Stability of n-Si/CH3OH contacts as a function of the reorganization energy of the electron donor

Katherine E. Pomykal, Arnel M. Fajardo, Nathan S Lewis

Research output: Contribution to journalArticle

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Abstract

Predictions of the Marcus/Gerischer theory for photoelectrode stability have been investigated experimentally for n-Si/CH3OH photoelectrochemical cells. Specifically, a semiconductor electrode is predicted to be more stable if the reorganization energy of the stabilizing agent is decreased (in the normal region of the Marcus behavior), thereby increasing the rate of minority carrier capture by the stabilizer. This prediction was quantified experimentally by monitoring the branching ratio between two competing reactions at a semiconductor/liquid interface: hole transfer from a Si photoanode to the electron donor in solution vs passivation of the Si photoanode through hole transfer to water. Deliberate addition of water to n-Si/CH3OH contacts provided a constant, known passivation pathway that competed with charge transfer to the stabilizing agent. Dimethylferrocene (Me2Fc), ruthenium(II) pentaammine 4,4′-bipyridine (Ru(NH3)5(4,4′-bpy)2+), and cobalt(II) tris-(2,2′-bipyridine) (Co(2,2′-bpy)3 2+) provided three outer sphere electron donors with very similar standard electrochemical potentials but varying solvent reorganization energies. At constant electron donor concentration, constant driving force for reaction, constant photocurrent density, and constant water concentration in CH3-OH, the stability of n-Si photoelectrodes decreased in the order Me2Fc+/0 > Ru(NH3)5(4,4′-bpy)3+/2+ > Co-(2,2′-bpy)3 3+/2+. This observation can be consistently explained through the theoretically predicted influence of the minority carrier acceptor reorganization energy on the interfacial charge transfer rate constant.

Original languageEnglish
Pages (from-to)8302-8310
Number of pages9
JournalJournal of Physical Chemistry
Volume99
Issue number20
Publication statusPublished - 1995

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Excipients
Passivation
Electrons
Water
Charge transfer
Rate constants
Semiconductor materials
Photoelectrochemical cells
electrons
Ruthenium
Cobalt
minority carriers
Photocurrents
passivity
energy
charge transfer
water
Electrodes
Monitoring
Liquids

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Stability of n-Si/CH3OH contacts as a function of the reorganization energy of the electron donor. / Pomykal, Katherine E.; Fajardo, Arnel M.; Lewis, Nathan S.

In: Journal of Physical Chemistry, Vol. 99, No. 20, 1995, p. 8302-8310.

Research output: Contribution to journalArticle

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