Microwave reflectance studies of photoelectrochemical kinetics at semiconductor electrodes. 2. Hydrogen evolution at p-Si in ammonium fluoride solution

Michael J. Cass, Noel W. Duffy, Laurence M. Peter, Stephen R. Pennock, Shin Ushiroda, Alison Walker

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Abstract

Microwave reflectance methods have been used to study the kinetics of photogeneration of hydrogen, on p-Si in acidic fluoride solutions. To estimate the rate constant for interfacial electron transfer, the magnitude of the observed steady-state light-induced microwave reflectivity change has been compared quantitatively with theoretical predictions based on numerical calculation of the electron and hole profiles in the silicon sample. In addition, the transient and periodic microwave reflectivity responses to stepped and sinusoidally modulated illumination, respectively, have been analyzed to obtain information about the electrode kinetics. The time constants for relaxation of the light-induced conductivity derived from this analysis confirm that electron transfer during hydrogen evolution is slow. The apparent inconsistency in the values of the phenomenological electron-transfer rate constants derived from the steady-state and transient or periodic responses can be resolved if it is assumed that hydrogen evolution proceeds via electron capture by protons followed by a slow bimolecular step leading to molecular hydrogen. Surface charging as the result of slow kinetics is expected to lead to band edge unpinning even at low light intensities, and the existence of this effect has been confirmed by transient photocapacitance measurements.
LanguageEnglish
Pages5864-5870
Number of pages7
JournalJournal of Physical Chemistry B
Volume107
Issue number24
DOIs
StatusPublished - 24 May 2003

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Microwaves
Semiconductor materials
Hydrogen
Electrodes
Kinetics
Electrons
Rate constants
Protons
Lighting
Silicon

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title = "Microwave reflectance studies of photoelectrochemical kinetics at semiconductor electrodes. 2. Hydrogen evolution at p-Si in ammonium fluoride solution",
abstract = "Microwave reflectance methods have been used to study the kinetics of photogeneration of hydrogen, on p-Si in acidic fluoride solutions. To estimate the rate constant for interfacial electron transfer, the magnitude of the observed steady-state light-induced microwave reflectivity change has been compared quantitatively with theoretical predictions based on numerical calculation of the electron and hole profiles in the silicon sample. In addition, the transient and periodic microwave reflectivity responses to stepped and sinusoidally modulated illumination, respectively, have been analyzed to obtain information about the electrode kinetics. The time constants for relaxation of the light-induced conductivity derived from this analysis confirm that electron transfer during hydrogen evolution is slow. The apparent inconsistency in the values of the phenomenological electron-transfer rate constants derived from the steady-state and transient or periodic responses can be resolved if it is assumed that hydrogen evolution proceeds via electron capture by protons followed by a slow bimolecular step leading to molecular hydrogen. Surface charging as the result of slow kinetics is expected to lead to band edge unpinning even at low light intensities, and the existence of this effect has been confirmed by transient photocapacitance measurements.",
author = "Cass, {Michael J.} and Duffy, {Noel W.} and Peter, {Laurence M.} and Pennock, {Stephen R.} and Shin Ushiroda and Alison Walker",
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T1 - Microwave reflectance studies of photoelectrochemical kinetics at semiconductor electrodes. 2. Hydrogen evolution at p-Si in ammonium fluoride solution

AU - Cass,Michael J.

AU - Duffy,Noel W.

AU - Peter,Laurence M.

AU - Pennock,Stephen R.

AU - Ushiroda,Shin

AU - Walker,Alison

N1 - ID number: ISI:000183592000029

PY - 2003/5/24

Y1 - 2003/5/24

N2 - Microwave reflectance methods have been used to study the kinetics of photogeneration of hydrogen, on p-Si in acidic fluoride solutions. To estimate the rate constant for interfacial electron transfer, the magnitude of the observed steady-state light-induced microwave reflectivity change has been compared quantitatively with theoretical predictions based on numerical calculation of the electron and hole profiles in the silicon sample. In addition, the transient and periodic microwave reflectivity responses to stepped and sinusoidally modulated illumination, respectively, have been analyzed to obtain information about the electrode kinetics. The time constants for relaxation of the light-induced conductivity derived from this analysis confirm that electron transfer during hydrogen evolution is slow. The apparent inconsistency in the values of the phenomenological electron-transfer rate constants derived from the steady-state and transient or periodic responses can be resolved if it is assumed that hydrogen evolution proceeds via electron capture by protons followed by a slow bimolecular step leading to molecular hydrogen. Surface charging as the result of slow kinetics is expected to lead to band edge unpinning even at low light intensities, and the existence of this effect has been confirmed by transient photocapacitance measurements.

AB - Microwave reflectance methods have been used to study the kinetics of photogeneration of hydrogen, on p-Si in acidic fluoride solutions. To estimate the rate constant for interfacial electron transfer, the magnitude of the observed steady-state light-induced microwave reflectivity change has been compared quantitatively with theoretical predictions based on numerical calculation of the electron and hole profiles in the silicon sample. In addition, the transient and periodic microwave reflectivity responses to stepped and sinusoidally modulated illumination, respectively, have been analyzed to obtain information about the electrode kinetics. The time constants for relaxation of the light-induced conductivity derived from this analysis confirm that electron transfer during hydrogen evolution is slow. The apparent inconsistency in the values of the phenomenological electron-transfer rate constants derived from the steady-state and transient or periodic responses can be resolved if it is assumed that hydrogen evolution proceeds via electron capture by protons followed by a slow bimolecular step leading to molecular hydrogen. Surface charging as the result of slow kinetics is expected to lead to band edge unpinning even at low light intensities, and the existence of this effect has been confirmed by transient photocapacitance measurements.

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JO - Journal of Physical Chemistry B

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SN - 1520-6106

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