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Title: Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics

Abstract

Two sensitizers, [Ru(bpy) 2 (dcb)] 2+ ( RuC ) and [Ru(bpy) 2 (dpb)] 2+ ( RuP ), were anchored to mesoporous TiO 2 thin films and utilized to sensitize the reaction of TiO 2 electrons with oxidized triphenylamines to visible light in CH 3 CN electrolytes.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, USA
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1411100
Grant/Contract Number:
SC0013461
Resource Type:
Journal Article: Published Article
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 9; Journal Issue: 4; Related Information: CHORUS Timestamp: 2018-01-24 09:44:59; Journal ID: ISSN 2041-6520
Publisher:
Royal Society of Chemistry (RSC)
Country of Publication:
United Kingdom
Language:
English

Citation Formats

DiMarco, Brian N., Troian-Gautier, Ludovic, Sampaio, Renato N., and Meyer, Gerald J. Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics. United Kingdom: N. p., 2018. Web. doi:10.1039/C7SC03839A.
DiMarco, Brian N., Troian-Gautier, Ludovic, Sampaio, Renato N., & Meyer, Gerald J. Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics. United Kingdom. doi:10.1039/C7SC03839A.
DiMarco, Brian N., Troian-Gautier, Ludovic, Sampaio, Renato N., and Meyer, Gerald J. Mon . "Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics". United Kingdom. doi:10.1039/C7SC03839A.
@article{osti_1411100,
title = {Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics},
author = {DiMarco, Brian N. and Troian-Gautier, Ludovic and Sampaio, Renato N. and Meyer, Gerald J.},
abstractNote = {Two sensitizers, [Ru(bpy) 2 (dcb)] 2+ ( RuC ) and [Ru(bpy) 2 (dpb)] 2+ ( RuP ), were anchored to mesoporous TiO 2 thin films and utilized to sensitize the reaction of TiO 2 electrons with oxidized triphenylamines to visible light in CH 3 CN electrolytes.},
doi = {10.1039/C7SC03839A},
journal = {Chemical Science},
number = 4,
volume = 9,
place = {United Kingdom},
year = {Mon Jan 01 00:00:00 EST 2018},
month = {Mon Jan 01 00:00:00 EST 2018}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1039/C7SC03839A

