Limits on the corrosion rate of Si surfaces in contact with CH3OH-ferrocene+/0 and CH3OH-1,1′-dimethylferrocene+/0 solutions

Gary A. Shreve, Chris D. Karp, Katherine E. Pomykal, Nathan S Lewis

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Although Si/CH3OH contacts have been extensively investigated and reported to provide highly efficient photoelectrochemical energy conversion devices, a recent study using the scanning electrochemical microscope (SECM) has claimed that, in CH3OH solutions, Si surfaces in contact with 4.57 mM ferrocenium (Fc+) were etched in the dark at a mass-transport-limited rate. The reported etching rate constant of >0.37 cm s-1 at 4.57 mM ferrocenium corresponds to an equivalent corrosion current density of >240 mA cm-2 and to a Si etch rate of >75 nm s-1. The presence of such severe corrosion was inferred from an unexpectedly large feedback current in an SECM experiment. The present work describes a search for corrosion of Si in contact with CH3OH-ferrocene+/0 and CH3OH-dimethylferrocene(Me2Fc)+/0 solutions through the use of very sensitive electrochemical, chemical, and physical methods. For CH3OH-1.0 M LiClO4-100 mM Me2Fc-80 mM Me2Fc+ solutions, an upper limit on the etch rate of 6.6 × 10-6 nm s-1 has been established through direct experimental measurements; thus, a 400 μm thick Si photoelectrode in contact with the CH3OH-Me2Fc+/0 electrolyte would require over 1500 years to corrode completely at room temperature. An alternative explanation for the SECM data, based on the documented existence of an inversion layer at the Si/liquid contact, is presented and shown to be consistent with the available data.

Original languageEnglish
Pages (from-to)5575-5580
Number of pages6
JournalJournal of Physical Chemistry
Issue number15
Publication statusPublished - 1995


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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