A highly stable, efficient visible-light driven water photoelectrolysis system using a nanocrystalline WO3 photoanode and a methane sulfonic acid electrolyte

Solarska, Renata; Jurczakowski, Rafał; Augustyński, Jan

doi:10.1039/c2nr11573e

Cited by 105 publications

(115 citation statements)

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“…Electrochemical impedance spectroscopy (EIS) is a powerful technique to characterize charge transfer processes in nanostructured WO 3 films. 49,50 Before reduction, two semi-circles are observed in the Nyquist plot ( Figure 5B), indicating two limiting charge transfer processes with distinct time constants (radii) in the as-prepared WO 3 nanoplate film. The first arc with the smaller radius is assigned to electron transport through the film, whereas the second arc with the larger radius is related to the interfacial charge transfer at the WO 3 -electrolyte interface.…”

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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“…Tungsten trioxide, WO 3 , an earth-abundant, oxidatively stable semiconductor, is one such material that could fulfill the role of photoanode. [14][15][16][17][18][19][20][21][22][23][24] In most deposition methods, the presence of oxygen vacancies serve as shallow electron donors and naturally dope the WO 3 n-type. 25 Its band gap of 2.6 eV is higher than ideal for the large band gap absorber in a tandem cell.…”

Section: Introductionmentioning

confidence: 99%

Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

Spurgeon

Velázquez

McDowell

2014

Phys. Chem. Chem. Phys.

101

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WO 3 is a promising candidate for a photoanode material in an acidic electrolyte, in which it is more stable than most metal oxides, but kinetic limitations combined with the large driving force available in the WO 3 valence band for water oxidation make competing reactions such as the oxidation of the acid counterion a more favorable reaction. The incorporation of an oxygen evolving catalyst (OEC) on the WO 3 surface can improve the kinetics for water oxidation and increase the branching ratio for O 2 production. Ir-based OECs were attached to WO 3 photoanodes by a variety of methods including sintering from metal salts, sputtering, drop-casting of particles, and electrodeposition to analyze how attachment strategies can affect photoelectrochemical oxygen production at WO 3 photoanodes in 1 M H 2 SO 4 . High surface coverage of catalyst on the semiconductor was necessary to ensure that most minority-carrier holes contributed to water oxidation through an active catalyst site rather than a sidereaction through the WO 3 /electrolyte interface. Sputtering of IrO 2 layers on WO 3 did not detrimentally affect the energy-conversion behavior of the photoanode and improved the O 2 yield at 1.2 V vs. RHE from B0% for bare WO 3 to 50-70% for a thin, optically transparent catalyst layer to nearly 100% for thick, opaque catalyst layers. Measurements with a fast one-electron redox couple indicated ohmic behavior at the IrO 2 /WO 3 junction, which provided a shunt pathway for electrocatalytic IrO 2 behavior with the WO 3 photoanode under reverse bias. Although other OECs were tested, only IrO 2 displayed extended stability under the anodic operating conditions in acid as determined by XPS.

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“…[31] Recently, we showed that, in contrast with most of acidic electrolytes (HClO 4 , H 2 SO 4 others), the methane-sulfonic acid supporting electrolyte does not undergo changes over the photoelectrolysis and insures stable long-term operation of a WO 3 photoanode. [34] In fact, Raman spectroscopic analyses of a 1 m CH 3 SO 3 H solution that had been used as water splitting electrolyte, with the WO 3 photo anode irradiated with high intensity light over 70 h, did not show any spectral changes. This makes an essential difference with respect to, e.g., the H 2 SO 4 electrolyte that under similar conditions underwent to a large extent a conversion into persulfuric acid.…”

mentioning

confidence: 98%

Highly Efficient and Stable Solar Water Splitting at (Na)WO₃ Photoanodes in Acidic Electrolyte Assisted by Non‐Noble Metal Oxygen Evolution Catalyst

