Generation of Highly n-Type Titanium Oxide Using Plasma Fluorine Insertion

Seo, Hyungtak; Baker, L. Robert; Hervier, Antoine; Kim, Jin-Woo; Whitten, J. L.; Somorjai, Gábor A.

doi:10.1021/nl1039378

Cited by 86 publications

(96 citation statements)

References 20 publications

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“…Note that, our results are in full agreement with the passivation and n-type doping effect of SF 6 plasma on TiO 2 recently demonstrated by H. Seo and co-workers. 84 These results demonstrate that fluorine passivation of ZnO films using not only plasma, but potentially also other methods, e.g. the incorporation of fluorine dopant in the precursor solution, may be promising for making high-performing PSCs but also for photonics and various optoelectronic applications.…”

Section: Influence Of Fluorine Plasma Treatment Of Zno Onmentioning

confidence: 86%

Surface passivation effect by fluorine plasma treatment on ZnO for efficiency and lifetime improvement of inverted polymer solar cells

et al. 2016

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Section: Influence Of Fluorine Plasma Treatment Of Zno Onmentioning

confidence: 86%

Surface passivation effect by fluorine plasma treatment on ZnO for efficiency and lifetime improvement of inverted polymer solar cells

et al. 2016

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“…The research presented here shows that similar electronic O activation also occurs by electron spillover from a highly n-type catalyst support. 39,76,77 These results demonstrate the electronic nature of SMSI as well as the utility of metal-support interactions to electronically control the activity and selectivity of oxidation catalysts. In this work, it is also shown that non-thermal control of catalytic surface chemistry is possible by externally controlling the electronic structure at a metal-support interface using a solid-state charge-based device.…”

Section: Mechanisms Of Smsimentioning

confidence: 83%

“…By these combined effects, F doping allows fabrication of titanium oxide films with a high Fermi energy and an electron transport channel in the true conduction band, and these effects on the electronic structure of titanium oxide have been published in Nano Letters. 76 Chapters 6 and 7 show that supporting Pt catalysts on F-doped titanium oxide results in electronically mediated catalytic activity for CO oxidation and methanol oxidation. In the case of CO oxidation, electron density from the highly n-type support appears to activate surface O, resulting in an approximately two-fold increase in catalytic activity.…”

Section: Fluorine-doped Titanium Oxide As An Electronically Active Plmentioning

confidence: 99%

Charge Transfer and Catalysis at the Metal Support Interface

Baker

2012

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Kinetic, electronic, and spectroscopic characterization of model Pt-support systems are used to demonstrate the relationship between charge transfer and catalytic activity and selectivity. The results show that charge flow controls the activity and selectivity of supported metal catalysts.Using a Pt/n-Si Schottky junction, it is possible to externally control the electronic properties at the Pt/Si interface by applying bias or by exciting charge carriers with visible light. It is found that this device can control the rate of CO oxidation on Pt. Results show that negative charge on the Pt increases the reaction rate while positive charge on the Pt decreases the reaction rate. This is the first time that a solid-state device has been used to externally control the rate of a chemical reaction as determined by directly measuring the product yield. Similar experiments were performed for the H 2 oxidation reaction and analogous results were obtained.Similarly, electronic control of catalyst performance can be achieved by substrate doping. It is shown that F doping can tune the electronic structure of TiO 2 . When F is incorporated into TiO 2 , the electrical conductivity is dramatically enhanced because F acts as an n-type dopant. It is shown that this highly n-type TiO 2 acts as an electronically active support for Pt catalysts, increasing the rate of CO oxidation by electronically activating surface O. It is further shown that for a multipath reaction, the electronic structure of TiO 2 also controls the reaction selectivity. The electronic activity of highly n-type TiO 2 serving as a Pt support for methanol oxidation selectively enhances the production of formaldehyde relative to CO 2 .Finally, sum frequency generation (SFG) vibrational spectroscopy is used to probe the molecular nature of strong metal-support interactions (SMSI). This is the first time that SFG has been used to probe the highly selective oxide-metal interface during catalytic reaction, and the results demonstrate that charge transfer from TiO 2 on a Pt/TiO 2 catalyst controls the product distribution of furfuraldehyde hydrogenation by an acid-base mechanism. SFG spectra reveal that a furfuryl-oxy intermediate forms on TiO 2 as a result of a charge transfer interaction. This furfuryl-oxy intermediate is a highly active and selective precursor to furfuryl alcohol, and spectral analysis shows that the Pt/TiO 2 interface is required primarily for H spillover. Density functional calculations predict that O-vacancies on the TiO 2 surface activate the formation of the furfuryl-oxy intermediate via an electron transfer to furfuraldehyde, drawing a strong analogy between SMSI and acid-base catalysis. 2This dissertation builds on extensive existing knowledge of metal-support interactions in heterogeneous catalysis. The results show the prominent role of charge transfer at catalytic interfaces to determine catalytic activity and selectivity. Further, this research demonstrates the possibility of selectively driving catalytic chemistry by controlling charge f...

