Design Considerations for a System for Photocatalytic Hydrogen Production from Water Employing Mixed-Metal Photochemical Molecular Devices for Photoinitiated Electron Collection

Arachchige, Shamindri M.; Brown, Jared R.; Chang, Eric L.; Jain, Avijita; Zigler, David F.; Rangan, Krishnan; Brewer, Karen J.

doi:10.1021/ic8017387

Cited by 97 publications

(83 citation statements)

References 44 publications

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“…Second, a nonconjugated bridging ligand should be used because a conjugated system in the bridge ligand lowers the reducing power of the catalyst unit (9). The efficiencies and the stability of these supramolecular photocatalysts (Φ CO ¼ 0.12-0.15, TON CO ∼ 200) are much greater than those of the other reported supramolecular-type photocatalysts for both CO 2 reduction (13-16) and H 2 evolution (16)(17)(18)(19). We sought to apply this architecture to construct unique supramolecular photocatalysts for the reduction of CO 2 to selectively form formic acid (which has not been reported to date).…”

mentioning

confidence: 99%

Photocatalytic CO ₂ reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes

Tamaki

Morimoto

Koike

et al. 2012

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

308

238

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Previously undescribed supramolecules constructed with various ratios of two kinds of Ru(II) complexes-a photosensitizer and a catalyst-were synthesized. These complexes can photocatalyze the reduction of CO 2 to formic acid with high selectivity and durability using a wide range of wavelengths of visible light and NADH model compounds as electron donors in a mixed solution of dimethylformamide-triethanolamine. Using a higher ratio of the photosensitizer unit to the catalyst unit led to a higher yield of formic acid. In particular, of the reported photocatalysts, a trinuclear complex with two photosensitizer units and one catalyst unit photocatalyzed CO 2 reduction (Φ HCOOH ¼ 0.061, TON HCOOH ¼ 671) with the fastest reaction rate (TOF HCOOH ¼ 11.6 min −1 ). On the other hand, photocatalyses of a mixed system containing two kinds of model mononuclear Ru(II) complexes, and supramolecules with a higher ratio of the catalyst unit were much less efficient, and black oligomers and polymers were produced from the Ru complexes during photocatalytic reactions, which reduced the yield of formic acid. The photocatalytic formation of formic acid using the supramolecules described herein proceeds via two sequential processes: the photochemical reduction of the photosensitizer unit by NADH model compounds and intramolecular electron transfer to the catalyst unit. R ecently, global warming and shortages of fossil fuels and carbon resources have become serious issues. The development of technologies to convert CO 2 into useful organic compounds using sunlight as an energy source would serve as an ideal solution to these problems.Formic acid, which is the two-electron reduction product of CO 2 , has recently attracted attention as a storage source of H 2 (1, 2). Formic acid itself is an important chemical. It has been employed as a preservative and an insecticide and is also a useful acid, reducing agent, and source of carbon in synthetic chemical industries.Only a few photocatalysts for the selective formation of formic acid from CO 2 have been reported (3-8). Although oligo(p-phenylenes) (3) or a mixed system of phenazine and Co cyclam (4) successfully photocatalyzed the reduction of CO 2 to formic acid, these systems cannot work with visible light. It has been reported that ½RuðbpyÞ 2 ðCOÞ 2 2þ (bpy ¼ 2,2′-bipyridine) acted as a catalyst for reducing CO 2 (5-8). Under basic conditions, a mixed system of this complex with ½RuðbpyÞ 3 2þ as a redox photosensitizer photocatalyzed the reduction of CO 2 to formic acid with high selectivity (6, 8). However, this photocatalytic system is limited by instability as evidenced by the fact that the catalyst decomposed following prolonged irradiation and generated black precipitates.We have recently developed a unique architecture for constructing visible-light-driven supramolecular photocatalysts, consisting of a ½RuðN ∧ NÞ 3 2þ (N ∧ N ¼ a diimine ligand)-type complex as a photosensitizer and a Re(I) diimine complex as a catalyst (9-12). These supramolecules can selectively photocatalyze ...

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confidence: 99%

Photocatalytic CO ₂ reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes

Tamaki

Morimoto

Koike

et al. 2012

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

308

238

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“…[13][14][15] The bridging ligand between Ru and Rh metals in this case was 2,3-bis(2-pyridyl)pyrazine (dpp) to result in the [(bpy) 2 Ru(dpp)BrRhBr(dpp) Ru(bpy) 2 ] 5+ molecular construct shown in Fig. 1b.…”

Section: A Few Specific Case Studies Of Photoinduced Charge Accumulationmentioning

confidence: 99%

Photoinduced Charge Accumulation in Molecular Systems

Bonn

Wenger²

2015

Chimia

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Fuel-forming reactions such as CO 2 reduction or water splitting require multiple redox equivalents. When aiming at light-driven production of energy-rich chemicals, nowadays often referred to as solar fuels, it therefore becomes important to master the photoinduced accumulation of electrons or holes on individual molecular components. Featured in this short review are some of the key molecular systems explored in this emerging field of research. This includes for example a trinuclear Ru(ii)-Rh(iii)-Ru(iii) complex or an Ir(iii)-sensitized polyoxotungstate hybrid, but also several systems in which electron or hole collection occurs at organic moieties such as perylenebis(dicarboximide), quinone-containing or oligotriarylamine-based units. In many cases the photodriven accumulation of charge requires the use of sacrificial electron donors, but there exist also a handful of studies in which redox equivalents can be accumulated without the use of such additives.

