Electrochemical characterization of doped diamond-coated carbon fibers at different boron concentrations

Doped diamond films have been deposited on carbon fibers (felt) obtained from polyacrylonitrile at different levels of boron doping. For a successful coating of the fibers, an ultrasonic pretreatment in a bath of diamond powder dissolved in hexane was required. Films were grown on both sample sides, simultaneously, by hot filament-assisted chemical vapour deposition technique at 750 °C from a 0.5% H2/CH4 mixture at a total pressure of 6.5 × 103 Pa. Boron was obtained from H2 forced to pass through a bubbler containing B2O3 dissolved in methanol. The doping level studied corresponds to films with acceptor concentrations in the range of 6.5 × 1018 to 1.5 × 1021 cm− 3, obtained from Mott-Schottky plots. Scanning electron microscopy analyses evidenced fibers totally covered with high quality polycrystalline boron-doped diamond film, also confirmed by Raman spectroscopy spectra. Diamond electrodes grown on carbon fibers demonstrated similar electrochemical behavior obtained from films on Si substrate, for ferri/ferrocyanide redox couple as a function of boron content. The boron content influences electrochemical surface area. A lower boron concentration provides a higher growth rate that results in a higher surface area.