Activation studies of carbon fiber electrodes.

摘要

The activation of the cylindrical portion of carbon fibers was examined. Electrochemical and spectroscopic characterization of four different fibers was performed to determine what surface properties were important for activation. The surface properties before and after treatment were studied with scanning electron microscopy, Raman spectroscopy, thermal desorption mass spectrometry and electrochemical methods. The data showed that the electrochemical activity produced by a particular treatment protocol depended on the precursor material and the fabrication process used to make the fiber. The fibers have a multiphase microstructure with a wide range of surface properties.; Because of the heterogeneity of the fiber properties, a general treatment protocol could not be established. Vacuum heat treatment activation improved the response for all of the AR fibers but the most improvement was observed at fibers, such as the AVCO, with a disordered surface microstructure. The presence of a high fraction of edge plane and the surface cleanliness are important activation parameters. The best electrochemical activity was often obtained after a +2 V square wave treatment at 50 Hz, although varying degrees of activation were observed at different fibers.; The AVCO fiber had an outer skin present which inhibited the electron transfer. The skin was removed by a galvanostatic treatment. The fibers may often have outer skins, sizing material and sheaths of unreactive basal plane that must be removed prior to activation. Since the fibers cannot be mechanically polished to renew the surface, electrochemical methods are quite effective.; The DuPont fiber was observed to undergo severe fracturing and exfoliation after the galvanostatic treatment. The surface area increased by 3-4 orders of magnitude. The fractured surface is highly oxidized with channels along the principal fiber axis. The peak shaped voltammograms for ascorbic acid, dopamine and catechol were explained by a combination of thin-layer effects, adsorption and restricted diffusional pathways. On the other hand, electron transfer for ferrocyanide remained quite irreversible. Interestingly, the fractured fiber could be annealed when vacuum heat treated and the surface area was reduced to prefracture levels. The voltammetric properties were also restored to essentially those of the pre-fractured fiber.