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“…35 They found that following a reduction treatment at temperature of 773 K or above the adsorption of H2 and CO dropped nearly to zero indicating the available metal surface area vanished, while the total surface area of the catalyst remained unchanged. This effect was termed the strong metal-support interaction (SMSI).…”

Section: Support Effects In Catalysismentioning

confidence: 99%

“…It is well known that in TiO2, O-vacancies act as electron donors into mid-gap states of the reduced oxide which results in a greatly enhanced surface conductivity. 35 Because the nonresonant contribution to an SFG spectrum is largely the result of free electron motion at the surface of the substrate, it is not surprising that increased TiO2 conductivity by H2 reduction results in a dramatic enhancement of the nonresonant signal. This effect is reversible in O2 as shown in Figure 4.6.…”

Section: Probing Reaction Intermediates By Sfg Vibrational Spectroscopymentioning

confidence: 99%

Support effects in catalysis studied by in-situ sum frequency generation vibrational spectroscopy and in-situ x-ray spectroscopies

Kennedy

2017

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Kinetic measurements are paired with in-situ spectroscopic characterization tools to investigate colloidally based, supported Pt catalytic model systems in order to elucidate the mechanisms by which metal and support work in tandem to dictate activity and selectivity. The results demonstrate oxide support materials, while inactive in absence of Pt nanoparticles, possess unique active sites for the selective conversion of gas phase molecules when paired with an active metal catalyst.In order to establish a paradigm for metal-support interactions using colloidally synthesized Pt nanoparticles the ability of the organic capping agent to inhibit reactivity and interaction with the support must first be assessed. Pt nanoparticles capped by poly(vinylpyrrolidone) (PVP), and those from which the PVP is removed by UV light exposure, are investigated for two reactions, the hydrogenation of ethylene and the oxidation of methanol. It is shown that prior to PVP removal the particles are moderately active for both reactions. Following removal, the activity for the two reactions diverges, the ethylene hydrogenation rate increases 10-fold, while the methanol oxidation rate decreases 3-fold. To better understand this effect the capping agent prior to, and the residual carbon remaining after UV treatment are probed by sum frequency generation vibrational spectroscopy. Prior to removal no major differences are observed when the particles are exposed to alternating H2 and O2 environments. When the PVP is removed, carbonaceous fragments remain on the surface that dynamically restructure in H2 and O2. These fragments create a tightly bound shell in an oxygen environment and a porous coating of hydrogenated carbon in the hydrogen environment. This observation explains the divergent catalytic results. Reaction rate measurements of thermally cleaned PVP and oleic acid capped particles show this effect to be independent of cleaning method or capping agent. In all this demonstrates the ability of the capping agent to mediate nanoparticle catalysis.With this established the hydrogenation of furfural by Pt supported on SiO2 and TiO2 was investigated by an approach combining reaction studies with SFG in order to gain molecular level insight into the nature of the metal-support interaction. This is the first instance of SFG being 2 used to probe the factors governing selectivity in a supported catalyst system. This work revealed that TiO2 possessed sites, that while inactive without Pt, became highly active for the selective conversion of furfural to furfuryl alcohol. By SFG a TiO2 bound intermediate species was identified that could explain the highly selective nature of the reaction by Pt/TiO2. In combination with density functional theory calculations it was determined that furfural bound favorably to oxygen vacancy sites on the TiO2 surface through the aldehyde oxygen, which in turn activated the aldehyde group for hydrogenation by a charge transfer mechanism. This intermediate could then react with spillover hydrogen from the Pt surface...

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Generation of Highly n-Type Titanium Oxide Using Plasma Fluorine Insertion

Cited by 86 publications

References 20 publications

Surface passivation effect by fluorine plasma treatment on ZnO for efficiency and lifetime improvement of inverted polymer solar cells

Surface passivation effect by fluorine plasma treatment on ZnO for efficiency and lifetime improvement of inverted polymer solar cells

Charge Transfer and Catalysis at the Metal Support Interface

Support effects in catalysis studied by in-situ sum frequency generation vibrational spectroscopy and in-situ x-ray spectroscopies

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