An All‐Inorganic, Stable, and Highly Active Tetraruthenium Homogeneous Catalyst for Water Oxidation

Geletii, Yurii V.; Botar, Bogdan; Kögerler, Paul; Hillesheim, Daniel A.; Musaev, Djamaladdin G.; Hill, Craig L.

doi:10.1002/ange.200705652

Cited by 181 publications

(120 citation statements)

References 36 publications

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“…In the absence of an applied potential or without oxidants in solution, the calculations show that every Ru atom of the Ru 4 -POM is in oxidation state IV and coordinates a water ligand, thus resulting in four Ru(IV)-H 2 O groups ( Fig. 1A) (13,14,21). In this configuration, the d 4 electrons formally residing on the metal ion in the Ru(IV)-H 2 O moiety occupy the t 2g -like orbitals with two unpaired spins (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Although the thermodynamic efficiency of the Ru 4 -POM can be controlled by only one or two sites, the presence of multiple metal centers clearly plays an important function, as shown by the significantly superior performance of Ru 4 -POM (13,14) compared with the single center catalysts (34). The difference in their efficiency is likely to arise from the local environment around the active sites, shaped and reinforced by the metal-oxo connectivity among them.…”

Section: Atomistic and Thermodynamic Origins Of Catalytic Efficiency:mentioning

confidence: 99%

“…One of the most efficient and robust catalytic cores reported so far is a tetraruthenate oxo fragment [Ru 4 O 4 (OH) 2 (H 2 O) 4 ] 6+ sandwiched between two inert polyoxotungstate ligands [Ru 4 -POM; Fig. 1A], displaying a discrete and nano-sized structure.Ru 4 -POM has been shown to oxidize water in the homogeneous phase with small overpotential (0.35 eV), high turnover frequency (>450 h −1 ), and no degradation (13,14). By virtue of the molecular nature, when coupled to photogenerated oxidants, it displays photo-induced electron transfer rates in the nano/ microsecond time domain (15), thus approaching the natural paradigm, while preserving its activity also when it is interfaced with functionalized carbon nanotubes (16).…”

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Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium–oxo molecular complex

Piccinin

Sartorel

Aquilanti

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

106

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Solar-to-fuel energy conversion relies on the invention of efficient catalysts enabling water oxidation through low-energy pathways. Our aerobic life is based on this strategy, mastered by the natural Photosystem II enzyme, using a tetranuclear Mn-oxo complex as oxygen evolving center. Within artificial devices, water can be oxidized efficiently on tailored metal-oxide surfaces such as RuO 2 . The quest for catalyst optimization in vitro is plagued by the elusive description of the active sites on bulk oxides. Although molecular mimics of the natural catalyst have been proposed, they generally suffer from oxidative degradation under multiturnover regime. Here we investigate a nano-sized Ru 4 -polyoxometalate standing as an efficient artificial catalyst featuring a totally inorganic molecular structure with enhanced stability. Experimental and computational evidence reported herein indicates that this is a unique molecular species mimicking oxygenic RuO 2 surfaces. Ru 4 -polyoxometalate bridges the gap between homogeneous and heterogeneous water oxidation catalysis, leading to a breakthrough system. Density functional theory calculations show that the catalytic efficiency stems from the optimal distribution of the free energy cost to form reaction intermediates, in analogy with metal-oxide catalysts, thus providing a unifying picture for the two realms of water oxidation catalysis. These correlations among the mechanism of reaction, thermodynamic efficiency, and local structure of the active sites provide the key guidelines for the rational design of superior molecular catalysts and composite materials designed with a bottom-up approach and atomic control.artificial photosynthesis | ab initio simulations | X-ray absorption spectroscopy | electrocatalysis P hotocatalytic water splitting offers a bioinspired strategy for replacing fossil fuels with clean energy vectors (1-3). The overall reaction entails a sequence of light-promoted electron and proton transfers coupled with cleavage and formation of molecular bonds, ultimately splitting H 2 O molecules into O 2 and H 2 . The application of such technology for a viable solar-fuel economy is at the forefront of a very intense research effort. The main issue is the design and optimization of innovative catalysts enabling the half reaction of water oxidation (2H 2 O → O 2 + 4H + + 4e − ) (1) at low overpotential, high turnover frequencies, and longterm operation stability. Considering its high thermodynamic cost [E 0 = −1.23 V at pH = 0 vs. normal hydrogen electrode (NHE)] and mechanistic complexity, water oxidation catalysis (WOC) poses severe challenges for artificial photosynthesis applications.In plants, water oxidation is catalyzed by the Mn 4 CaO 4 oxygen evolving complex of Photosystem II (PSII) enzymes. The natural catalyst exhibits a functional asset of four redox active metal centers with adjacent μ-oxo bridges to enable water oxidation with a maximal turnover frequency of 400 s −1 per O 2 molecule (4). The drawback lies in the intrinsic weakness of the biol...

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Section: Resultsmentioning

confidence: 99%

Section: Atomistic and Thermodynamic Origins Of Catalytic Efficiency:mentioning

confidence: 99%

mentioning

confidence: 99%

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Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium–oxo molecular complex

Piccinin

Sartorel

Aquilanti

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

106

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“…Recently a new interesting idea was presented in which two inorganic (SiW 10 ) ligands were employed to stabilize a tetranuclear Ru complex. 113 A stabilizing effect of a clay matrix has also been reported.…”

Section: IVmentioning

confidence: 92%

Solar water-splitting into H2 and O2: design principles of photosystem II and hydrogenases

Lubitz¹,

Reijerse²,

Messinger³

2008

Energy Environ. Sci.

