Robust dye-sensitized overall water splitting system with two-step photoexcitation of coumarin dyes and metal oxide semiconductors

Abe, Ryu; Shinmei, Kenichi; Hara, Kohjiro; Ohtani, Bunsho

doi:10.1039/b905935k

Cited by 157 publications

(117 citation statements)

References 19 publications

(7 reference statements)

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“…However, the doping polarity of the two light-absorbing components can be interchanged, with the top junction being the photocathode and the bottom being the photoanode. Photochemical diodes, 22 dye-sensitized photosystems, 3,8,9 and two-component particulate systems with redox relays (equivalent to an Ohmic contact in terms of a circuit element) 6,7 can be categorized as the photoanode + photocathode PEC system. With minimization of both gas crossover and back reactions, the STH efficiency limit of two-component particulate systems will be comparable to that of photochemical diodes.…”

Section: Theorymentioning

confidence: 99%

“…Similarly, bi-component particulate or particle-molecular dye photosystems have been suggested for use in spontaneous water splitting under visible-light illumination using a suitable redox mediator. [6][7][8][9] However, a membrane that is selective to the redox mediator is necessary, because the evolved H 2 and O 2 should be separated by the membrane for safety considerations. Additionally, undesirable back-reactions, e.g.…”

Section: Introductionmentioning

confidence: 99%

“…10 By using light-absorbing materials (either inorganic semiconductors or organic dye-molecules) with complementary absorption spectra, a two-component photosystem 8,9 or a two-junction PEC system can effectively capture various portions of the solar spectrum, providing the photovoltage needed to split water. However, the STH efficiency depends on both the photovoltage and the photocurrent density of the light absorber, and the maximum photocurrent density decreases with an increasing number of junctions.…”

Section: Introductionmentioning

confidence: 99%

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An analysis of the optimal band gaps of light absorbers in integrated tandem photoelectrochemical water-splitting systems

Xiang

Haussener

et al. 2013

Energy Environ. Sci.

530

545

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The solar-to-hydrogen (STH) efficiency limits, along with the maximum efficiency values and the corresponding optimal band gap combinations, have been evaluated for various combinations of light absorbers arranged in a tandem configuration in realistic, operational water-splitting prototypes. To perform the evaluation, a current-voltage model was employed, with the light absorbers, electrocatalysts, solution electrolyte, and membranes coupled in series, and with the directions of optical absorption, carrier transport, electron transfer and ionic transport in parallel. The current density vs. voltage characteristics of the light absorbers were determined by detailed-balance calculations that accounted for the ShockleyQueisser limit on the photovoltage of each absorber. The maximum STH efficiency for an integrated photoelectrochemical system was found to be $31.1% at 1 Sun (¼1 kW m À2, air mass 1.5), fundamentally limited by a matching photocurrent density of 25.3 mA cm À2 produced by the light absorbers. Choices of electrocatalysts, as well as the fill factors of the light absorbers and the Ohmic resistance of the solution electrolyte also play key roles in determining the maximum STH efficiency and the corresponding optimal tandem band gap combination. Pairing 1.6-1.8 eV band gap semiconductors with Si in a tandem structure produces promising light absorbers for water splitting, with theoretical STH efficiency limits of >25%. Broader contextAn integrated system that allows for the direct production of fuels from sunlight would provide a scalable, sustainable source of clean fuels for grid storage as well as for use in the transportation sector. Because all of the components of such a complete system must operate under mutually compatible conditions, an assessment of the required materials properties necessitates a systems-level analysis of the operational conditions of an integrated solar-fuel generator. Accordingly, the optimal system efficiency has been calculated for various solar-fuel generator system geometries and component dimensions, as a function of the band gaps of the light absorber components that serve to capture and convert sunlight into chemical fuels. Dual band gap light absorber congurations have been evaluated, with the dual band gap, tandem structure, providing optimal efficiency and thus a preferred approach, to effect direct solar-fuel production. The assessment has incorporated a variety of systems-level parameters that are present in an actual operating solar-fuel generator system, including the thermodynamic constraints on the light absorbers as given by the Shockley-Queisser detailed-balance limit, the overpotentials of earth-abundant catalysts for water oxidation and reduction reactions, and the effects of solution resistance and light absorber quality on the overall conversion process of sunlight into chemical fuels.

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Section: Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An analysis of the optimal band gaps of light absorbers in integrated tandem photoelectrochemical water-splitting systems

Xiang

Haussener

et al. 2013

Energy Environ. Sci.

