Iv. Aoki et al., Ac-impedance and Raman spectroscopy study of the electrochemical behaviourof pure aluminium in citric acid media, ELECTR ACT, 46(12), 2001, pp. 1871-1878
The electrochemical behaviour of pure aluminium in citric acid solution was
investigated with a rotating disk electrode (RDE) at the open circuit pote
ntial (OCP). in the presence and in the absence of chloride, using electroc
hemical impedance spectroscopy and Raman spectroscopy. The impedance diagra
ms are composed of four frequency domains: at very high frequency (VHF), a
Warburg-like: behaviour was attributed to the porosity effect of the extern
al part of the oxide layer. A slightly depressed capacitive loop at high fr
equency (HF) was explained as the combination of two capacitive loops, one
corresponding to the same phenomenon as in the VHF domain but insensitive t
o the porosity (barrier layer resistance in parallel to the oxide film capa
city), the other one to the charge transfer resistance in parallel to the d
ouble layer capacity. An inductive loop at low frequencies (LF) appeared as
due to the relaxation of oxygen species adsorbed at the film \ solution in
terface. while the very low frequencies (VLF) capacitive loop was ascribed
to the coverage relaxation of adsorbed citrate species. possible modulation
of the passive layer thickness was also envisaged as a phenomenon at the o
rigin of this: latter loop. The diagrams shape is also insensitive to the a
ddition of 104 ppm chloride inns to the solution. even though a diameter de
crease of the HF capacitive loop is observed together with an increase of t
he frequency response. Raman Spectroscopy showed that citrate ions adsorb s
trongly to the electrode surface and that the time scale of this process is
consistent with the frequency domain observed for the VLF capacitive loop.
The interaction of citrate with the oxide la!:er is hindered by the additi
on of chloride ions to the electrolytic solution. (C) 2001 Elsevier Science
Ltd. All rights reserved.