Boron-doped polycrystalline and near-single-crystal quality diamond electro
des were studied by voltammetry. A redox couple with E-1/2 = +1.83 V vs. st
andard hydrogen electrode was detected on the polycrystalline electrodes bu
t was absent on the single-crystal electrodes. The results strongly suggest
that the couple is associated with reactivity at the grain boundaries. Pla
sma fluorination of polycrystalline diamond electrodes using CF4 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 oxyge
n to the surface. Subsequent anodic polarization added additional oxygen an
d made the surface hydrophilic. Single-crystal electrodes also displayed an
increase in oxygen coverage upon both cathodic and anodic polarization. Vo
ltammetry studies of electrodes covered with a thin sp(2) carbon surface la
yer indicate that the redox couple at +1.83 V corresponds to multiple proce
sses including the etching of sp(2) carbon in the grain boundaries. (C) 199
9 The Electrochemical Society. S0013-4651(98)11-068-6. All rights reserved.