for optimizing the production process and surface modification of CFs.

The carbon spheres (CSs) synthesized by an ultrasonic-spray pyrolysis method were activated for supercapacitor electrode. There are plenty of cracks on the surface of the activated carbon spheres (ACSs), which expend with increasing the activation temperature and activator dosage. The specific capacitance of ACSs increases with the activation temperature and activator dosage and reach to maximal value at certain conditions. Importantly, the ACS sample activated at relatively low activation temperature (600 °C) and 7 of mass ratio of KOH to CSs has the highest specific capacitance (about 209 F g− 1 at 50 mA g− 1 of current density) and indicates the excellent cycling stability after 1000 consecutive charge–discharge cycles. Furthermore, the graphene sheets could be found in the samples that were activated at 1000 °C. And the electrode prepared by the sample has the very low series resistance because of the excellent conductivity of the formed graphene sheets.