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

Concepcion, Javier J.; Jurss, Jonah W.; Templeton, Joseph L.; Meyer, Thomas J.

doi:10.1073/pnas.0807153105

Cited by 116 publications

(85 citation statements)

References 45 publications

(55 reference statements)

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“…Both protonated and deprotonated form of the intermediate are directly observed by pairs of optical absorptions at 451, 750 nm and 482, 850 nm, respectively [50,51]. This hydroperoxide forming step (1) [52,53].…”

Section: Molecular Metalmentioning

confidence: 99%

Towards a Molecular Level Understanding of the Multi-Electron Catalysis of Water Oxidation on Metal Oxide Surfaces

Zhang

Frei

2014

Catal Lett

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Earth abundant metal oxides play a central role as catalysts in the essential chemical transformations of sunlight to fuel conversion, which are the oxidation of water and the reduction of carbon dioxide. The rapidly growing interest in renewable fuel generation by using the energy of the sun has recently led to substantial breakthroughs in the use of first row transition metal oxides as catalysts for oxygen evolution from water. Substantive improvements of rates and lowering of overpotentials have been achieved by exploiting materials properties on the nanoscale, or taking advantage of the synergy of multiple metals. Moreover, knowledge derived from mechanistic investigations with structure specific spectroscopy is accelerating efficiency improvements. Monitoring by timeresolved FT-infrared spectroscopy reveals the molecular nature of active sites, while in situ X-ray and optical spectroscopy under reaction conditions provides insights into the electronic structure of the surface metal centers participating in the catalysis. By combining the bond specificity of vibrational spectroscopy with the metal electronic structure specificity of optical, X-ray absorption or photoelectron spectroscopy, a complete understanding of active surface sites on metal oxides begins to emerge. Charge flow driving the chemical transformations probed by optical spectroscopy across time scales from ultrafast to very slow reveals the processes that control the productive use of charges delivered to the catalyst. Coupling of the water oxidation catalysis at a metal oxide catalyst with carbon dioxide reduction at a heterobinuclear chromophore, which is the goal of the artificial photosystem approach, is demonstrated by a well-defined all-inorganic polynuclear unit.

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Section: Molecular Metalmentioning

confidence: 99%

Towards a Molecular Level Understanding of the Multi-Electron Catalysis of Water Oxidation on Metal Oxide Surfaces

Zhang

Frei

2014

Catal Lett

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“…As noted above (see Figure 1), water oxidation catalysts must deliver electrons to oxidized photosensitizer molecules rapidly, because the time scale for back electron transfer is fast, typically microseconds to milliseconds. Despite much recent progress in the design of molecular water oxidation catalysts, [33][34][35][36][37][38][39] such fast turnover rates have not been achieved.…”

Section: Catalysis Of the Water Oxidation Reactionmentioning

confidence: 99%

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

et al. 2009

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R esearchers are intensively investigating photochemical water splitting as a means of converting solar to chemical energy in the form of fuels. Hydrogen is a key solar fuel because it can be used directly in combustion engines or fuel cells, or combined catalytically with CO 2 to make carbon containing fuels. Different approaches to solar water splitting include semiconductor particles as photocatalysts and photoelectrodes, molecular donor-acceptor systems linked to catalysts for hydrogen and oxygen evolution, and photovoltaic cells coupled directly or indirectly to electrocatalysts.Despite several decades of research, solar hydrogen generation is efficient only in systems that use expensive photovoltaic cells to power water electrolysis. Direct photocatalytic water splitting is a challenging problem because the reaction is thermodynamically uphill. Light absorption results in the formation of energetic charge-separated states in both molecular donor-acceptor systems and semiconductor particles. Unfortunately, energetically favorable charge recombination reactions tend to be much faster than the slow multielectron processes of water oxidation and reduction. Consequently, visible light water splitting has only recently been achieved in semiconductor-based photocatalytic systems and remains an inefficient process.This Account describes our approach to two problems in solar water splitting: the organization of molecules into assemblies that promote long-lived charge separation, and catalysis of the electrolysis reactions, in particular the four-electron oxidation of water. The building blocks of our artificial photosynthetic systems are wide band gap semiconductor particles, photosensitizer and electron relay molecules, and nanoparticle catalysts. We intercalate layered metal oxide semiconductors with metal nanoparticles. These intercalation compounds, when sensitized with [Ru(bpy) 3 ] 2+ derivatives, catalyze the photoproduction of hydrogen from sacrificial electron donors (EDTA 2-) or non-sacrificial donors (I -). Through exfoliation of layered metal oxide semiconductors, we construct multilayer electron donor-acceptor thin films or sensitized colloids in which individual nanosheets mediate light-driven electron transfer reactions. When sensitizer molecules are "wired" to IrO 2 · nH 2 O nanoparticles, a dye-sensitized TiO 2 electrode becomes the photoanode of a water-splitting photoelectrochemical cell.Although this system is an interesting proof-of-concept, the performance of these cells is still poor (∼1% quantum yield) and the dye photodegrades rapidly. We can understand the quantum efficiency and degradation in terms of competing kinetic pathways for water oxidation, back electron transfer, and decomposition of the oxidized dye molecules. Laser flash photolysis experiments allow us to measure these competing rates and, in principle, to improve the performance of the cell by changing the architecture of the electron transfer chain.

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“…Multistep electron transfer is used in many biological systems, including photosynthesis, to control the kinetics of oxidation-reduction reactions. It has been noted that biology prefers to use distance rather than free energy differences to tune electron transfer rates because the former is sufficient and the latter is too expensive in terms of energy efficiency (15).The four-electron oxidation of water is a kinetically demanding process that occurs on the millisecond timescale in the oxygenevolving complex (OEC) of Photosystem II as well as in a number of synthetic catalysts (16)(17)(18)(19)(20). A key component of Photosystem II is the tyrosine-histidine pair that mediates electron transfer between the OEC and P680…”

mentioning

confidence: 99%

“…The four-electron oxidation of water is a kinetically demanding process that occurs on the millisecond timescale in the oxygenevolving complex (OEC) of Photosystem II as well as in a number of synthetic catalysts (16)(17)(18)(19)(20). A key component of Photosystem II is the tyrosine-histidine pair that mediates electron transfer between the OEC and P680…”

mentioning

confidence: 99%

Improving the efficiency of water splitting in dye-sensitized solar cells by using a biomimetic electron transfer mediator

Zhao

Swierk

Megiatto

et al. 2012

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

287

276

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Photoelectrochemical water splitting directly converts solar energy to chemical energy stored in hydrogen, a high energy density fuel. Although water splitting using semiconductor photoelectrodes has been studied for more than 40 years, it has only recently been demonstrated using dye-sensitized electrodes. The quantum yield for water splitting in these dye-based systems has, so far, been very low because the charge recombination reaction is faster than the catalytic four-electron oxidation of water to oxygen. We show here that the quantum yield is more than doubled by incorporating an electron transfer mediator that is mimetic of the tyrosine-histidine mediator in Photosystem II. The mediator molecule is covalently bound to the water oxidation catalyst, a colloidal iridium oxide particle, and is coadsorbed onto a porous titanium dioxide electrode with a Ruthenium polypyridyl sensitizer. As in the natural photosynthetic system, this molecule mediates electron transfer between a relatively slow metal oxide catalyst that oxidizes water on the millisecond timescale and a dye molecule that is oxidized in a fast light-induced electron transfer reaction. The presence of the mediator molecule in the system results in photoelectrochemical water splitting with an internal quantum efficiency of approximately 2.3% using blue light.artificial photosynthesis | photoelectrochemistry T he design of biomimetic systems for artificial photosynthesis is of fundamental interest in the study of light-driven electron and proton transfer reactions. It also represents a potential route to the efficient conversion of solar energy to energy stored in fuel. System modeling has shown that it should be possible, using complementary dye molecules that absorb in the infrared and the visible, to construct artificial Z-schemes that split water with over 10% energy conversion efficiency (1, 2). It is simpler in many ways to design small molecules with the proper photoredox properties than it is to find a set of semiconductors that can be coupled for visible light water splitting. Nevertheless, the molecular approach has so far lagged behind the semiconductor-based approach where high efficiencies have been realized with expensive materials (3-7).A ubiquitous problem in molecular artificial photosynthesis is back electron transfer, which rapidly thermalizes the energy stored by light-induced charge separation in donor-acceptor pairs. Recently, our group and several others have studied this problem in dye-sensitized solar cells where a molecular dye and a porous TiO 2 electrode act as the donor-acceptor dyad (8-13). The dye is covalently coupled to a colloidal or molecular water oxidation catalyst. Fast back electron transfer, relative to the rate of water oxidation, results in low quantum yields for water splitting in these systems.It is well known that charge-separation lifetimes in molecular donor-acceptor systems can be increased dramatically by adding secondary electron donors or acceptors to form triads, tetrads, and more complex supermolecu...

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

Cited by 116 publications

References 45 publications

Towards a Molecular Level Understanding of the Multi-Electron Catalysis of Water Oxidation on Metal Oxide Surfaces

Towards a Molecular Level Understanding of the Multi-Electron Catalysis of Water Oxidation on Metal Oxide Surfaces

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

Improving the efficiency of water splitting in dye-sensitized solar cells by using a biomimetic electron transfer mediator

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