X‐ray photoelectron spectroscopic studies of carbon‐fiber surfaces. 19. Surface chemical changes during electrochemical oxidation in base

Electrochemical oxidation of polyacrylonitrile‐based carbon fibers in a basic electrolyte was studied and the surface chemical changes monitored by core and valence‐band x‐ray photoelectron studies. These studies show that potentionstatic treatment under strongly oxidizing conditions in a sodium hydroxide electrolyte for 20 min leads to a surface consisting of a substantial amount of weakly attached carbonate ions with a lesser contribution from carbosylae and other C/O groups attached to the carbon‐fibre surface. The valence‐band spectrum for a carboxylated carbon fibre calculated by a multiple‐scattered wave Xα calculation on a CO 2 − −Substituted coronene (C 36 O ) shows that a carboxylate‐functionalized carbon fiber would make only a partial contribution to the observed spectrum, which shows considerable similarities with the spectrum of the carbonate ion. The weakly attached carbonate ions were reduced in surface concentration by repeated washing.