404

362

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This review aims at presenting the principles of water-oxidation in photosystem II and of hydrogen production by the two major classes of hydrogenases in order to facilitate application for the design of artificial catalysts for solar fuel production. W: Lubitz E: Reijerse J: Messinger W. Lubitz is director of the MPI for Bioinorganic Chemistry and a specialist in advanced EPR techniques. He has a strong interest in both water-splitting and hydrogen production. E. Reijerse is working on hydrogenases using FTIR and EPR/ENDOR spectroscopies. J. Messinger is analyzing photosynthetic and artificial water-splitting employing O 2 measurements, mass spectrometry (MIMS), EPR and XAS.

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“…1). Other catalysts based on iridium and ruthenium complexes and in rutheniumcontaining polyoxometalates have been reported recently (22)(23)(24)(25).…”

mentioning

confidence: 99%

Mediator-assisted water oxidation by the ruthenium “blue dimer”cis,cis-[(bpy)₂(H₂O)RuORu(OH₂)(bpy)₂]⁴⁺

Concepcion

Jurss

Templeton

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

117

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Light-driven water oxidation occurs in oxygenic photosynthesis in photosystem II and provides redox equivalents directed to photosystem I, in which carbon dioxide is reduced. Water oxidation is also essential in artificial photosynthesis and solar fuelforming reactions, such as water splitting into hydrogen and oxygen (2 H2O ؉ 4 h 3 O2 ؉ 2 H2) or water reduction of CO2 to methanol (2 H2O ؉ CO2 ؉ 6 h 3 CH3OH ؉ 3/2 O2), or hydrocarbons, which could provide clean, renewable energy. The ''blue ruthenium dimer,'' cis,cis-[(bpy)2(H2O)Ru III ORu III (OH2)(bpy)2] 4؉ , was the first well characterized molecule to catalyze water oxidation. On the basis of recent insight into the mechanism, we have devised a strategy for enhancing catalytic rates by using kinetically facile electron-transfer mediators. Rate enhancements by factors of up to Ϸ30 have been obtained, and preliminary electrochemical experiments have demonstrated that mediator-assisted electrocatalytic water oxidation is also attainable.catalysis ͉ redox mediator ͉ electron transfer W ater oxidation is a key reaction in photosynthesis, the basis for most of life as we know it (1-8). It is also a central reaction in artificial photosynthesis, an example being solardriven splitting of water into hydrogen and oxygen, 2 H 2 O 3 O 2 ϩ 2 H 2 (9-11). In natural photosynthesis, water oxidation occurs at photosystem II (PSII) through the Kok cycle after absorption of four photons. Detailed insight into how this reaction occurs is emerging on the basis of theoretical and spectroscopic studies and recent x-ray diffraction and extended x-ray absorption fine structure results to 3.0-Å resolution (12)(13)(14).Given the demands of the half reaction, 2 H 2 O 3 O 2 ϩ 4 H ϩ ϩ 4e Ϫ , with requirements for both 4e Ϫ /4H ϩ loss and OOO bond formation, water oxidation is difficult to achieve at a single catalyst site or cluster. In addition to PSII, water oxidation is also catalyzed by the ruthenium ''blue dimer'' cis,cis-[(bpy) 2 (H 2 O)Ru III ORu III (OH 2 )(bpy) 2 ] 4ϩ (bpy is 2,2Ј-bipyridine) and structurally related derivatives (15-21) (Fig. 1). Other catalysts based on iridium and ruthenium complexes and in rutheniumcontaining polyoxometalates have been reported recently (22-25).The low oxidation state Ru III -O-Ru III form of the ruthenium blue dimer undergoes oxidative activation by proton-coupled electron transfer (PCET) in which stepwise loss of electrons and protons occurs. PCET is essential, because it allows for the buildup of multiple oxidative equivalents at a single site or cluster without building up positive charge (21, 26). As shown by the results of pH-dependent electrochemical studies (16), loss of 4e Ϫ /4H ϩ occurs to give a reactive, transient intermediate followed by O 2 evolution.In the absence of a serendipitous discovery, mechanistic knowledge is required for the design of robust, long-lived catalysts for water oxidation. Such knowledge is also important for the microscopic reverse reaction, oxygen reduction to water, which occurs at the cathode (reducing e...

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An All‐Inorganic, Stable, and Highly Active Tetraruthenium Homogeneous Catalyst for Water Oxidation

Cited by 181 publications

References 36 publications

Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium–oxo molecular complex

Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium–oxo molecular complex

Solar water-splitting into H2 and O2: design principles of photosystem II and hydrogenases

Mediator-assisted water oxidation by the ruthenium “blue dimer”cis,cis-[(bpy)₂(H₂O)RuORu(OH₂)(bpy)₂]⁴⁺

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An All‐Inorganic, Stable, and Highly Active Tetraruthenium Homogeneous Catalyst for Water Oxidation

Cited by 181 publications

References 36 publications

Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium–oxo molecular complex

Water oxidation surface mechanisms replicated by a totally inorganic tetraruthenium–oxo molecular complex

Solar water-splitting into H2 and O2: design principles of photosystem II and hydrogenases

Mediator-assisted water oxidation by the ruthenium “blue dimer”cis,cis-[(bpy)2(H2O)RuORu(OH2)(bpy)2]4+

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Mediator-assisted water oxidation by the ruthenium “blue dimer”cis,cis-[(bpy)₂(H₂O)RuORu(OH₂)(bpy)₂]⁴⁺