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The influence of fluoride on the anodic dissolution kinetics of titanium was studied by several electrochemical techniques at steady-state open-circuit potentials in 1.0 M HClO 4 containing fluoride with various concentrations ranging from 0 to 0.1 M. The promoting effect of fluoride (especially when [F - ] > 1 × 10 -3 M) on the anodic dissolution behavior of titanium was characterized and discussed by taking into account the changes in the estimated electrochemical and kinetic parameters. The faradaic impedance for the anodic dissolution of titanium was analyzed both by fitting based on an equivalent electrical circuit model and by theoretical derivation based on a two-step mechanism involving one adsorbed intermediate species. By correlating the faradaic impedance expression derived from the dissolution mechanism with that deduced from the equivalent electrical circuit model, some important kinetic parameters (such as the apparent rate constants K 1 and K 2 and the surface coverage θ ss ) could be estimated from the equivalent circuit elemental parameters (such as R c1 , R a , and C a ). The charge-transfer reaction was the rate-determining step at lower fluoride concentrations of [F - ] ≤ 1 × 10 -3 M, leading to a high surface coverage of θ ss = 1, while the chemical dissolution reaction is the rate-determining step at higher fluoride concentrations of [F-] > 1 × 10 -3 M, leading to a decreased surface coverage of θ ss < 0.5.

Anodic oxygen evolution reaction on titanium oxide film and its affect on the surface and bulk properties of the film is an important subject in the Ti-based studies and applications. In this work, the behavior of oxygen evolution and some other related electrode processes occurring at anodically grown TiO 2 films on titanium were investigated within a relatively wide potential range by electrochemical measurements in 1 M perchloric acid solution. For the formation of the oxide film, three potential regions (two passive regions and the film breakdown region) were selected. The changes both in surface properties (mainly caused by oxygen evolution) and in bulk properties (mainly caused by increased potential) were taken into account for the observed different oxygen evolution behavior. The origin of a cathodic current peak at -0.2 V revealed in cyclic voltammograms was attributed to the reduction of the oxygen atoms adsorbed/absorbed at the oxide film surface, which were generated during anodic oxygen evolution. The flatband potential for the anodically formed titanium oxide films in 1.0 M HClO 4 was estimated as -0.2 V. With the semiconducting energy band structure models constructed for the Ti/oxide film/1 M HClO 4 electrode system, both the different behavior for anodic oxygen evolution on the titanium oxide films formed at different potentials and the electron transfer processes for the electrochemical reactions observed in this work were further interpreted.