Magnetic susceptibility and thermoelectric power of tungsten intermediary oxides

Polaczek, A.; Pękała, M.; Obuszko, Z.

doi:10.1088/0953-8984/6/39/011

Cited by 42 publications

(31 citation statements)

References 33 publications

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“…To determine if a change of carrier concentration is responsible for the improved photocurrent, 10,47,48 Mott-Schottky plots were recorded for the same WO 3 film before and after reduction ( Figure 5A). Positive slopes are seen in both cases, as expected for n-type WO 3 .…”

Section: Resultsmentioning

confidence: 99%

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Zhao

Olide

Osterloh

2014

J. Electrochem. Soc.

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Here we report an electrochemical reduction-induced photocurrent enhancement up to an order of magnitude for monoclinic tungsten trioxide (WO 3 ) particulate photoanodes. Electrochemical impedance and photoelectrochemical measurements suggest that the improved performance is attributed to the increase in majority carrier concentration (from 1.5 × 10 18 to 2.5 × 10 21 cm −3 ). This results in higher conductivity and improved electron transport. Minority carrier extraction can be increased by reducing the WO 3 particle size from 200 nm to 50 and 30 nm. The larger solid-liquid interface area promotes the water oxidation rate. By balancing electron/hole extraction with photon absorption in an optimized 30 nm WO 3 particulate electrode, a record water oxidation photocurrent of 3.8 mA/cm 2 , under +1.36 V (vs. RHE) applied bias in 0.1 M Na 2 SO 4 solution at pH = 3.5 is achieved with 50 mW/cm 2 unfiltered Xe illumination. Photoelectrochemical water splitting is an efficient way of converting solar energy to chemical fuel by decomposing water into hydrogen and oxygen.1-9 Among inorganic materials that catalyze the photoelectrolysis of water, WO 3 with a bandgap of 2.6 eV is attractive due to its visible absorption and its photochemical stability in acid aqueous solution up to pH 5. [10][11][12][13] Since it was first reported as a potential photoanode for photoelectrochemical cells (PEC) 27-32 and enhancing WO 3 stability in neutral solution using surface coating. 27 Recently, Yat Li's group reported that a hydrogen treatment at 350• C of hydrothermally synthesized WO 3 films enhanced photoactivity and photostability of the WO 3 electrode, due to the incorporation of W 5+ donors and oxygen vacancies. 24 The W 5+ states are believed to be more resistant to photocorrosion by peroxo-intermediates formed during water oxidation and they improve electron transport in the WO 3 films. Herein, we demonstrate that a similar performance increase can be achieved by in-situ electrochemical reduction of WO 3 particle films at +0.17 V vs. RHE (−0.04 V vs. NHE) in aqueous electrolyte. The reduction increases the water oxidation photocurrent of WO 3 by over an order of magnitude, up to 3.8 mA/cm 2 for an optimized device. This is comparable to the highest observed water oxidation photocurrents for WO 3 films reported in the literature (>2.5 mA cm −2 , AM 1.5, E App = 1.0 V vs. NHE). 18,23,[33][34][35][36] Furthermore, this photocurrent enhancement is achieved without the utilization of sophisticated film geometry design 18 or water oxidation electrocatalysts. [27][28][29][30][31] The relative photocurrent enhancement is most pronounced for films composed of bulk WO 3 particles (enhancement factor of 14 fold), followed by films of 50 nm particles (10 fold) and 30 nm particles (2 fold). The reduction treatment also improves the stability of WO 3 against photocorrosion; after reduction, 50% of the photocurrent persists after 1 hr operation, compared to 10% for an untreated film. The enhancement is preserved in air, when films are at roo...

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Section: Resultsmentioning

confidence: 99%

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Zhao

Olide

Osterloh

2014

J. Electrochem. Soc.

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“…WO 3 is a transition metal oxide made up of perovskite units, which is well‐known for its nonstoichiometric properties, as the lattice can withstand a considerable amount of oxygen deficiency 16. Only a partial loss of the WO 3 oxygen content is needed to affect its electronic band structure and increase its conductivity by a large amount 17.…”

Section: Fundamental Propertiesmentioning

confidence: 99%

“…Only a partial loss of the WO 3 oxygen content is needed to affect its electronic band structure and increase its conductivity by a large amount 17. However, the reduction of WO 3 is usually accompanied by structural changes 16. Some of the better known nonstoichiometric WO x compositions are W 20 O 58 , W 18 O 49 and W 24 O 68 .…”

Section: Fundamental Propertiesmentioning

confidence: 99%

Nanostructured Tungsten Oxide – Properties, Synthesis, and Applications

Zheng

Strano

et al. 2011

Adv Funct Materials

1,297

911

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This section focuses on the fundamental properties of nanostructured WO x and start with its various crystal structures and the conditions for phase transitions between these structures. The structures of nonstoichiometric WO x and WO 3 hydrates Nanostructured Tungsten Oxide -Properties, Synthesis, and Applications Metal oxides are the key ingredients for the development of many advanced functional materials and smart devices. Nanostructuring has emerged as one of the best tools to unlock their full potential. Tungsten oxides (WO x ) are unique materials that have been rigorously studied for their chromism, photocatalysis, and sensing capabilities. However, they exhibit further important properties and functionalities that have received relatively little attention in the past. This Feature Article presents a general review of nanostructured WO x , their properties, methods of synthesis, and a description of how they can be used in unique ways for different applications.

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“…Nano-WO 3 is readily reduced, and nonstoichiometry is reported to involve structural changes. [27][28][29] Substoichiometry gives rise to polarons, which change the optical properties and increase the absorption in the near-infrared (NIR) spectral region. 29,30 For small values of substoichiometry, x, crystals of WO 3Àx are reported to undergo a structural phase transition from the room temperature d phase to the low temperature e phase at T ; 250 K. 31 The d phase shows metallic behavior, and the e phase has insulating properties for the electron/hole carriers.…”

Section: Introductionmentioning

confidence: 99%

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

2012

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Nanostructured tungsten trioxide films were prepared by reactive dc magnetron sputtering at different working pressures P tot 5 1-4 Pa. The films were characterized by scanning electron microscopy, x-ray diffraction, Rutherford backscattering spectroscopy, Raman spectroscopy, and ultraviolet-visible spectrophotometry. The films were found to exhibit predominantly monoclinic structures and have similar band gap, E g % 2.8 eV, with a pronounced Urbach tail extending down to 2.5 eV. At low P tot , strained film structures formed, which were slightly reduced and showed polaron absorption in the near-infrared region. The photodegradation rate of stearic acid was found to correlate with the stoichiometry and polaron absorption. This is explained by a recombination mechanism, whereby photoexcited electron-hole pairs recombine with polaron states in the band gap. The quantum yield decreased by 50% for photon energies close to E g due to photoexcitations to band gap states lying below the O 2 affinity level.

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Magnetic susceptibility and thermoelectric power of tungsten intermediary oxides

Abstract: The magnetic susceptibility of the tungsten intermediary oxides WO3-x (0.05 Show more

Cited by 42 publications

References 33 publications

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Nanostructured Tungsten Oxide – Properties, Synthesis, and Applications

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

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Magnetic susceptibility and thermoelectric power of tungsten intermediary oxides

Abstract: The magnetic susceptibility of the tungsten intermediary oxides WO3-x (0.05 Show more

Cited by 42 publications

References 33 publications

Enhancing Majority Carrier Transport in WO3Water Oxidation Photoanode via Electrochemical Doping

Enhancing Majority Carrier Transport in WO3Water Oxidation Photoanode via Electrochemical Doping

Nanostructured Tungsten Oxide – Properties, Synthesis, and Applications

Structural and optical properties of visible active photocatalytic WO3 thin films prepared by reactive dc magnetron sputtering

Contact Info

Product

Resources

About

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering