Photoanodes Based on Nanostructured WO<sub>3</sub> for Water Splitting

Tacca, Alessandra; Meda, L.; Marra, Gianluigi; Savoini, Alberto; Caramori, Stefano; Cristino, Vito; Bignozzi, Carlo Alberto; Pedro, Victoria González; Boix, Pablo P.; Giménez, Sixto; Bisquert, Juan

doi:10.1002/cphc.201200069

Cited by 104 publications

(79 citation statements)

References 58 publications

(35 reference statements)

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“…3.5 μm. 33 This consists of a two-layers nanostructure: a compact oxide layer of ca. 1.3 μm originated by the first anodization of the starting tungsten foil, followed by a porous nanoparticle oxide layer of ca.…”

Section: 27mentioning

confidence: 99%

Photoelectrochemical water splitting using WO₃ photoanodes: the substrate and temperature roles

Dias

Lopes

Meda

et al. 2016

Phys. Chem. Chem. Phys.

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132

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The influence of the substrate on the performance of WO3 photoanodes is assessed as a function of the temperature. Two samples were studied: WO3 deposited on a FTO glass and anodized on a tungsten foil. Current-voltage curves and electrochemical impedance spectroscopy techniques were used to characterize these samples between 25 °C and 65 °C. The photocurrent-density increased with temperature for both samples and the onset potential shifted to lower potentials. However, for WO3/FTO, a negative shift of the dark current onset was also observed. The intrinsic resistivity of this substrate limits the photocurrent plateau potential range. On the other hand, this behavior was not observed for WO3/metal. Therefore, the earlier dark current onset observed for WO3/FTO was assigned to the FTO layer. The optimal operating temperatures observed were 45 °C and 55 °C for WO3/FTO and WO3/metal, respectively. For higher temperatures, the bulk electron-hole recombination phenomenon greatly affects the overall performance of WO3 photoanodes. The stability behavior was then studied at these temperatures over 72 h. For WO3/FTO, a crystalline-to-amorphous phase transformation occurred during the stability test, which may justify the current decrease observed after the aging period. The WO3/metal remained stable, maintaining its morphology and good crystallinity. Interestingly, the preferential orientation of the aged crystals was shifted to the (-222) and (222) planes, suggesting that this was responsible for its better and more stable performance. These findings provide crucial information for allowing further developments on the preparation of WO3 photoanodes, envisaging their commercial application in PEC water splitting cells.

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Section: 27mentioning

confidence: 99%

Photoelectrochemical water splitting using WO₃ photoanodes: the substrate and temperature roles

Dias

Lopes

Meda

et al. 2016

Phys. Chem. Chem. Phys.

Self Cite

132

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“…[27] The tungsten foil, prior to anodization, was carefully cleaned with acetone and ethanol and sonicated in an Alconox/water solution to remove surface contaminants and oily or greasy impurities.…”

Section: Wo3 Photoelectrode On Metal Substratementioning

confidence: 99%

“…It can be observed that the anodized metal sample has a significantly higher photocurrent density than the sample deposited onto a TCO glass substrate; at 1.45 VRHE the metallic sample (coded hereafter as WO3-Metal) produces 0.9 mA·cm -2 and the glass sample (coded hereafter as WO3-Glass) produces 0.15 mA·cm -2 ; actually, this behavior is in line with the efficiency values reported in literature. [27,28] The differences observed in the photocurrents are not only due to the preparation method but also due to the higher charge transport resistance through the transparent conductive oxide (TCO) layer in the glass substrate. The EIS spectra will allow to discriminate the series resistances in glass and metal substrates, which are directly related to the charge transport resistance on them -cf.…”

Section: Wo3 Photoelectrodesmentioning

confidence: 99%

An innovative photoelectrochemical lab device for solar water splitting

Lopes

Dias

Andrade

et al. 2014

Solar Energy Materials and Solar Cells

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A photoelectrochemical (PEC) device capable of splitting water into storable hydrogen fuel by the direct use of solar energy is becoming a very attractive technology since it is clean and sustainable. Indeed, real field experiments are being developed in order to assess technological issues for large-scale usage under outdoor conditions. Following the need for developing photoelectrochemical devices with an optimized design that allows reaching a commercial performance level, the present works describes an innovative PEC cell for testing different photoelectrodes configurations, suitable for continuous operation and for easily collect the evolved gases. Moreover, a porous Teflon ® diaphragm useable for a wide range of aqueous electrolyte solutions is tested. Two semiconductors were investigated: tungsten trioxide and undoped hematite. The WO3 photoelectrodes were deposited in two different substrates: i) anodized WO3 photoelectrodes on a metal substrate and ii) WO3 deposited by blade spreading method on a TCO glass substrate.The undoped-Fe2O3 photoanode was deposited by ultrasonic spray pyrolysis technique in a TCO glass substrate. The material deposited on glass substrates allows to obtain transparent photoelectrodes. Photocurrent-voltage characteristics were obtained for all samples characterized under three different conditions: i) no membrane separating the anode and the cathode evolution; ii) using a Teflon ® diaphragm and iii) using a Nafion ® 212 membrane. The transparent samples (photoanodes deposited on glass substrates) produced the highest values of photocurrent when the Teflon ® diaphragm was used. This

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“…[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…”

mentioning

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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Photoanodes Based on Nanostructured WO₃ for Water Splitting

Cited by 104 publications

References 58 publications

Photoelectrochemical water splitting using WO₃ photoanodes: the substrate and temperature roles

Photoelectrochemical water splitting using WO₃ photoanodes: the substrate and temperature roles

An innovative photoelectrochemical lab device for solar water splitting

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

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Photoanodes Based on Nanostructured WO3 for Water Splitting

Cited by 104 publications

References 58 publications

Photoelectrochemical water splitting using WO3 photoanodes: the substrate and temperature roles

Photoelectrochemical water splitting using WO3 photoanodes: the substrate and temperature roles

An innovative photoelectrochemical lab device for solar water splitting

Enhancing Majority Carrier Transport in WO3Water Oxidation Photoanode via Electrochemical Doping

Contact Info

Product

Resources

About

Photoanodes Based on Nanostructured WO₃ for Water Splitting

Photoelectrochemical water splitting using WO₃ photoanodes: the substrate and temperature roles

Photoelectrochemical water splitting using WO₃ photoanodes: the substrate and temperature roles

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping