Yn. Hu et al., Rotating ring-disk studies of oxidized nickel hydrous oxide: oxygen evolution and pseudocapacitance, J ELEC CHEM, 468(1), 1999, pp. 64-69
A rotating ring-disk electrode (RRDE) method is herein described for studie
s of O-2 evolution on nickel hydrous oxide films, NiOx(hydr.), electrodepos
ited on the gold disk of a Au-Au RRDE in aqueous 1.0 M KOH. This technique
relies on the quantitative detection of O-2 generated at the NiOx(hydr.) \
Au disk electrode during a linear potential scan, by the concentric, bare A
u-ring electrode, which can then be used to determine contributions to the
disk current (I-disk) derived solely from O-2 evolution. Subtraction of suc
h contributions from I-disk in the potential range positive to the trailing
edge of the peak ascribed to the oxidation of the NiOx(hydr.) film reveale
d a constant, positive current when the voltage was scanned in the positive
direction, and a constant. negative current, albeit of smaller magnitude,
in the subsequent scan in the negative direction. This observation suggests
that once account is made for O-2 evolution, the NiOx(hydr.) \ Au-electrol
yte interface in that potential range (0.5-0.65 V vs. Hg\HgO,OH-), behaves
as a (pseudo) capacitor, a model that was further confirmed by monitoring t
he current as a function of the scan rate. The actual values of this pseudo
capacitance were found to be on the order of ca. 80 kF mol(-1) Ni sites in
the film (or equivalently, ca. 0.1 e(-) per Ni site within the potential ra
nge specified above) and, thus, very similar to those reported earlier base
d on current interruption-potential decay and impedance measurements for O-
2 evolution on NiOx(hydr.) grown on Ni electrodes. Implications of these re
sults to the mechanism of self-discharge of NiOx(hydr.) electrodes for alka
line secondary batteries are discussed. (C) 1999 Elsevier Science S.A. All
rights reserved.