A channel flow triple electrode (CFTE) was employed for the in-situ detection of Fe2+ and Fe3+ preferentially dissolved from a Pt–50at.%Fe alloy under potential cycles in a 0.5 M H2SO4 solution. The CFTE consisted of a Pt–50at.%Fe alloy working electrode (PtFe-WE) and two split Au collector electrodes (Au–CE) placed upstream and downstream in a channel, respectively. The optimum potentials for detecting Fe2+ and Fe3+ on the Au–CEs were determined to be 1.0 and 0 V vs. a standard hydrogen electrode, respectively, when using solutions of different concentrations of FeSO4 and Fe2(SO4)3. When PtFe–WE was potential-cycled between 0.05 and 1.4 V, Fe dissolved as Fe2+ between 0.25 and 0.75 V in both anodic and cathodic scans, and mainly dissolved as Fe3+ above 1.1 V and from 0.9 to 0.5 V in cathodic scans.

The selective dissolution of cobalt and the consequent surface enrichment of platinum in PtCo binary alloys immersed in 0. ) exhibited more extensive selective dissolution and roughened surfaces. In this study, the selective dissolution and surface morphology of the PtCo alloys are discussed on the basis of these experimental results.

A channel flow triple electrode (CFTE) was applied for the in situ detection of Fe ions (Fe(II) and Fe(III)) and Pt ions (Pt(II) and Pt(IV)) dissolved from Pt-50at%Fe (Pt-50Fe) and Pt-25at%Fe (Pt-25Fe), under potential cycling in 0.5 M H 2 SO 4 at 298 K. These ions, dissolved from a Pt-Fe alloy working electrode set upstream in a channel, were simultaneously detected on two Au collector electrodes placed downstream by reducing or oxidizing their dissolved ions. When Pt-50Fe was potential-cycled between 0.05 and 1.4 V vs. standard hydrogen electrode, Fe dissolution was significantly enhanced in a double-layer (DL) charging region (0.25-0.85 V), probably owing to the surface diffusion of Pt atoms. In addition, the Fe dissolution was enhanced by Pt dissolution which takes place in a place-exchange potential region (1.2-1.4 V) and in the reduction potential of Pt oxides (0.9-0.5 V) in the cathodic scan. On the contrary, when Pt-25Fe was potential-cycled between 0.05 and 1.4 V, Fe dissolution was strongly suppressed by a Pt-enriched layer, especially in the potential region for the DL. The dissolution also depended on the upper limit of potential cycling (E U

Zinc corrosion under 0.2 M NaCl solution films 5-800 μm in thickness was studied by electrochemical impedance spectroscopy (EIS). As-polished and rusted zinc plates obtained by exposure to a natural atmospheric environment for 1, 3, 6, and 12 months were used as working electrodes. The obtained EIS results were analyzed using a transmission line equivalent circuit to determine the charge transfer resistance (R ct ), the reciprocal of which is proportional to the corrosion current density. For the as-polished zinc, the corrosion behavior is divided into three regions by the solution film thickness (X f ). In Region I (X f : 800-200 μm), R ct −1 is independent of X f and is approximately ten times smaller than that for carbon steel. In Region II (X f : 200-25 μm), however, R ct −1 increases with decreasing solution thickness down to approximately 25 μm due to an enhancement of the oxygen diffusion (cathodic process) through the solution film. In Region III (X f < 25 μm), further decreases in thickness reduce R ct −1 because the zinc dissolution (anodic process) is suppressed. In contrast, R ct −1 of the rusted zinc is independent of X f because the charge transfer process is strongly suppressed by the zinc corrosion products, which were identified as simonkolleite and zinc oxide.

Galvanic corrosion of 6061-T6 (AA) coupled with high-strength steel (HSS) under 2 M NaCl solution films was investigated by electrochemical impedance spectroscopy (EIS). The AA is passivated in a 2 M NaCl solution and suffered pitting corrosion by galvanic coupling with HSS of the same surface area. Impedance of the AA/HSS couple was successfully measured under thin solution films (25-100 μm) using a potentiostat as a zero-resistance ammeter. The obtained impedance data shows a typical transmission line behavior above 1 kHz, owing to a nonuniform current distribution. Impedances for the AA and HSS were separately measured in the frequency domain. The average growth rate of pits on the AA surface, estimated from the charge transfer resistance for AA, increased with decreasing solution film thickness.