Citation Metrics:
Cited by: 1work
Citation information provided by
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  • Nanosecond laser flash photolysis and photocurrent measurements have been used to investigate use of [Ru(bpy) 2((4,4'-PO 3H 2) 2bpy)] 2+ attached to TiO 2 nanoparticle films, TiO 2-Ru II, in a dye-sensitized photoelectrosynthesis cell (DSPEC) configuration for H 2 production. In these experiments, laser flash excitation of TiO 2-Ru II and rapid injection lead to TiO 2(e -)-Ru III with subsequent TiO 2(e -)-Ru III → TiO 2-Ru II back electron transfer monitored on the nsec time scale with and without added triethanolamine (TEOA) and deprotonated ethylenediaminetetraacetic tetra-anion (EDTA 4-) as irreversible electron transfer donors. With added TEOA or EDTAmore » 4-, a competition exists between back electron transfer and scavenger oxidation with the latter leading to H 2 production in the photoelectrosynthesis cell. Reduction of TiO 2(e -)-Ru III by both TEOA and EDTA 4- occurs with k D ~ 10 6 M -1 s -1. EDTA 4- is a more efficient scavenger by a factor of ~3 because of a more favorable partition equilibrium between the film and the external solution. Its increased scavenger efficiency appears in incident photon-to-current conversion efficiency (IPCE) measurements, in electron collection efficiencies (η coll), and in photocurrent measurements with H 2 production. Evaluation of electron collection efficiencies by transient current measurements gave η coll ~ 24% for TEOA and ~ 70% for EDTA 4-. The dynamics of back electron transfer are minimized, and collection efficiencies, photocurrents, and hydrogen production are maximized by application of a positive applied bias consistent with the results of I-V measurements. A pH dependent plateau is reached at ~0 V at pH = 4.5 (EDTA 4-) and at ~ -0.4 V at pH 6.7 (TEOA). The difference is qualitatively consistent with the influence of pH on electron population in trap states below the conduction band and the role they play in back electron transfer. The excitation dependence of IPCE measurements matches the spectrum of TiO 2-Ru II with IPCE values ~3 times higher for EDTA 4- than for TEOA as noted above. Absorbed photon-to-current efficiency (APCE) values are light-intensity dependent because of the effect of multiple injection events and the influence of increasing trap site electron densities on back electron transfer. The key to efficient H 2 production is minimizing back electron transfer. Application of a sufficiently positive potential relative to E CB for TiO 2 accelerates loss of electrons from the film in competition with back electron transfer allowing for H 2 production with efficiencies approaching 14.7% under steady-state irradiation.« less
  • Nanosecond laser flash photolysis and photocurrent measurements have been used to investigate use of [(Ru(bpy)2(4,4'-(PO3H2)2bpy)]2+ attached to TiO2 nanoparticle films, TiO2-RuII, in a dye-sensitized photoelectrosynthesis cell (DSPEC) configuration for H2 production. In these experiments, laser flash excitation of TiO2-RuII and rapid injection lead to TiO2(e-)-RuIII with subsequent TiO2(e-)-RuIII → TiO2-RuII back electron transfer monitored on the nsec time scale with and without added triethanolamine (TEOA) and deprotonated ethylenediaminetetraacetic tetra-anion (EDTA4-) as irreversible electron transfer donors. With added TEOA or EDTA4-, a competition exists between back electron transfer and scavenger oxidation with the latter leading to H2 production in the photoelectrosynthesismore » cell. Reduction of TiO2(e-)-RuIII by both TEOA and EDTA4- occurs with kD ~ 106 M-1 s-1. EDTA4- is a more efficient scavenger by a factor of ~3 because of a more favorable partition equilibrium between the film and the external solution. Its increased scavenger efficiency appears in incident photon-to-current conversion efficiency (IPCE) measurements, in electron collection efficiencies (ηcoll), and in photocurrent measurements with H2 production. Evaluation of electron collection efficiencies by transient current measurements gave ηcoll ~ 24% for TEOA and ~ 70% for EDTA4-. The dynamics of back electron transfer are minimized, and collection efficiencies, photocurrents, and hydrogen production are maximized by application of a positive applied bias consistent with the results of I-V measurements. A pH dependent plateau is reached at ~0 V at pH = 4.5 (EDTA4-) and at ~ -0.4 V at pH 6.7 (TEOA). The difference is qualitatively consistent with the influence of pH on electron population in trap states below the conduction band and the role they play in back electron transfer. The excitation dependence of IPCE measurements matches the spectrum of TiO2-RuII with IPCE values ~3 times higher for EDTA4- than for TEOA as noted above. Absorbed photon-to-current efficiency (APCE) values are light-intensity dependent because of the effect of multiple injection events and the influence of increasing trap site electron densities on back electron transfer. The key to efficient H2 production is minimizing back electron transfer. Application of a sufficiently positive potential relative to ECB for TiO2 accelerates loss of electrons from the film in competition with back electron transfer allowing for H2 production with efficiencies approaching 14.7% under steady-state irradiation.« less
  • Analytical expressions describing electron transport in dye-sensitized nanocrystalline TiO{sub 2} solar cells are derived and verified by intensity-modulated photocurrent spectroscopy measurements. An exponential distribution of surface states can account for the observed power law dependence of the electron-transport rate on the electron population. Use of an effective electron diffusion coefficient to describe the electron transport kinetics is found to be inadequate. A slope of 69 MeV is inferred for the surface-state distribution curve.
  • The optical and electronic properties of dye aggregates of p-methyl red on a TiO2 anatase (101) surface were modeled as a function of aggregation order (monomer to pentameric dye) via first principles calculations. A progressive red-shifting and intensity increase toward the visible region in UV/vis absorption spectra is observed from monomeric-to-tetrameric dyes, with each molecule in a given aggregate binding to one of the four possible TiO2 (101) adsorption sites. The pentamer exhibits a blue-shifted peak wave- length in the UV/vis absorption spectra and less absorption intensity in the visible region in comparison; a corresponding manifestation of H-aggregation occurs sincemore » one of these five molecules cannot occupy an adsorption site. This finding is consistent with experiment. Calculated density of states (DOS) and partial DOS spectra reveal similar dye…TiO2 nanocomposite conduction band characteristics but different valence band features. Associated molecular orbital distributions reveal dye-to-TiO2 interfacial charge transfer in all five differing aggregate orders; meanwhile, the level of intramolecular charge transfer in the dye becomes progressively localized around its azo- and electron-donating groups, up to the tetrameric dye/TiO2 species. Dye adsorption energies and dye coverage levels are calculated and compared with experiment. Overall, the findings of this case study serve to aid the molecular design of azo dyes towards better performing DSSC devices wherein they are incorporated. In addition, they provide a helpful example reference for understanding the effects of dye aggregation on the adsorbate…TiO2 interfacial optical and electronic properties.« less