Measurement of the driving force dependence of interfacial charge-transfer rate constants in response to pH changes at n-ZnO/H2O interfaces

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

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

Changes in pH have been used to shift the band-edge positions of n-type ZnO electrodes relative to solution-based electron acceptors having pH-independent redox potentials. Differential capacitance vs. potential and current density vs. potential measurements using [Co(bpy)3]3+/2+ and [Ru(bpy)2(MeIm)2]3+/2+ (where bpy = 2,2′-bipyridyl and MeIm = 1-methyl-imidazole) allowed investigation of the pH-induced driving-force dependence of the interfacial electron-transfer rate in the normal and inverted regions of electron transfer, respectively. All rate processes were observed to be kinetically first-order in the concentration of electrons at the ZnO surface and first-order in the concentration of dissolved redox acceptors. Measurements using [Co(bpy)3]3+/2+, which has a low driving force and a high reorganization energy in contact with ZnO electrodes, and measurements of [Ru(bpy)2(MeIm)2]3+/2+, which has a high driving force and a low reorganization energy in contact with ZnO electrodes, allowed for the evaluation of both the normal and inverted regions of interfacial electron-transfer processes, respectively. The rate constant at optimum exoergicity was observed to be approximately 5 × 10-17 cm4 s-1. The rate constant vs. driving-force dependence at n-type ZnO electrodes exhibited both normal and inverted regions, and the data were well-fitted by parabolas generated using classical electron-transfer theory.

Original languageEnglish
Pages (from-to)15-23
Number of pages9
JournalChemical Physics
Volume326
Issue number1
DOIs
Publication statusPublished - Jul 11 2006

Fingerprint

Charge transfer
Rate constants
electron transfer
charge transfer
electrodes
Electrons
Electrodes
parabolas
imidazoles
2,2'-Dipyridyl
electrons
capacitance
current density
energy
evaluation
shift
Capacitance
Current density
Oxidation-Reduction
tris(2,2'-bipyridyl)cobalt(III)

Keywords

  • Electron transfer
  • pH
  • Semiconductor
  • ZnO

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Spectroscopy
  • Atomic and Molecular Physics, and Optics

Cite this

Measurement of the driving force dependence of interfacial charge-transfer rate constants in response to pH changes at n-ZnO/H2O interfaces. / Hamann, Thomas W.; Gstrein, Florian; Brunschwig, Bruce S.; Lewis, Nathan S.

In: Chemical Physics, Vol. 326, No. 1, 11.07.2006, p. 15-23.

Research output: Contribution to journalArticle

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