Voltammetry Studies of Single‐Crystal and Polycrystalline Diamond Electrodes

Boron‐doped polycrystalline and near‐single‐crystal quality diamond electrodes were studied by voltammetry. A redox couple with vs. standard hydrogen electrode was detected on the polycrystalline electrodes but was absent on the single‐crystal electrodes. The results strongly suggest that the couple is associated with reactivity at the grain boundaries. Plasma fluorination of polycrystalline diamond electrodes using in a radio frequency plasma eliminated the redox couple at +1.83 V but did not alter the potential range of water stability. Cathodic polarization of as‐grown, polycrystalline diamond electrodes caused an irreversible addition of oxygen to the surface. Subsequent anodic polarization added additional oxygen and made the surface hydrophilic. Single‐crystal electrodes also displayed an increase in oxygen coverage upon both cathodic and anodic polarization. Voltammetry studies of electrodes covered with a thin carbon surface layer indicate that the redox couple at +1.83 V corresponds to multiple processes including the etching of carbon in the grain boundaries. © 1999 The Electrochemical Society. All rights reserved.