Water Oxidation at a Tetraruthenate Core Stabilized by Polyoxometalate Ligands: Experimental and Computational Evidence To Trace the Competent Intermediates

Sartorel, Andrea; Miró, Pere; Salvadori, Enrico; Romain, Sophie; Carraro, Mauro; Scorrano, Gianfranco; Valentin, Marilena Di; Llobet, Antoni; Bó, Carles; Bonchio, Marcella

doi:10.1021/ja905067u

Cited by 197 publications

(169 citation statements)

References 27 publications

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“…3 (cycle A, S 0 − S 4 ). The calculated values of the free energy differences (ΔG) are in very good agreement with the available experimental data (black circles) (Note that only the S 0 −S 3 portion of the cycle is accessible experimentally) (19). This validates the high accuracy of the present computational approach [Becke 3 Lee Yang Parr (B3LYP) functional] for predicting the reaction thermodynamics.…”

Section: Resultssupporting

confidence: 83%

“…Moreover, the absence of adventitious Ru(III) species and or mixed valence states is evident from the position of the first absorption edge and from the line shape of the first absorption peak [note that in Ru(III)POM, the first structure is higher than the second one]. This is consistent with a silent EPR behavior of the freshly isolated crystals (19).…”

Section: Resultssupporting

confidence: 67%

See 1 more Smart Citation

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.

Self Cite

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: Resultssupporting

confidence: 83%

Section: Resultssupporting

confidence: 67%

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.

Self Cite

106

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“…[46b, 88,90] The aqua derivative has been subjected to intense examination because it proved to be an active and efficient catalyst for water oxidation to dioxygen proceeding via the Ru 4 (V,V,V,V) intermediate. Under acidic conditions with Ce IV as oxidant the turnover frequency (TOF) was 450 h À1 with a yield of 90 % with respect to the amount of oxidant.…”

Section: Rutheniummentioning

confidence: 99%

“…Under acidic conditions with Ce IV as oxidant the turnover frequency (TOF) was 450 h À1 with a yield of 90 % with respect to the amount of oxidant. [88,90] At pH 7 using electrochemically regenerated [Ru(bpy) 3 ] 3+ (bpy = bipyridine) the dioxygen yield varied with the amount of catalyst present, with a maximum yield of about 75 %. [87] There is considerable current research activity aimed at optimizing strategies of incorporating the Ru 4 -POM into efficient devices for water oxidation and other applications.…”

Section: Rutheniummentioning

confidence: 99%

Noble Metals in Polyoxometalates

2012

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Polyoxometalates containing noble metal ions, such as ruthenium, osmium, rhodium, palladium, platinum, silver and gold, are a structurally diverse class of compounds. They include both classical heteropolyanions (vanadates, molybdates, tungstates) in which noble metals are present as heteroatoms, as well as the recently discovered class of polyoxometalates with noble metal "addenda" atoms. The focus of this Review is on complexes that should, in principle, exist as discrete molecular species in solution, and which are therefore of interest for their reactivity, their future synthetic utility and potential applications, for example, in catalysis or nanoscience.

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“…Citing just a small portion of the broad interest in molecular water oxidation: ruthenium dimers [9][10][11][12] and tetramers, [13][14][15] cobalt tetramers, 16,17 manganese dimers 18 along with recent work detailing single-site catalysts [19][20][21][22][23][24][25][26] all illustrate the diversity of successful catalysts. More recently, a variety of Cp*Ir complexes (Cp* = C 5 Me 5 -) have been shown to act as efficient water oxidation precatalysts.…”

Section: Introductionmentioning

confidence: 99%

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

Woods

Lalrempuia

Petronilho

et al. 2014

Energy Environ. Sci.

107

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Iridium complexes of Cp* and mesoionic carbene ligands were synthesized and evaluated as potential water oxidation catalysts using cerium ammonium nitrate as a chemical oxidant. Performance was evaluated by turnover frequency at 50% conversion and by absolute turnover number, and the most promising precatalysts were subjected to further study. Molecular turnover frequencies varied from 190 to 451 per hour with a maximum turnover number of 38,000. While the rate of oxygen evolution depends linearly on iridium concentration, 10 concurrent spectroscopic and manometric monitoring of stoichiometric additions of oxidant suggests oxygen evolution occurs as two sequential first order reactions. Under the conditions herein, the oxygen evolving species appears to be well defined and molecular based on the kinetic effects of careful ligand design, reproducibility, and the absence of persistent dynamic light scattering signals. Outside of these conditions, the complex mechanism is highly dependent on reaction conditions. While confident characterization of the catalytically active species is difficult, especially under high-turnover conditions, this work indicates IrOx is not essential for the 15 formation of catalytically active water oxidation species.

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Water Oxidation at a Tetraruthenate Core Stabilized by Polyoxometalate Ligands: Experimental and Computational Evidence To Trace the Competent Intermediates

Cited by 197 publications

References 27 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

Noble Metals in Polyoxometalates

Carbene iridium complexes for efficient water oxidation: scope and mechanistic insights

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