Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and Oxygen

Bard, Allen J.; Fox, Marye Anne

doi:10.1021/ar00051a007

Cited by 2,511 publications

(1,795 citation statements)

References 24 publications

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“…[56] To close the photocatalytic cycle, H 2 production has to occur either through reduction and protonation of the HFe II Fe I intermediate, which is more easily reduced than the starting Fe I Fe I complex, [56] or through bimolecular combination of two iron hydride molecules. Although the bimolecular pathway cannot be excluded, we favor the mechanism involving the reduction and protonation of the iron hydride intermediate because the initial rate of H 2 production is not very sensitive to the concentration of catalyst for [1] 0.1 mm (Figure 2). …”

Section: Resultsmentioning

confidence: 99%

Photocatalytic Hydrogen Production Using Models of the Iron–Iron Hydrogenase Active Site Dispersed in Micellar Solution

2013

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International audienceIron–thiolate complexes of the type [Fe2(μ-bdt)(CO)6−xP(OMe3)x] (bdt=S2C6H4=benzenedithiolate, x≤2) are simplified models of iron–iron hydrogenase enzymes. Recently, we have shown that these water-insoluble organometallic complexes, when included into micelles formed by sodium dodecyl sulfate (SDS), are good catalysts for the electrochemical production of hydrogen in aqueous solutions at pH<6. We herein report that the all-CO derivative [Fe2(μ-bdt)(CO)6] (1), owing to its comparatively low reduction potential, is also a robust molecular catalyst for visible-light-driven production of H2 in aqueous SDS solutions at pH 10.5. Irradiation at λ=455 nm of a system consisting of complex 1, Eosin Y as a sensitizer, and triethylamine as an electron donor produced up to 0.86 mL of H2 in 4.5 h, corresponding to a turnover number of 117 mol of H2 per mol of catalyst. In the presence of a large excess of sensitizer, the production of H2 lasted for more than 30 h, stressing the relative stability of complex 1 under the photocatalytic conditions used herein. Thermodynamic considerations and UV/Vis spectroscopy experiments suggest that the catalytic cycle begins with the photo-driven reduction of complex 1. The reduced intermediate reacts with a proton source to yield iron hydride. Subsequent reduction and protonation steps produce H2, regenerating the starting complex. As a result, the iron–thiolate complex 1 is a versatile proton reduction catalyst that can utilize either solar or electrical energy inputs, providing a starting point for the construction of noble metal-free molecular systems for renewable H2 production

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Section: Resultsmentioning

confidence: 99%

Photocatalytic Hydrogen Production Using Models of the Iron–Iron Hydrogenase Active Site Dispersed in Micellar Solution

2013

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“…13 However, there are relatively few candidate materials for an acid-stable photoanode with an appropriate band gap. 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.…”

Section: Introductionmentioning

confidence: 99%

“…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%

“…[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. 14 The photogenerated minority-carrier holes in the valence band of WO 3 have a potential of B2.97 V vs. NHE at pH 0. 33 This potential is sufficient to drive many competing reactions, thus limiting the faradaic oxygen evolution efficiency on bare WO 3 .…”

Section: Introductionmentioning

confidence: 99%

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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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“…1) [9,[27][28][29][30][31]. In type 1 PCs, light absorption and charge separation occur at a single absorber particle connected to one or several co-catalysts to complete the circuit for water electrolysis.…”

Section: Photoelectrochemical Water Splitting As a Pathway To Sustainmentioning

confidence: 99%

Nanoscale Effects in Water Splitting Photocatalysis

Osterloh

2015

Topics in Current Chemistry

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From a conceptual standpoint, the water photoelectrolysis reaction is the simplest way to convert solar energy into fuel. It is widely believed that nanostructured photocatalysts can improve the efficiency of the process and lower the costs. Indeed, nanostructured light absorbers have several advantages over traditional materials. This includes shorter charge transport pathways and larger redox active surface areas. It is also possible to adjust the energetics of small particles via the quantum size effect or with adsorbed ions. At the same time, nanostructured absorbers have significant disadvantages over conventional ones. The larger surface area promotes defect recombination and reduces the photovoltage that can be drawn from the absorber. The smaller size of the particles also makes electron-hole separation more difficult to achieve. This chapter discusses these issues using selected examples from the literature and from the laboratory of the author.

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Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and Oxygen

Cited by 2,511 publications

References 24 publications

Photocatalytic Hydrogen Production Using Models of the Iron–Iron Hydrogenase Active Site Dispersed in Micellar Solution

Photocatalytic Hydrogen Production Using Models of the Iron–Iron Hydrogenase Active Site Dispersed in Micellar Solution

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

Nanoscale Effects in Water Splitting Photocatalysis

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