The structure and composition of passive films electrochemically formed on Ni-Cr alloys in 1 M NaOH and 0.5 M H7S04 has been studied with x-ray photoelectron spectroscopy. The passivation potential was varied within the passive range up to the transpassive range and the time of passivation from 10 ms to 1000 s. With angular-resolved x-ray photoelectron spectroscopy, the passive film was found to have a two-layer structure with an inner oxide part formed directly at the metal surface and an outer hydroxide part in contact with the electrolyte. The metal surface underneath is enriched in Ni compared to the metal bulk composition. Except for potentials approaching the transpassive range, the hydroxide layer forms the dominant part of the passive film. Above 0.3 V in NaOH and 1.2 V in H2S04, Cr(VI) ions are found within the hydroxide layer. The maximum thickness of the passive layer is about 6 nm in NaOH and 3.5 nm in H2S04. The growth and the pronounced changes of the composition of the passive layers reflect the electrochemical behavior of the pure metal components. The results are in agreement with the thermodynamic data.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 35.8.191.249 Downloaded on 2015-03-29 to IP
A complete electrochemical oxidation-reduction cycle for a Cu monolayer on carbon-supported Pt clusters in alkaline solution has been monitored in situ by X-ray absorption spectroscopy. No desorption of Cu was observed upon oxidation. Near-range order and oxidation state of the Cu layer as a function of potential was obtained by in situ X-ray absorption spectroscopy. In contrast to bulk copper, the adsorbed copper monolayer transforms directly from the reduced state to Cu 2+ and from the oxidized form to Cu 0 . Adsorption of OHions on the Cu layer was observed for potentials below those for the Cu 0 f Cu 2+ and Cu 2+ f Cu 0 transitions.
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