Photocatalytic decomposition of water into H2 and O2 by a two-step photoexcitation reaction using a WO3 suspension catalyst and an Fe3+/Fe2+ redox system

Sayama, Kazuhiro; Yoshida, Rika; Kusama, Hitoshi; Okabe, Kiyomi; Abe, Yoshimoto; Arakawa, Hironori

doi:10.1016/s0009-2614(97)00903-2

Cited by 186 publications

(123 citation statements)

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“…The depositiondehydration cycle was then repeated. Aer 5-6 cycles, the electrode was annealed at 500 C in air for 1 h, yielding a pale yellow lm of WO 3 . The mass and thickness of the electrodeposited WO 3 lm were determined using a Sartorius CPA225D semi-micro balance and a Dektak XT prolometer, respectively.…”

Section: à2mentioning

confidence: 99%

“…Several studies [11][12][13][14] of the photoelectrochemical behavior of WO 3 in aqueous electrolytes have recently suggested that an alternative process, in which oxidation of electrolyte anions, such as Cl À , HSO 4 À , and ClO 4 À , effectively competes with oxidation of water at the WO 3 /electrolyte interface, dominates the photoanodic behavior of n-type WO 3 especially under acidic conditions. Although some of the oxidation products (Cl 2 and S 2 O 8 2À ) have been conrmed experimentally, 11-13 the importance of the oxidation of water to produce OH_ as an energetic intermediate, relative to the oxidation of electrolyte anions, has yet to be fully elucidated.…”

Section: Introductionmentioning

confidence: 99%

“…The at-band potential (E  ) of n-type WO 3 , at $0.4 V vs. NHE, 19,20 is too positive to effect the reduction of protons with no external bias applied to the system. Given the standard electrode potential for water oxidation, E 0 ¼ 1.23 V vs. NHE, WO 3 photoanodes can therefore in theory generate an open-circuit voltage (V oc ) of at most $0.8 V for water oxidation.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, much of the band gap energy of WO 3 (E g ¼ 2.6 eV) 21 is not used electrochemically, and a substantial bias voltage from the photocathode is required to achieve overall water splitting. In nonaqueous electrolytes, existing knowledge about Si photoelectrodes 22,23 predicts that both the E  of WO 3 and the Nernstian potential of the solution are tunable beyond these limits. To maximize the V oc of regenerative photoelectrochemical cells, a nonaqueous redox system with a very positive Nernstian potential (e.g., >1.5 V vs. NHE) therefore needs to be identied.…”

Section: Introductionmentioning

confidence: 99%

“…We describe herein the nonaqueous photoelectrochemistry of WO 3 , and report the voltammetric, spectral response, and electrochemical impedance data obtained by using a combination of four anions (Cl À , CH 3 was prepared in two steps 25,26 using decaborane (Alfa Aesar 87892, 98%), bromine, and tetra(n-butyl)ammonium bromide, and was subsequently recrystallized from acetone/ethanol as colorless needles. TBA 2 B 10 Br 10 is not hygroscopic and is readily soluble in aprotic organic solvents.…”

Section: Introductionmentioning

confidence: 99%

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Photoelectrochemical oxidation of anions by WO3 in aqueous and nonaqueous electrolytes

Coridan

Brunschwig

et al. 2013

Energy Environ. Sci.

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The behavior of WO 3 photoanodes has been investigated in contact with a combination of four anions (Cl ) and three solvents (water, acetonitrile, and propylene carbonate), to elucidate the role of the semiconductor surface, the electrolyte, and redox kinetics on the current density vs. potential properties of n-type WO 3 . In 1.0 M aqueous strong acids, although the flat-band potential (E fb ) of WO 3 was dominated by electrochemical intercalation of protons into WO 3 , the nature of the electrolyte influenced the onset potential (E on ) of the anodic photocurrent. In aprotic solvents, the electrolyte anion shifted both E fb and E on , but did not significantly alter the overall profile of the voltammetric data. For 0.50 M tetra(n-butyl)ammonium perchlorate in propylene carbonate, the internal quantum yield exceeded unity at excitation wavelengths of 300-390 nm, indicative of current doubling. Broader contextElectrolytes are an indispensable constituent in (photo)electrochemistry for forming interfacial double layers and conducting currents. Nonetheless, it is generally considered that the role of electrolytes in (photo)electrochemistry is merely supporting and implicit, because the identity and concentration of electrolytes do not directly determine the electrode potentials and current densities. Results from this work suggest that when in contact with various aqueous and nonaqueous solutions and under simulated solar illumination, thin-lm WO 3 photoanodes oxidized primarily the electrolyte anions in spite of the dominant molarity of the solvent in the electrolyte solutions. The priority of anion oxidation has been utilized to construct nonaqueous, regenerative photoelectrochemical cells that produce large open-circuit voltages. In addition to O 2 (g) evolution from water, such electrolyte effects can result in undesired side reactions, and such processes should be taken into account when WO 3 photoanodes are incorporated into multi-component devices for solar-driven water splitting.

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Section: à2mentioning

confidence: 99%