530

545

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“…Dye-sensitization technique has a significant role in employing a visible fraction of the solar spectrum for water splitting application. Abe et al [37] reported the first example of overall water splitting in the presence of visible light using coumarin dyes (C343, and NKX-series (2677, 2697, 2311, 2587)) and metal oxide semiconductors. The oxidized forms of the dye molecules possess two or more thiophene rings in their structures and enjoy long lifespans to undergo reversible oxidation-reduction cycles.…”

Section: Review On Dye-sensitized Overall Water Splittingmentioning

confidence: 99%

Dye-Sensitized Photocatalytic Water Splitting and Sacrificial Hydrogen Generation: Current Status and Future Prospects

2017

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Today, global warming and green energy are important topics of discussion for every intellectual gathering all over the world. The only sustainable solution to these problems is the use of solar energy and storing it as hydrogen fuel. Photocatalytic and photo-electrochemical water splitting and sacrificial hydrogen generation show a promise for future energy generation from renewable water and sunlight. This article mainly reviews the current research progress on photocatalytic and photo-electrochemical systems focusing on dye-sensitized overall water splitting and sacrificial hydrogen generation. An overview of significant parameters including dyes, sacrificial agents, modified photocatalysts and co-catalysts are provided. Also, the significance of statistical analysis as an effective tool for a systematic investigation of the effects of different factors and their interactions are explained. Finally, different photocatalytic reactor configurations that are currently in use for water splitting application in laboratory and large scale are discussed.

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“…Additionally, electric power can be generated by a fuel cell using redox-reductant such as Fe 2+ . 8,9 Some reversible redox mediators such as Fe 3+/2+ , 1,2,4 IO 3 ¹ / I ¹ , 3,6,7 and NO 3 ¹ /NO 2 ¹ 5 have been reported for endergonic photocatalysis. We reported recently that Fe 3+ reduction and O 2 evolution for eq 1 reaction took place effectively over Csmodified WO 3 photocatalyst.…”

mentioning

confidence: 99%

Photocatalytic Energy Storage over Surface-modified WO3 Using V5+/V4+ Redox Mediator

2012

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Photocatalytic V 5+ reduction accompanied by O 2 evolution over WO 3 is reported for the first time. Water oxidation reaction utilizing VO 2 + ion as an electron acceptor proceeded photocatalytically over WO 3 . The activity of WO 3 was remarkably enhanced by the presence of Fe 3+/2+ ion at the ion-exchange site on WO 3 surface, and its apparent quantum yield (AQY) was 22% at 420 nm. Moreover, the AQY was raised to about 78% when a small amount of formic acid was added to reactant solution.Recently, photocatalytic water splitting utilizing two kinds of photocatalysts and a reversible redox mediator, which are similar to the photosynthesis mechanism (Z-scheme reaction) where two photoexcitation centers and many redox mediators are leveraged, has been attracting attention for solar energy conversion and storage. 17 When the redox potential of mediator is located between the water reduction and oxidation potentials (from 0 to 1.23 V vs. RHE), the redox-oxidant (Ox) reduction and water oxidation (eq 1) and redox-reductant (Red) oxidation and water reduction (eq 2) are endergonic reactions (Gibbs free energy, ¦G > 0), respectively.Moreover, photocatalysis of eq 1 is also useful for photocatalysiselectrolysis hybrid systems as practical water-splitting systems, where the reaction of eq 2 proceeds by electrolysis with a low applied bias ( Figure S1). 1,14 In this hybrid system, a simple and wide photocatalytic device, which is one of the most important features for effective solar energy utilization, can be easily made owing to stable storage of solar energy in the redox aqueous solution without a H 2 gas-tight cover over the photocatalytic device. Pure H 2 can be accumulated at the counter electrode chamber of electrolyzer anytime with low applied bias (nearly ¦G of eq 2). Additionally, electric power can be generated by a fuel cell using redox-reductant such as Fe 2+ . 8,9 Some reversible redox mediators such as Fe 3+/2+ , 1,2,4 IO 3 ¹ / I ¹ , 3,6,7 and NO 3 ¹ /NO 2 ¹ 5 have been reported for endergonic photocatalysis. We reported recently that Fe 3+ reduction and O 2 evolution for eq 1 reaction took place effectively over Csmodified WO 3 photocatalyst.1 However, the variety of reversible redox mediators is very limited and they have some problems, that is, pH range restriction, light shielding, solubility, stability, redox potential, and so on. Therefore, further development of candidate redox mediators has a great significance in view of the combination with various types of photocatalysts.In this study, we revealed for the first time that V 5+/4+ redox mediator can function as a redox reagent for the photocatalytic eq 1 reaction with a high quantum yield. Moreover, we clarified the activity of surface-modified WO 3 photocatalysts was significantly improved by coupling of V 5+/4+ with Fe 3+/2+ redox mediators. Although the effect of multiple redox combination on photocatalysis has been expected as a model reaction of artificial photosynthesis, the real demonstration of its positive effect has been difficult so far...

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Robust dye-sensitized overall water splitting system with two-step photoexcitation of coumarin dyes and metal oxide semiconductors

Abstract: Photocatalytic splitting of water into H2 and O2 under visible light irradiation is achieved using a coumarin dye-adsorbed lamellar niobium oxide for hydrogen evolution

Cited by 157 publications

References 19 publications

An analysis of the optimal band gaps of light absorbers in integrated tandem photoelectrochemical water-splitting systems

An analysis of the optimal band gaps of light absorbers in integrated tandem photoelectrochemical water-splitting systems

Dye-Sensitized Photocatalytic Water Splitting and Sacrificial Hydrogen Generation: Current Status and Future Prospects

Photocatalytic Energy Storage over Surface-modified WO3 Using V5+/V4+ Redox Mediator

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