Microwave-Assisted Oxidation of Electrospun Turbostratic Carbon Nanofibers for Tailoring Energy Storage Capabilities

We report the systematic structural manipulation of turbostratic electrospun carbon nanofibers (ECNFs) using a microwave-assisted oxidation process, which is extremely rapid and highly controllable and affords controlled variation of the capacitive energy storage capabilities of ECNFs. We find a nonmonotonic relationship between the oxidation degree of ECNFs and their electrocapacitive performance and present a detailed study on the electronic and crystalline structures of ECNFs to elucidate the origin of this nonmonotonic relation. The ECNFs with an optimized oxidation level show ultrahigh capacitances at high operation rates, exceptional cycling performance, and an excellent energy-power combination. We have identified three key factors required for optimal energy storage performance for turbostratic carbon systems: (i) an abundance of surface oxides, (ii) microstructural integrity, and (iii) an appropriate interlayer spacing.