Catalytic hydrogen production at cobalt centres

Losse, Sebastian; Vos, Johannes G.; Rau, Sven

doi:10.1016/j.ccr.2010.06.004

Cited by 297 publications

(234 citation statements)

References 55 publications

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“…This system also was found to function via reductive quenching of PS* by the electron donor, rather than by direct electron transfer from PS* to the catalyst or an electron mediator (37). A significant number of reviews provide detailed accounts of the various systems studied and their effectiveness with regard to H 2 generation (1,(58)(59)(60)(61)(62)(63)(64). However, all of them, which contain molecular light absorbers [charge transfer (CT) metal complexes and organic dyes], suffer from photoinstability during prolonged irradiation.…”

Section: Significancementioning

confidence: 99%

Photogeneration of hydrogen from water using CdSe nanocrystals demonstrating the importance of surface exchange

Das

Han

Haghighi

et al. 2013

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

130

139

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Unique tripodal S-donor capping agents with an attached carboxylate are found to bind tightly to the surface of CdSe nanocrystals (NCs), making the latter water soluble. Unlike that in similarly solubilized CdSe NCs with one-sulfur or two-sulfur capping agents, dissociation from the NC surface is greatly reduced. The impact of this behavior is seen in the photochemical generation of H 2 in which the CdSe NCs function as the light absorber with metal complexes in aqueous solution as the H 2 -forming catalyst and ascorbic acid as the electron donor source. This precious-metalfree system for H 2 generation from water using [Co(bdt) 2 ]− (bdt, benzene-1,2-dithiolate) as the catalyst exhibits excellent activity with a quantum yield for H 2 formation of 24% at 520 nm light and durability with >300,000 turnovers relative to catalyst in 60 h.photochemistry | solar energy | catalysis | water splitting | quantum dots A rtificial photosynthesis (AP) represents an important strategy for energy conversion from sunlight to storage in chemical bonds (1-4). Unlike natural photosynthesis in which CO 2 + H 2 O are converted into carbohydrates and O 2 , the key energy-storing reaction in AP is the splitting of water into its constituent elements of hydrogen and oxygen (5-16). As a redox reaction, water splitting can be divided into two half-reactions, of which the light-driven generation of H 2 is the reductive component. Many systems for the photogeneration of H 2 have been described over the years and they typically consist of a light absorber, a catalyst for H 2 formation, and sources of protons and electrons. For systems that function in aqueous media, the protons are provided by water, whereas for nonaqueous systems, the protons are provided by weak, generally organic acids. The source of electrons in these photochemical systems is generally a sacrificial electron donor-that is, a compound that decomposes following one electron oxidation.Reports of the light-driven generation of hydrogen date back more than 30 y, beginning with a multicomponent system containing [Ru(bpy) 3 ] 2+ (where bpy is 2,2′-bipyridine) as the chromophore or photosensitizer (PS) and colloidal Pt as the catalyst for making H 2 from protons and electrons (17). In these and many subsequent systems, electron mediators were used to accept an electron from the excited chromophore, PS*-thereby serving as an oxidative quencher-and transfer it to the catalyst. Whereas two of the initial mediators were bpy complexes of rhodium and cobalt (17, 18), the overwhelming majority of electron mediators in these systems were dialkylated 2,2′-and 4,4′-bipyridines and their derivatives (19)(20)(21)(22). The most extensively used of these mediators was methyl viologen (MV 2+ , dimethyl-4,4′-bipyridinium, usually as its chloride salt). These mediators were subsequently found to undergo deactivation in their role by hydrogenation (23, 24). The sacrificial electron donors used in these studies depended on system pH and were generally based on compounds having tertiary amine func...

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Section: Significancementioning

confidence: 99%

Photogeneration of hydrogen from water using CdSe nanocrystals demonstrating the importance of surface exchange

Das

Han

Haghighi

et al. 2013

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

130

139

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“…Route (ii) can be taken by screening properties of the catalytic system like solvent composition, pH value and ionic additives. 5,7,[23][24][25][26][27] Within this research, it has, for instance, been shown that the addition of N(C 4 H 9 ) 4 Cl to the photocatalytic system for the light induced formation of hydrogen from water based on [Ru(tbbpy) 2 (tpphz)-PdCl 2 ](PF 6 ) 2 (RutpphzPd) (ruthenium(II)-bis(4,4′-di-tert-butyl-2,2′-bipyridyl)-(μ-tetrapyrido[3,2-a:2′,3′-c:3″,2″-h:2′″,3′″-j]phenazine)-(dichloropalladium)-dihexafluorophosphate) ( Fig. 1) leads to a significant drop in catalytic activity.…”

Section: Introductionmentioning

confidence: 99%

Supramolecular activation of a molecular photocatalyst

et al. 2014

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“…This has triggered the development of catalysts based on earth-abundant 3d elements, such as cobalt, iron and nickel. [3][4][5][6][7][8] Cobaloximes are perspective and popular hydrogen evolving molecular catalysts [7][8][9] and they have been implemented in many homogeneous multicomponent photocatalytic systems. [7,[10][11][12][13][14][15][16] (Fig.…”

mentioning

confidence: 99%

Microsecond X‐ray Absorption Spectroscopy Identification of Co^I Intermediates in Cobaloxime‐Catalyzed Hydrogen Evolution

Smolentsev

Cecconi

Guda

et al. 2015

Chemistry A European J

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Rational development of efficient photo-catalytic systems for hydrogen production requires understanding the catalytic mechanism and detailed information about the structure of intermediates in the catalytic cycle. We demonstrate how time-resolved X-ray absorption spectroscopy in the microsecond time range can be used to identify such intermediates and to determine their local geometric structure. This method was used to obtain the solution structure of the Co(I) intermediate of cobaloxime, which is a non-noble metal catalyst for solar hydrogen production from water. Distances between cobalt and nearest ligands including two solvent molecules and displacement of the cobalt atom out of plane formed by the planar ligands have been determined. Combining in situ X-ray absorption and UV-visible data, we demonstrate how slight modification of the catalyst structure can lead to the formation of a catalytically inactive Co(I) state under similar conditions. Possible deactivation mechanisms are discussed. KeywordsTransient X-ray absorption; photocatalysis; XANES; X-ray absorption spectroscopy; solar fuel Light-driven catalytic systems for hydrogen evolution from water are crucial components of our energy future.[1,2] Efficient photo-catalytic hydrogen evolution systems contain platinum nanoparticles or other noble metals that are expensive and of limited availability. This has triggered the development of catalysts based on earth-abundant 3d elements, such as cobalt, iron and nickel. [3][4][5][6][7][8] Cobaloximes are perspective and popular hydrogen evolving molecular catalysts [7][8][9] and they have been implemented in many homogeneous multicomponent photocatalytic systems. [7,[10][11][12][13][14][15][16] (Fig. 1, top panel). In the absence of a sacrificial electron donor, charge recombination returns the system to its initial state. The solution structure of the Co(I) intermediate has been predicted using DFT, [17,20,22] but was never experimentally probed. A crystal structure of the Co(I) derivative [Co(dpgBF 2 ) 2 (CH 3 CN)] -has been reported, [18] but the structure of the intermediate in solution can be significantly different from those in the solid phase. Here, we combine in situ time-resolved X-ray absorption near edge structure (XANES) spectroscopy and UV-visible spectroscopy to investigate the early stages of hydrogen evolution mediated by Co1 and Co2 catalysts. We report the first experimental determination of the structure of the Co(I) intermediate formed from Co2 in solution and highlight a major difference in terms of reactivity and stability between Co2 and Co1 under photo-catalytic conditions.XANES spectra contain element-specific information about the structure of metal complexes.[23-25] Time-resolved X-ray absorption spectroscopy in the laser pump-X-ray probe mode was initially established for experiments in the picosecond -nanosecond time range [26,27]. We recently extended the technique to the microsecond range (pumpsequential-probes[28] and pump-flow-probe[29] methods, see SI). These new...

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Catalytic hydrogen production at cobalt centres

Cited by 297 publications

References 55 publications

Photogeneration of hydrogen from water using CdSe nanocrystals demonstrating the importance of surface exchange

Photogeneration of hydrogen from water using CdSe nanocrystals demonstrating the importance of surface exchange

Supramolecular activation of a molecular photocatalyst

Microsecond X‐ray Absorption Spectroscopy Identification of Co^I Intermediates in Cobaloxime‐Catalyzed Hydrogen Evolution

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Catalytic hydrogen production at cobalt centres

Cited by 297 publications

References 55 publications

Photogeneration of hydrogen from water using CdSe nanocrystals demonstrating the importance of surface exchange

Photogeneration of hydrogen from water using CdSe nanocrystals demonstrating the importance of surface exchange

Supramolecular activation of a molecular photocatalyst

Microsecond X‐ray Absorption Spectroscopy Identification of CoI Intermediates in Cobaloxime‐Catalyzed Hydrogen Evolution

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Product

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Microsecond X‐ray Absorption Spectroscopy Identification of Co^I Intermediates in Cobaloxime‐Catalyzed Hydrogen Evolution