Exfoliation of carbon fibers☆☆Keynote Lecture. Original Research Article

Exfoliation of carbon fibers was successfully carried out via intercalation compounds. Intercalation compounds of mesophase-pitch-based and PAN-based carbon fibers were formed by anodic polarization in a nitric and formic acid solutions. Intercalation was confirmed by X-ray diffraction for electrolyzed carbon fibers. Electrolysis behavior suggested that intercalation of either nitric or formic acid into carbon fibers proceeds from the free end of fibers towards the fixed end with increasing electric charges. The intercalation by electrolysis and the exfoliation of intercalation compounds were found to depend on the degree of graphitization of pristine carbon fibers. By rapid heating to 1000 °C in 5 s, marked morphological changes were observed for mesophase-pitch-based carbon fibers; a single fiber was converted to a bundle of thin filaments along the original fiber axis. In the case of PAN-based carbon fibers, scale-like fragments peeled off from original fiber after rapid heating to 1000 °C. The present technique for exfoliation of carbon fibers can be applied to a bundle of long carbon fibers such as 50 cm long and also to carbon fiber fabrics. By passing electric current in the warp of fabric, only the warp was selectively exfoliated. The electric double layer capacitor composed of exfoliated carbon fibers prepared from mesophase-pitch-based carbon fibers showed a high capacitance of 160 F g−1 in a 1 mol dm−3 sulfuric acid electrolyte and about 550 F g−1 in a 18 mol dm−3 electrolyte.