A Hybrid Photocatalytic System Comprising ZnS as Light Harvester and an [Fe<sub>2</sub>S<sub>2</sub>] Hydrogenase Mimic as Hydrogen Evolution Catalyst

Wen, Fan; Wang, Xiuli; Huang, Lei; Ma, Guijun; Yang, Jinhui; Li, Can

doi:10.1002/cssc.201200190

Cited by 101 publications

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“…As compared with those reported in the literature [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] , the durability and activity of the present system are greatly increased; possibly as a result of the stabilization of the components by chitosan confinement leading to consecutive multi-step electron transfer in equilibrium. The importance of the stabilization was also analysed by exchanging chitosan for relatively small and loose aggregates, anionic SDS (0.166 mol l À 1 ) and cationic CTAB (0.055 mol l À 1 , cetyl trimethyl ammonium bromide) micelles 37 .…”

Section: Discussionsupporting

confidence: 48%

“…From a photochemical point of view, the electron transfer is triggered by the absorption of a photon by a photosensitizer [13][14][15][16][17][18][19][20][21][22][23][24][25] . Since the first attempt by Sun and Åkermark 34 to construct an artificial photocatalytic system for H 2 evolution in 2003, a large number of synthetic model complexes have been pursued to mimic the structure and functionality of the diiron subunit of the natural [FeFe]-H 2 ase H-cluster [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] . It is encouraging to see that the catalytic efficiency for H 2 evolution from artificial photocatalytic systems using mimics of the diiron subsite of [FeFe]-H 2 ase as catalysts has been increased from null to more than hundreds or thousands of turnover numbers (TON) under different irradiation conditions.…”

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Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

et al. 2013

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Nature has created [FeFe]-hydrogenase enzyme as a hydrogen-forming catalyst with a high turnover rate. However, it does not meet the demands of economically usable catalytic agents because of its limited stability and the cost of its production and purification. Synthetic chemistry has allowed the preparation of remarkably close mimics of [FeFe]-hydrogenase but so far failed to reproduce its catalytic activity. Most models of the active site represent mimics of the inorganic cofactor only, and the enzyme-like reaction that proceeds within restricted environments is less well understood. Here we report that chitosan, a natural polysaccharide, improves the efficiency and durability of a typical mimic of the diiron subsite of [FeFe]-hydrogenase for photocatalytic hydrogen evolution. The turnover number of the self-assembling system increases B4,000-fold compared with the same system in the absence of chitosan. Such significant improvements to the activity and stability of artificial [FeFe]-hydrogenase-like systems have, to our knowledge, not been reported to date.

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Section: Discussionsupporting

confidence: 48%

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Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

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“…The results show that biomimetic molecular catalysts display high activities even fabricated in the inorganic photocatalytic system. Recently, this model was extended to hydrogenase mimic [(μ-SPh-4-NH 2 ) 2 Fe 2 (CO) 6 ] (referred to as [Fe 2 S 2 ]) as the cocatalyst for H 2 evolution, when semiconductor (ZnS) acts as a lightharvester and H 2 A as the electron donor [25]. Photocatalytic H 2 production with more than 2607 turnovers (based on [Fe 2 S 2 ]) and an initial turnover frequency of 100 h −1 can be achieved through the efficient transfer of photogenerated electrons from ZnS to [Fe 2 S 2 ] complex.…”

Section: Results and Discussion (A) Noble Metals As Reduction Cocatalmentioning

confidence: 99%

Roles of cocatalysts in semiconductor-based photocatalytic hydrogen production

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Yan

Zong

et al. 2013

Phil. Trans. R. Soc. A.

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A photocatalyst is defined as a functional composite material with three components: photo-harvester (e.g. semiconductor), reduction cocatalyst (e.g. for hydrogen evolution) and oxidation cocatalyst (e.g. for oxidation evolution from water). Loading cocatalysts on semiconductors is proved to be an effective approach to promote the charge separation and transfer, suppress the charge recombination and enhance the photocatalytic activity. Furthermore, the photocatalytic performance can be significantly improved by loading dual cocatalysts for reduction and oxidation, which could lower the activation energy barriers, respectively, for the two half reactions. A quantum efficiency (QE) as high as 93 per cent at 420 nm for H 2 production has been achieved for Pt–PdS/CdS, where Pt and PdS, respectively, act as reduction and oxidation cocatalysts and CdS as a photo-harvester. The dual cocatalysts work synergistically and enhance the photocatalytic reaction rate, which is determined by the slower one (either reduction or oxidation). This work demonstrates that the cocatalysts, especially the dual cocatalysts for reduction and oxidation, are crucial and even absolutely necessary for achieving high QEs in photocatalytic hydrogen production, as well as in photocatalytic water splitting.

