Room temperature photoassisted formation of hydrogen-molybdenum bronzes with an alcohol as a hydrogen source

Pichat, Pierre; Can, Hoang Van; Van, Can Hoang

doi:10.1021/j100313a044

Cited by 48 publications

(31 citation statements)

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“…73,74 Thin films deposited on unheated substrates have an optical-absorption edge located between that of the single-phase ␣ and ␤ of MoO 3 -thin films. 4,55,75 The ␤ phase has a band gap of ϳ2.9 eV, [76][77][78] and the band range of 3.1-3.15 eV has been reported for ␣ phase. 76,79,80 The thermal energy of the Li x MoO 3 samples increases with temperature, and because of the phenomenal size in the number of phonons during the annealing process, the indirect band gap of Li x MoO 3 is ultimately shifted toward lower energy.…”

Section: Main Band Gap E O : Phonon Model For the Temperature-dependmentioning

confidence: 99%

Optical and electrochromic properties of annealed lithium-molybdenum-bronze thin films

Hussain

2002

Journal of Elec Materi

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Optical band gaps, Urbach inverse slopes, and coloration bands of various samples of annealed, microcrystalline Li x MoO 3 -bronze thin films in the concentration range 0 Ͻ x Ͻ 0.6 were determined over the photon energy range from 0.4 eV to 4.2 eV. On investigation, it is learned that the measured, optical band gaps do not shift rigidly over the annealing temperature range 293 Յ T Յ 423 K and, therefore, do not reveal the Burstein-Moss effect or reflect any stable, crystallographic phase transformation during any investigated annealing cycle. A model relating the temperature-dependent optical gap to the real part of the refractive index has also been developed, and this model fits very well to the annealed data within a maximum error of about 20%. Next, using an oscillator model, a phonon energy of ϳ0.08 eV was obtained, which is very close to the characteristic phonon energy of the material, MoO 3 . Using this model, it becomes more certain that the contributions to the Urbach absorption edge for the annealed-molybdenum bronzes are coming from the structural and compositional disorder. In another finding, it was found that the absorption-peak energy for the annealed data was about 1.5-1.6 eV, which is still broad and asymmetrical, and therefore, it is almost of the Mo 6ϩ (or Mo 4ϩ )-Mo 5ϩ intervalence or polaronic type. Using the polaron model, the half-bandwidth of the coloration bands of investigated, annealed Li x MoO 3 -thin films was found to be almost constant, which is consistent with the nonrigid band behavior.

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Section: Main Band Gap E O : Phonon Model For the Temperature-dependmentioning

confidence: 99%

Optical and electrochromic properties of annealed lithium-molybdenum-bronze thin films

Hussain

2002

Journal of Elec Materi

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“…We believe that the ammonium molecules at the surface decomposed to NH 3 gas and H + during laser irradiation. 34 The H + reacts with double-bonded terminal oxygen atoms in MoO 3 . The reaction produces hydroxyl groups (-OH) in the MoO 3 thin-lm as indicated in the As-coated 88% 12% 0% 91% 9% 72% 28% 120 88% 12% 0% 89% 11% 74% 26% 240 83% 17% 0% 86% 14% 83% 17% 400 79% 21% 0% 81% 19% 87% 13% 600 68% 21% 11% 67% 33% 91% 9% Thermal annealing 92% 8% 0% 91% 9% 81% O1s XPS spectra (Fig.…”

Section: Reduction Mechanism and Chemical Compositionmentioning

confidence: 99%

Ultrafast laser-assisted synthesis of hydrogenated molybdenum oxides for flexible organic solar cells

et al. 2016

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A novel method to synthesize a hydrogenated molybdenum oxide (H y MoO 3Àx ) thin film by irradiation of photons using a KrF laser (l ¼ 248 nm) on an ammonium heptamolybdate ((NH 4 ) 6 Mo 7 O 24 $4H 2 O) precursor layer is demonstrated. The laser-assisted synthesis is simple, and can be conducted in an ambient atmosphere without damaging the underlying bottom electrode and plastic substrate. The exposure time (30 ns) is extremely short compared to thermal annealing (>3 min). Because the highenergy photons are absorbed by the MoO 3 layer and provide the activation energy for the reaction, the hydrogen atoms that dissociate from the ammonium molecules bond to the MoO 3 ; this process yields a H y MoO 3Àx thin-film. By controlling the laser energy, the stoichiometry of the H y MoO 3Àx layer can be manipulated to simultaneously obtain advantageous electrical properties of both high work function (5.6 eV) and electrical conductivity (9.9 mS cm À1). The H y MoO 3Àx hole transport layer (HTL) is successfully demonstrated on flexible top-illuminated PTB7:PCBM organic solar cells (OSCs). This OSC has good mechanical flexibility, and 75% higher short-circuit current than the device with a PEDOT:PSS HTL.Finite-domain time-difference simulations were conducted to verify the enhancement of the photocurrent. The thin layer of H y MoO 3Àx was proven to be suitable for the microcavity condition which allows a resonant wavelength match to the PTB7:PCBM active layer.

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“…The illumination in the near UV of a suspended mixture of MoO 3 and TiO 2 in isopropanol in the absence of air produces the formation of a hydrogenmolybdenum bronze H 0.93 MoO 3 [14]. TiO 2 acts as a dehydrogenation photocatalyst, which necessitates a metal co-catalyst for dihydrogen recombination and evolution (see above).…”

Section: Photo-assisted Preparation Of H X Moo 3 Hydrogen Bronzementioning

confidence: 99%

From catalysis by metals to bifunctional photocatalysis

Herrmann

2006

Top Catal

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Catalysis by metals'', was transposed to ''Bifunctional Photocatalysis'', based on noble metals deposited on titania. Both, participation (i) of the photo-active oxidic support and (ii) of the deposited metal have been successfully analyzed, delimited and associated. For both reactions involving hydrogen (Cyclopentane-Deuterium Isotope Exchange (CDIE) and alcohol dehydrogenation), the respective roles of electrons and holes were clearly put in evidence. The photogenerated electrons were found to be spontaneously transferred to the metal nano-particles because of the alignment of the Fermi levels of both solid phases. They neutralize protons H + (or deuterons D + ) into atoms before their recombination and evolution of dihydrogen (or HD). Simultaneously, photogenerated holes h + neutralize anionic species in oxidation reactions responsible for the activation of organic molecules. These two anionic species were OD ) deuteroxyl surface groups in CDIE and alcoholate anions RO ) in alcohol dehydrogenation, respectively. Both reactions exhibited a stoichiometric threshold which was exceeded several hundreds of times, clearly defining the real catalytic character of both reactions. The titania-deposited noble metals appeared as auxiliaries or co-catalysts working independently of UV-irradiation for making the reaction run catalytically. Eventually, the concepts of bifunctional photocatalysis were applied to account for interphasic photocatalytic processes such as hydrogen transfer, electron transfer, photosensitization in the visible via CdS addition.

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Room temperature photoassisted formation of hydrogen-molybdenum bronzes with an alcohol as a hydrogen source

Cited by 48 publications

References 1 publication

Optical and electrochromic properties of annealed lithium-molybdenum-bronze thin films

Optical and electrochromic properties of annealed lithium-molybdenum-bronze thin films

Ultrafast laser-assisted synthesis of hydrogenated molybdenum oxides for flexible organic solar cells

From catalysis by metals to bifunctional photocatalysis

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