Titanium alloy electrodes are widely employed as both cathodes and anodic substrates.  The superior corrosion resistance and low density of titanium makes it a useful material for industrial applications. In oxygen containing environments such as air or water, a thin titania layer spontaneously forms on bare titanium surfaces. Historically, the operative surface states of titanium have been termed: active [essentially metallic], transitional, and passive [comprising a titania over-layer]. In this project, the electrochemical response of a titanium electrode in contact with aqueous tetrafluoroborate solution [or in contact with aqueous formate solution] was monitored to tentatively identify the surface states.

Tetrafluoroboric acid is strongly ionizable in water and resultant HBF₄ solutions are able to oxidize various metals. Starting with either HBF₄ or KBF₄, the electrochemical response of a titanium disk electrode in contact with aqueous tetrafluoroborate solutions [sparged with argon gas] was recorded. Cyclic voltammograms of 0.1 molar HBF₄ on titanium, without additional electrolyte, showed two cathodic features near -0.51 V and -0.95 V versus Ag-AgCl electrode [see figure below]. The more negative feature is posited to correspond to active state titanium with H₂ evolution. Scan reversal near -0.95 V to the positive direction promptly generates a prominent anodic peak near -0.65 V though the post-peak current remains anodic and rather steady out to +2.0 V. The prominent anodic peak may correspond to dissolution of titanium metal. Interestingly, the shapes of the cyclic voltammograms of aqueous KBF₄  solutions were experimentally determined to be pH dependent.

By contrast, formic acid is weakly ionizable in aqueous solutions. Cyclic voltammograms of 3.5 molar HCO₂H solutions on titanium showed a cathodic feature near -0.87 V that may correspond to active state titanium and, upon positive direction scanning, an anodic feature that starts near -0.25 V and plateaus after +0.2 V. The anodic plateau is posited to correspond to passive state titanium. Cycling between about +0.55 V and -1.0 V led to a detectable negative potential shift in the H₂ evolution reaction [possibly due to titania formation during positive scanning]. At the similar hydrogen ion condition of pH 1, cyclic voltammograms of aqueous HCO₂H and HBF₄ were different:  the prominent anodic peak was not observed for formic acid.