Sarnowska

Bieńkowski

Barczuk

et al. 2016

Advanced Energy Materials

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≈0.8 V versus RHE, for the α-Fe 2 O 3 .[9] Consequently, to operate as water splitting photoanodes, both WO 3 and α-Fe 2 O 3 require application of an external bias.These early observations have led to the concept of a tandem water splitting system. [12,13] One of the proposed configurations combined a photoelectrolysis cell, featuring a WO 3 photoanode and a metallic cathode, with a dye-sensitized solar cell (DSSC). [14] This concept has been recently demonstrated in dual absorber tandem cell in which the WO 3 photoanode was associated with a single-junction DSSC placed behind the photoelectroanalyzer. [15] In such a configuration, the semitransparent WO 3 film, supported on a conductive glass substrate, absorbs the blue wavelengths of solar beam and transmits its yellow and red parts that are captured by the DSS photovoltaic cell that acts as a photodriven bias. The solar-to-hydrogen (STH) efficiency measured over steady-state operation of the device was 3.1%, corresponding to 2.52 mA cm −2 water oxidation photocurrent density reached at a WO 3 photoanode under ≈1 V bias. Due to its onset potential, much more positive than that of WO 3 , two times lower photocurrent was recorded under such conditions for an α-Fe 2 O 3 photoanode. [15] Given that at 0.9-1 V the DSSC can deliver currents exceeding 5 mA cm −2 , it is clearly the photo anode that is the bottleneck of the tandem device.Attempts to improve the water splitting performance of the semiconductor photoanodes involve the use of OER catalysts. In contrast with the "dark" electrolysis of water where sluggish kinetics of oxygen evolution manifests itself in significant overvoltages, in the PEC oxidation of water at n-type semiconducting photoanodes it results in charge recombination losses, becoming apparent through a positive shift of the photo current onset potential and a slow subsequent rise of the photo current. In fact, although the potential at which positive holes are photogenerated in metal oxide semiconductors (TiO 2 , WO 3 , BiVO 4, Fe 2 O 3 ) is by far sufficiently positive to afford the OER, the slow charge transfer to the solution species (i.e., OH − ions or H 2 O molecules) leads to enhanced electron-hole (e − -h + ) recombination.Common approach to reduce recombination losses involves deposition of electrocatalysts on the photoelectrode surface. Either metals or metal compounds such as mixed cobalt phosphate-oxide (Co-Pi) [16][17][18] or, more recently, oxyhydroxides of nickel and iron [19,8] were coated on the surface of α-Fe 2 O 3 or of another metal oxide photoanode BiVO 4 . Notwithstanding its high activity for the OER, the application of the Co-Pi in PEC devices is however restricted by its filtering of the incident light. [20] The Co-Pi and Ni 1−x Fe x OOH deposits are stable in Electrolysis of water is an attractive approach to produce hydrogen fuel, however the conventional process is energetically expensive requiring ≈1.7-1.8 V that includes 0.5-0.6 V overvoltage losses due principally to oxygen-evolution half-reaction. [1,2] Water s...

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A highly stable, efficient visible-light driven water photoelectrolysis system using a nanocrystalline WO3 photoanode and a methane sulfonic acid electrolyte

Cited by 105 publications

References 12 publications

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Enhancing Majority Carrier Transport in WO₃Water Oxidation Photoanode via Electrochemical Doping

Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

Highly Efficient and Stable Solar Water Splitting at (Na)WO₃ Photoanodes in Acidic Electrolyte Assisted by Non‐Noble Metal Oxygen Evolution Catalyst

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A highly stable, efficient visible-light driven water photoelectrolysis system using a nanocrystalline WO3 photoanode and a methane sulfonic acid electrolyte

Cited by 105 publications

References 12 publications

Enhancing Majority Carrier Transport in WO3Water Oxidation Photoanode via Electrochemical Doping

Enhancing Majority Carrier Transport in WO3Water Oxidation Photoanode via Electrochemical Doping

Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

Highly Efficient and Stable Solar Water Splitting at (Na)WO3 Photoanodes in Acidic Electrolyte Assisted by Non‐Noble Metal Oxygen Evolution Catalyst

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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

Highly Efficient and Stable Solar Water Splitting at (Na)WO₃ Photoanodes in Acidic Electrolyte Assisted by Non‐Noble Metal Oxygen Evolution Catalyst