Size effects of WO3 nanocrystals for photooxidation of water in particulate suspension and photoelectrochemical film systems

Hong, Suk Joon; Jun, Hwichan; Borse, Pramod H.; Lee, Jae Sung

doi:10.1016/j.ijhydene.2009.02.006

Cited by 224 publications

(144 citation statements)

References 32 publications

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“…51 With the carrier concentrations determined from MottSchottky plots in Figure 5A and a flatband potential of +0.55 V for WO 3 , space charge widths of 18 nm and 0.5 nm are calculated for WO 3 nanoplates before and after reduction, respectively, at an applied potential of +0.8 V. 51 Front versus back illumination experiments can be useful to evaluate the resistance losses in nanostructured photoelectrodes. 40,52 Figure 6A shows the photocurrent responses of an as-prepared WO 3 film. Back illumination provides a higher photocurrent than front illumination, suggesting that photocurrent from front illumination is limited by electron transport through WO 3 film and collection at the back substrate.…”

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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“…[15][16][17][18] 28-34 Although a sol-gel technique is one of the simplest and lowest-cost procedures selected for a wide range of applications, there have been only a few reports on photoelectrochemical characteristics of the WO 3 film prepared by a sol-gel technique. [5][6][7][8] Several techniques for improving photoresponse of thin film electrodes W/WO 3 have already been proposed.…”

Section: Introductionmentioning

confidence: 99%

“…[11][12][13][14] Tungsten trioxide has been an excellent alternative material, since it presents smaller band gap energy (2.4-2.8 eV) and can be photoexcited in the visible region close to the UV region. [15][16][17][18] However, most of the studies found in literature explore tungsten trioxide only as electrochromic applications and solar energy conversion.…”

Section: Introductionmentioning

confidence: 99%

Nanoporous of W/WO3 Thin Film Electrode Grown by Electrochemical Anodization Applied in the Photoelectrocatalytic Oxidation of the Basic Red 51 used in Hair Dye

Zanoni¹

2011

J. Braz. Chem. Soc.

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Eletrodo nanoporoso auto-organizado de W/WO 3 pode ser obtido através da anodização eletroquímica de placas de W em solução de NaF 0,15 mol L -1 como eletrólito suporte, aplicando uma rampa de potencial de 0,2 V s -1 , até alcançar 60 V, mantendo por 2 h. A forma monoclínica altamente ordenada do WO 3 é majoritária quando calcinado a 450 0 C durante 30 min, obtendo uma maior fotoatividade quando irradiada na luz visível em relação a luz UV. O eletrodo promove a descoloração total do vermelho básico 51, utilizado em tinturas de cabelo, após 60 min de oxidação fotoeletrocatalítica, em densidade de corrente de 1,25 mA cm -2 e irradiação em comprimento de onda 420-630 nm. Nessa condição foi obtido 63% de mineralização. Uma menor eficiência é obtida para o sistema irradiado por comprimento de onda (280-400 nm), quando apenas 40% de remoção de carbono orgânico total é obtida, necessitando de 120 min de tratamento para a descoloração total da solução do vermelho básico 51.Self-organized W/WO 3 nanoporous electrodes can be obtained by simple electrochemical anodization of W foil in 0.15 mol L -1 NaF solution as the supporting electrolyte, applying a ramp potential of 0.2 V s -1 until it reached 60 V, which was maintained for 2 h. The monoclinic form is majority in the highly ordered WO 3 annealed at 450 °C , obtaining a higher photoactivity when irradiated by visible light than by UV light. The electrode promotes complete discoloration of the investigated basic red 51 dye after 60 min of photoelectrocatalytic oxidation, on current density of 1.25 mA cm -2 and irradiation on wavelength of 420-630 nm. In this condition it was obtained 63% of mineralization. Lower efficiency is obtained for the system irradiated by wavelength (280-400 nm) when only 40% of total organic carbon removal is obtained and 120 min is required for complete discoloration.Keywords: W/WO 3 electrodes, electrochemical anodization, photoelectrocatalysis, basic red 51, hair dye IntroductionThe use of TiO 2 as photoanode in photoelectrocatalytic degradation of pollutants is well known in literature. [1][2][3][4][5][6][7][8][9][10] Nevertheless, this material presents band gap energy around 3.2 eV, which is photoexcited only in the ultraviolet region (l ≤ 380 nm).11-14 Tungsten trioxide has been an excellent alternative material, since it presents smaller band gap energy (2.4-2.8 eV) and can be photoexcited in the visible region close to the UV region. [15][16][17][18] 28-34 Although a sol-gel technique is one of the simplest and lowest-cost procedures selected for a wide range of applications, there have been only a few reports on photoelectrochemical characteristics of the WO 3 film prepared by a sol-gel technique. [5][6][7][8] Several techniques for improving photoresponse of thin film electrodes W/WO 3 have already been proposed. The electrodeposited Pt/WO 3 catalysts have improved the oxidation of methanol and formic acid. [35][36][37][38] The WO x films with Pt, Sn, and Ru dopands were used for electrooxidation of acetaldehyde. Some authors have de...

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“…The narrow band gap of 2.20 -2.80 eV helps in absorption of ultraviolet region and blue region of visible light in solar spectrum [22][23][24][25]. Furthermore, WO 3 has been investigated with the aim of improving catalyst activity and stability in the irradiated aqueous environment [26][27][28][29]. Tungsten trioxide powders prepared from various W precursors has been studied by Bamwenda and Arakawa [30].…”

Section: Ng Et Al: Fabrication and Characterization Of Fe-doped Tungsmentioning

confidence: 99%

FABRICATION AND CHARACTERIZATION OF Fe-DOPED TUNGSTEN TRIOXIDE PHOTOELECTRODES IN AQUEOUS MEDIUM USING TUNGSTIC ACID AND FERROCENE AS STARTING MATERIALS

Hang

Jaafar

Minggu³

et al. 2016

MJAS

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Different compositions of Fe-doped tungsten trioxide thin films were synthesized on fluorine-doped tin oxide (FTO) glass substrate by sol-gel method, with ferrocene and tungstic acid as starting materials. The synthesized thin films was characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), UV/Vis spectrophotometer and photoelectrochemical (PEC) analysis. The results show that the surface morphology of the thin films became rough and the grain size increased along with the concentration of Fe. Monoclinic structure of tungsten trioxide was obtained for all doped and undoped WO 3 and red-shift can be observed from UV-vis spectrum. Band gap reduced from 2.74 eV of undoped WO 3 thin films to 2.60 eV of 20 % Fe-doped WO 3 thin films. Photoactivities of all Fe-doped WO 3 are higher than undoped thin films. The highest photoactivities contributed by 5 % Fe-doped WO 3 films with photocurrent densities measured was 0.148 mA/cm 2 , which is 3 times higher compared to undoped WO 3 .Keywords: Fe-doped WO 3 , direct water splitting, photoelectrochemical cell, photoanode Abstrak Filem nipis tungsten trioksida terdop Fe berbagai komposisi telah disediakan di atas kaca substrat FTO (fluorine-doped tin oxide) dengan kaedah sol-gel, dengan menggunakan ferosin dan asid tingstik sebagai bahan pemula. Filem nipis yang terhasil kemudiannya dicirikan dengan pembelauan sinar X (XRD), mikroskopi elektron pengimbasan (SEM), UV/Vis spektrofotometer dan analisis fotoelektrokimia. Keputusan menunjukkan bahawa morfologi permukaan filem nipis menjadi kasar dan saiz butiran bertambah dengan penambahan kepekatan Fe. Tungsten trioksida yang berstruktur monoklinik telah dihasilkan dan anjakan merah telah diperhatikan di dalam spectrum UV-vis. Jurang tenaga telah berkurang dari 2.74 eV (WO 3 tulen) kepada 2.60 eV (20 % Fe-dop WO 3 ). Fotoaktiviti WO 3 terdop Fe adalah lebih tinggi berbanding WO 3 tulen. Fotoaktiviti yang tertinggi dicatatkan oleh filem 5 % WO 3 terdop Fe dengan ketumpatan fotoarus 0.148 mA/cm 2 . Ia adalah 3 kali ganda lebih tinggi berbanding WO 3 tulen.Kata kunci: Fe-dop WO 3 , pembelahan air secara langsung, sel fotoelektrokimia, fotoanod

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Size effects of WO3 nanocrystals for photooxidation of water in particulate suspension and photoelectrochemical film systems

Cited by 224 publications

References 32 publications

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Nanoporous of W/WO3 Thin Film Electrode Grown by Electrochemical Anodization Applied in the Photoelectrocatalytic Oxidation of the Basic Red 51 used in Hair Dye

FABRICATION AND CHARACTERIZATION OF Fe-DOPED TUNGSTEN TRIOXIDE PHOTOELECTRODES IN AQUEOUS MEDIUM USING TUNGSTIC ACID AND FERROCENE AS STARTING MATERIALS

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Size effects of WO3 nanocrystals for photooxidation of water in particulate suspension and photoelectrochemical film systems

Cited by 224 publications

References 32 publications

Enhancing Majority Carrier Transport in WO3Water Oxidation Photoanode via Electrochemical Doping

Enhancing Majority Carrier Transport in WO3Water Oxidation Photoanode via Electrochemical Doping

Nanoporous of W/WO3 Thin Film Electrode Grown by Electrochemical Anodization Applied in the Photoelectrocatalytic Oxidation of the Basic Red 51 used in Hair Dye

FABRICATION AND CHARACTERIZATION OF Fe-DOPED TUNGSTEN TRIOXIDE PHOTOELECTRODES IN AQUEOUS MEDIUM USING TUNGSTIC ACID AND FERROCENE AS STARTING MATERIALS

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Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping