G. Cordeiro et al., ANODIC-DISSOLUTION OF NICKEL IN CONCENTRATED SULFURIC ACIDIC SOLUTIONS, Journal of Applied Electrochemistry, 26(11), 1996, pp. 1083-1092
The anodic dissolution of nickel in concentrated sulfuric acidic solut
ions is characterized by two diffusion plateaux related to the active
and transpassive regions. For the same speed of rotation of a rotating
disc electrode, the two plateaux currents are almost identical. Howev
er, the less anodic one gives rise to a rough electrode surface while
a polished surface is observed at the more anodic one. For nickel as-r
eceived, mass transport influences the current over the whole potentia
l range. After heat treatment, only the current for the two plateaux w
ere mass transport controlled. Electrochemical impedance diagrams show
that the lowest frequency capacitive loop is influenced by mass trans
port. Electrohydrodynamic (EHD) impedance diagrams show two different
regions. In the low frequency range, the results follow the theoretica
l curve corresponding to a uniformly accessible electrode with a very
high Schmidt number around 10(7). At high frequency, the EHD impedance
may correspond to an interface covered by a gel layer formed from the
products of the anodic dissolution.