Measurement of the dependence of interfacial charge-transfer rate constants on the reorganization energy of redox species at n-ZnO/H2O interfaces

Thomas W. Hamann, Florian Gstrein, Bruce S. Brunschwig, Nathan S Lewis

Research output: Contribution to journalArticle

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Abstract

The interfacial energetic and kinetics behavior of n-ZnO/H2O contacts have been determined for a series of compounds, cobalt trisbipyridine (Co(bpy)33+/2+), ruthenium pentaamine pyridine (Ru(NH 3)5py3+/2+), cobalt bis-1,4,7- trithiacyclononane (Co(TTCN)23+/2+), and osmium bis-dimethyl bipyridine bis-imidazole (Os(Me2bpy)2(lm) 23+/2+), which have similar formal reduction potentials yet which have reorganization energies that span approximately 1 eV. Differential capacitance vs potential and current density vs potential measurements were used to measure the interfacial electron-transfer rate constants for this series of one-electron outer-sphere redox couples. Each interface displayed a first-order dependence on the concentration of redox acceptor species and a first-order dependence on the concentration of electrons in the conduction band at the semiconductor surface, in accord with expectations for the ideal model of a semiconductor/liquid contact. Rate constants varied from 1 × 10-19 to 6 × 10-17 cm4 s-1. The interfacial electron-transfer rate constant decreased as the reorganization energy, λ, of the acceptor species increased, an a plot of the logarithm of the electron-transfer rate constant vs (λ + ΔG°′)2/4λkBT (where AG°′ is the driving force for interfacial charge transfer) was linear with a slope of ∼ -1. The rate constant at optimal exoergicity was found to be ∼5 × 10-17 cm4 s-1 for this system. These results show that interfacial electron-transfer rate constants at semiconductor electrodes are in good agreement with the predictions of a Marcus-type model of interfacial electron-transfer reactions.

Original languageEnglish
Pages (from-to)13949-13954
Number of pages6
JournalJournal of the American Chemical Society
Volume127
Issue number40
DOIs
Publication statusPublished - Oct 12 2005

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Oxidation-Reduction
Charge transfer
Rate constants
Electrons
Semiconductors
Semiconductor materials
Cobalt
Cobalt compounds
Osmium
Surface Tension
Ruthenium
Conduction bands
Pyridine
Contacts (fluid mechanics)
Electrodes
Current density
Capacitance
Kinetics
Liquids

ASJC Scopus subject areas

  • Chemistry(all)

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Measurement of the dependence of interfacial charge-transfer rate constants on the reorganization energy of redox species at n-ZnO/H2O interfaces. / Hamann, Thomas W.; Gstrein, Florian; Brunschwig, Bruce S.; Lewis, Nathan S.

In: Journal of the American Chemical Society, Vol. 127, No. 40, 12.10.2005, p. 13949-13954.

Research output: Contribution to journalArticle

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AB - The interfacial energetic and kinetics behavior of n-ZnO/H2O contacts have been determined for a series of compounds, cobalt trisbipyridine (Co(bpy)33+/2+), ruthenium pentaamine pyridine (Ru(NH 3)5py3+/2+), cobalt bis-1,4,7- trithiacyclononane (Co(TTCN)23+/2+), and osmium bis-dimethyl bipyridine bis-imidazole (Os(Me2bpy)2(lm) 23+/2+), which have similar formal reduction potentials yet which have reorganization energies that span approximately 1 eV. Differential capacitance vs potential and current density vs potential measurements were used to measure the interfacial electron-transfer rate constants for this series of one-electron outer-sphere redox couples. Each interface displayed a first-order dependence on the concentration of redox acceptor species and a first-order dependence on the concentration of electrons in the conduction band at the semiconductor surface, in accord with expectations for the ideal model of a semiconductor/liquid contact. Rate constants varied from 1 × 10-19 to 6 × 10-17 cm4 s-1. The interfacial electron-transfer rate constant decreased as the reorganization energy, λ, of the acceptor species increased, an a plot of the logarithm of the electron-transfer rate constant vs (λ + ΔG°′)2/4λkBT (where AG°′ is the driving force for interfacial charge transfer) was linear with a slope of ∼ -1. The rate constant at optimal exoergicity was found to be ∼5 × 10-17 cm4 s-1 for this system. These results show that interfacial electron-transfer rate constants at semiconductor electrodes are in good agreement with the predictions of a Marcus-type model of interfacial electron-transfer reactions.

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