Boron Doped Nanocrystalline Diamond Grown on Reticulated Vitreous Carbon: Morphological, Structural, and Electrochemical Characterizations

Reticulated vitreous carbon (RVC) is a macroporous material with high surface area, rigid structure, low resistance to fluid flow and high thermal and electrical conductivities. RVC has a wide range of applications as porous electrodes, high temperature insulation, filters, storage batteries, among others. Composites formed from diamond grown on sp² bonded carbonaceous materials have already been studied, but there are still few publications about the electrochemical properties of this material. Then, the study of new hybrid nanomaterials is very important for understanding and promoting new technologies. In this work, boron-doped nanocrystalline diamond (BDND) films were deposited on RVC heat treated until 1000 °C and 1700 °C in order to evaluate the influence of different structural organization indexes of RVC on the nanocrystalline diamond grains formation as well as on their electrochemical performance. RVC was processed using poly(furfuryl) alcohol and polyurethane foams with 70 ppi (pores per inch) as mold. RVC substrates surfaces were prepared using seeding treatment in which samples are dipped in a 10 wt% solution of Poly diallyldimethylammonium chloride (PDDA) during 30 min followed by immersion in a nanodiamond (4nm) seeding dispersion for 10 min. The seeding step is necessary to improve diamond growth on carbon fiber in order to keep the surface carbon in sp³ configuration dominant over sp² bond etching during diamond film growth. BDND films were grown on RVC heat treated until 1000 °C and 1700 °C using a hot-filament chemical vapor deposition (HFCVD) reactor. The boron doping was performed by dissolving B₂O₃ in methanol in a bubbler attached to the reactor. The solution was prepared with a concentration of B₂O₃ dissolved in CH₃OH that correspond to B/C ratio of 30000 ppm. Hydrogen gas was used as a carrier with a constant flow of 30 sccm. The composites were evaluated by Scanning Electron Microscopy (SEM), Raman spectroscopy and cyclic voltammetry. Raman spectra and SEM images confirmed the BDND films achievement showing the RVC completely covered by a diamond coating. The electrochemical measurements were made by using Autolab PGSTAT 302 equipment with a three-electrode cell. The BDND/RVC composites obtained with different RVC heat treatment temperature (HTT), were used as working electrode. A platinum coil wire served as the counter electrode and Ag/AgCl was used as the reference electrode. The voltammetric curves (VC) were taken in   H₂SO₄ 0.5 mol.L^-1 and showed a standard wide potential window as expected for BDND electrodes. In order to characterize the electrochemical kinetic we have applied CV using the redox couple of Fe(CN)₆^3-/4- with different scan rates. This redox system includes reactions that depend on the specific interactions with the surface electrode. Besides, the electrode kinetics for this kind of redox couple tends to be more sensitive to the surface functionalities on sp²-bonded carbon electrodes. The BDND grown on RVC with higher HTT demonstrated the fast kinetics attributed to the better conductivity of such substrate.