The electrochemical formation and removal of thin oxide films on noble metals: Survey of some recent work—Evidence for a model involving high-field ion transport
✍ Scribed by M.J. Weaver
- Publisher
- Elsevier Science
- Year
- 1974
- Weight
- 900 KB
- Volume
- 51
- Category
- Article
- ISSN
- 0022-0728
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✦ Synopsis
The electrochemical formation and reduction of oxygen films on noble metals, particularly platinum, have been the subject of numerous studies 1. However, much confusion has surrounded attempts to obtain a general understanding of the behaviour of these systems. This can ,perhaps be traced to rather restrictiv e preconceptions of the possible surface structures and mechanisms involved; in particular the often-assumed dominance of simple chemisorbed oxygen species. Both conventional electrochemical and spectroscopic 2 techniques have been applied. The latter should provide valuable structural information, but studies of the former type yield the direct kinetic information required.
Recently, evidence has been presented 3-s for a rate-c°ntr°lling film growth process on platinum and gold substrates that involves an ion transport step under the influence of a high field, resulting in films consisting chiefly of in-cQrporated oxide. Very recently, however, evidence has appeared v-9 that strongly st~ggest that the initial film growth process, at least on platinum, is electrochemically reversible. It appears to involve more than one mode of chemisorptionl although an irreversible component is observed increasingly with high formation potentials and/or long formation times.
It will be demonstrated that these two very different conclusions can be completely compatible and indeed complementary to one another. A critical discussion of the ion transport model will also be presented, along with a discussion of its limitations and applicability to these extremely thin films. Suggestions will be made for experiments to provide a further diagnostic test of the model. Where relevant, the behaviour of analogous systems will be discussed. Although comparisons will be made between these, and other recent approaches, no attempt ~vill be made to provide a complete survey of even the recent, extensive literature concerned with noble metal-oxygen films. A study of a platinum oxygen film formed from a lithium chloride-potassium chloride melt containing oxide ig presented and discussed elsewhere 6.