The Nature of Oxide Films on Tungsten in Acidic and Alkaline Solutions

Lillard, R. S.; Kanner, G.S.; Butt, Darryl P.

doi:10.1149/1.1838704

Cited by 114 publications

(99 citation statements)

References 7 publications

(4 reference statements)

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“…A key drawback of WO 3 is its chemical instability at pH > 4. [ 19 ] However, spin-coating of TiNi SSP (4 × 60 µL cm −2 , 5 × 10 −3 M in dry toluene) on nanoWO 3 forms nanoWO 3 |TiNi pre with a uniform Tiand Ni-containing fi lm exhibiting a nanostructured morphology (Figure 5 c), which allows it to be employed in neutral-alkaline solution. The sheet thickness was increased from ≈30 to 300 nm after depositing the Ti-and Ni-containing fi lm.…”

Section: Ssp-coated Photoelectrodes and Performancementioning

confidence: 99%

Multifunctional Coatings from Scalable Single Source Precursor Chemistry in Tandem Photoelectrochemical Water Splitting

Lai

Palm

Reisner

2015

Advanced Energy Materials

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The straightforward and inexpensive fabrication of stabilized and activated photoelectrodes for application to tandem photoelectrochemical (PEC) water splitting is reported. Semiconductors such as Si, WO3, and BiVO4 can be coated with a composite layer formed upon hydrolytic decomposition of heterobimetallic single source precursors (SSPs) based on Ti and Ni, or Ti and Co in a simple single‐step process under ambient conditions. The resulting 3d‐transition metal oxide composite films are multifunctional, as they protect the semiconductor electrode from corrosion with an amorphous TiO2 coating and act as bifunctional electrocatalysts for H2 and O2 evolution based on catalytic Ni or Co species. Thus, this approach enables the use of the same precursors for both photoelectrodes in tandem PEC water splitting, and SSP chemistry is thereby established as a highly versatile low‐cost approach to protect and activate photoelectrodes. In an optimized system, SSP coating of a Si photocathode and a BiVO4 photoanode resulted in a benchmark noble metal‐free dual‐photoelectrode tandem PEC cell for overall solar water splitting with an applied bias solar‐to‐hydrogen conversion efficiency of 0.59% and a half‐life photostability of 5 h.

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Section: Ssp-coated Photoelectrodes and Performancementioning

confidence: 99%

Multifunctional Coatings from Scalable Single Source Precursor Chemistry in Tandem Photoelectrochemical Water Splitting

Lai

Palm

Reisner

2015

Advanced Energy Materials

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“…At higher pH, OH À ions induce chemical dissolution by the reaction WO 3 (s) + OH À -WO 4 2À + H + . 30,31 Even in acidic conditions, some photocorrosion of WO 3 has been observed due to the formation of peroxo-species as intermediates during water oxidation. [22][23][24]32 Although peroxide formation and the oxidation of most acid counterion species are reactions that are thermodynamically less feasible than water oxidation, the kinetics of these reactions are often more favorable than oxygen evolution.…”

Section: Introductionmentioning

confidence: 99%

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

Spurgeon

Velázquez

McDowell

2014

Phys. Chem. Chem. Phys.

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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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“…Except for the case of OH À , which plays an important role in the dissolution of WO 3 [31], other anions (PO 3À 4 , SO 2À 4 , or Cl À ) do not alter the dissolution rate law, which remains independent of layer thickness throughout the entire dissolution process. This is in agreement with our observation that in neutral to basic media the WO 3 layer was more easily removed from its Pt substrate than it was in concentrated acid solutions.…”

Section: Wo 3 Electrodepositionmentioning

confidence: 98%

Electroanalysis of Bromate, Iodate and Chlorate at Tungsten Oxide Modified Platinum Microelectrode Arrays

Ordeig¹,

Banks²,

Campo³

et al. 2006

Electroanalysis

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This article describes the direct detection of Bromate, but also of chlorate and iodate, using modified arrays of platinum ultramicroelectrodes. The detection limits for these ions are IOThe formation of a suitable tungsten oxide layer and the optimum analytical conditions are described. These oxide layers are formed electrochemically from hydrogen peroxide-tungstanate solutions in acid conditions. Although film stability may be an issue, particularly at pH > 3, these modified arrays of microelectrodes can be used for analytical purposes. After the analysis, the modifying oxide is easily removed and the Pt microelectrode array recovers its original properties. Finally, the detection limit is calculated using a propagation of errors approach which in the present context turned out more appropriate than IUPACs 3s.

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The Nature of Oxide Films on Tungsten in Acidic and Alkaline Solutions

Cited by 114 publications

References 7 publications

Multifunctional Coatings from Scalable Single Source Precursor Chemistry in Tandem Photoelectrochemical Water Splitting

Multifunctional Coatings from Scalable Single Source Precursor Chemistry in Tandem Photoelectrochemical Water Splitting

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

Electroanalysis of Bromate, Iodate and Chlorate at Tungsten Oxide Modified Platinum Microelectrode Arrays

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