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“…12 Remarkably, photocatalytic H 2 production with more than 2600 turnover numbers (based on [Fe 2 S 2 ]) and an initial TOF of 100 h À1 were achieved. Photoluminescence spectra showed that the addition of [Fe 2 S 2 ] catalyst dramatically quenches both the band-edge emission and the surface trap-state emission of ZnS, while the fluorescence intensity becomes weaker when the amount of [Fe 2 S 2 ] added was increased.…”

Section: Cocatalysts For Water Reduction Half Reactionmentioning

confidence: 97%

Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis

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S ince the 1970s, splitting water using solar energy has been a focus of great attention as a possible means for converting solar energy to chemical energy in the form of clean and renewable hydrogen fuel. Approaches to solar water splitting include photocatalytic water splitting with homogeneous or heterogeneous photocatalysts, photoelectrochemical or photoelectrocatalytic (PEC) water splitting with a PEC cell, and electrolysis of water with photovoltaic cells coupled to electrocatalysts. Though many materials are capable of photocatalytically producing hydrogen and/or oxygen, the overall energy conversion efficiency is still low and far from practical application. This is mainly due to the fact that the three crucial steps for the water splitting reaction: solar light harvesting, charge separation and transportation, and the catalytic reduction and oxidation reactions, are not efficient enough or simultaneously. Water splitting is a thermodynamically uphill reaction, requiring transfer of multiple electrons, making it one of the most challenging reactions in chemistry.This Account describes the important roles of cocatalysts in photocatalytic and PEC water splitting reactions. For semiconductor-based photocatalytic and PEC systems, we show that loading proper cocatalysts, especially dual cocatalysts for reduction and oxidation, on semiconductors (as light harvesters) can significantly enhance the activities of photocatalytic and PEC water splitting reactions. Loading oxidation and/or reduction cocatalysts on semiconductors can facilitate oxidation and reduction reactions by providing the active sites/reaction sites while suppressing the charge recombination and reverse reactions. In a PEC water splitting system, the water oxidation and reduction reactions occur at opposite electrodes, so cocatalysts loaded on the electrode materials mainly act as active sites/reaction sites spatially separated as natural photosynthesis does. In both cases, the nature of the loaded cocatalysts and their interaction with the semiconductor through the interface/junction are important. The cocatalyst can provide trapping sites for the photogenerated charges and promote the charge separation, thus enhancing the quantum efficiency; the cocatalysts could improve the photostability of the catalysts by timely consuming of the photogenerated charges, particularly the holes; most importantly, the cocatalysts catalyze the reactions by lowering the activation energy. Our research shows that loading suitable dual cocatalysts on semiconductors can significantly increase the photocatalytic activities of hydrogen and oxygen evolution reactions, and even make the overall water splitting reaction possible. All of these findings suggest that dual cocatalysts are necessary for developing highly efficient photocatalysts for water splitting reactions.

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A Hybrid Photocatalytic System Comprising ZnS as Light Harvester and an [Fe₂S₂] Hydrogenase Mimic as Hydrogen Evolution Catalyst

Cited by 101 publications

References 50 publications

Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

Roles of cocatalysts in semiconductor-based photocatalytic hydrogen production

Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis

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A Hybrid Photocatalytic System Comprising ZnS as Light Harvester and an [Fe2S2] Hydrogenase Mimic as Hydrogen Evolution Catalyst

Cited by 101 publications

References 50 publications

Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

Chitosan confinement enhances hydrogen photogeneration from a mimic of the diiron subsite of [FeFe]-hydrogenase

Roles of cocatalysts in semiconductor-based photocatalytic hydrogen production

Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis

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A Hybrid Photocatalytic System Comprising ZnS as Light Harvester and an [Fe₂S₂] Hydrogenase Mimic as Hydrogen Evolution Catalyst