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“…Electrochemically the trimetallic complexes of the general formula [{(TL) 2 3+ shows irreversible Rh III/II/I reductions at −0.51 and −0.55 V vs SCE (M, Ru or Os), respectively, followed by dpp 0/− couples for each dpp. 42 The lower cationic charge and the presence of more electron-rich TLs in the tpy-based systems shifts the Rh III/II/I reduction to more negative potentials. The electrochemistry of the trimetallic supramolecular complexes predicts an Ru(dπ)-or Os(dπ)-HOMO with energy tuned by the TL or LA metal and an Rh(dσ * )-based LUMO with energy tuned by the halides.…”

Section: Rhodium-based Supramolecular Photocatalysts: Redox Propertiesmentioning

confidence: 99%

“…42 A thermodynamically favorable driving force for reductive quenching of the 3 MLCT state by DMA exists for [{(bpy) 2 Ru(dpb)} 2 IrCl 2 ] 5+ , as the excited state reduction potential of the 3 MLCT is 1.13 V vs SCE. This iridium-based complex is not a photocatalyst under the conditions studied for the other systems.…”

Section: 67mentioning

confidence: 99%

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Hydrogen Production from Water: Photocatalysis

Arachchige

Brewer

2005

Encyclopedia of Inorganic Chemistry

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Photocatalytic hydrogen production from water provides an attractive but challenging approach to meeting our global energy needs. Design and development of systems that utilize visible light to drive the energetically favorable, multielectron reduction of water to produce hydrogen fuel have been of long‐term interest. Addressing the challenges of efficient harvesting of solar energy to produce transportable fuels requires ongoing, sustained research in this field. Current technologies utilize photobiological methods, photoelectrochemical methods, and molecular photocatalysis. This article focuses on the recent progress of proton or water reduction using supramolecular photocatalysts. These photochemical molecular devices often couple charge‐transfer light absorbers (LAs) to reactive metals in complex molecular architectures. Linking multiple components into large molecular assemblies allows for applications requiring complex functions. Early successes in supramolecular photocatalysts for solar hydrogen production are summarized. The redox, excited state properties, and photochemical properties of supramolecular systems applicable in photocatalytic hydrogen production are presented. Fundamental studies of the perturbations of subunit properties upon incorporation into supramolecular arrays are paramount to their successful application in this forum. Optical excitation typically affords a metal‐to‐ligand charge‐transfer state that is quenched by electron transfer, providing reduced complexes with reactive metals able to deliver the electrons to substrates. Sacrificial electron donors provide coupling to oxidative chemistry, allowing independent study of photocatalysts and hydrogen production schemes. Supramolecular chemistry allows modulation of redox, photophysical, and photochemical properties by component modification. Coupling multiple LAs to an electron acceptor, which, when reduced by multiple electrons, provides photoinitiated electron collectors (ECs). Photoinitiated ECs, which collect multiple electrons on a reactive rhodium center with the supramolecular architecture remaining, reduce water to hydrogen fuel. Mixed‐valence systems that promote HX reduction to produce hydrogen have also been described. Coupling of charge‐transfer LAs to cobalt, iron, palladium, or platinum is a topic of recent interest in the design of water reduction photocatalysts. The general design considerations for the development of supramolecular assemblies that function as photocatalysts for proton reduction are discussed, providing valuable insight into engineering efficient solar hydrogen production catalysts for water reduction. Mechanistic studies remain important to understanding this complex multielectron photochemistry, which will aid in future molecular design. Much remains to be mastered in this complicated, multielectron photochemistry but recently there is increased awareness and interest in this field.

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Design Considerations for a System for Photocatalytic Hydrogen Production from Water Employing Mixed-Metal Photochemical Molecular Devices for Photoinitiated Electron Collection

Cited by 97 publications

References 44 publications

Photocatalytic CO ₂ reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes

Photocatalytic CO ₂ reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes

Photoinduced Charge Accumulation in Molecular Systems

Hydrogen Production from Water: Photocatalysis

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Design Considerations for a System for Photocatalytic Hydrogen Production from Water Employing Mixed-Metal Photochemical Molecular Devices for Photoinitiated Electron Collection

Cited by 97 publications

References 44 publications

Photocatalytic CO 2 reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes

Photocatalytic CO 2 reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes

Photoinduced Charge Accumulation in Molecular Systems

Hydrogen Production from Water: Photocatalysis

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Photocatalytic CO ₂ reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes

Photocatalytic CO ₂ reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes