Efficient electrocatalytic hydrogen production from H+ ions using specially designed boron-capped cobalt clathrochelates

Voloshin, Yan Z.; Dolganov, Alexander V.; Varzatskii, Оleg А.; Bubnov, Yurii N.

doi:10.1039/c1cc12239h

Cited by 86 publications

(50 citation statements)

References 34 publications

(7 reference statements)

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“…This concept is challenging to put into practice, however, as incorporation of a redox-active ligand can have detrimental effects. For example, the delocalization of spin onto the ligand framework in Co-bisglyoxime 39,40,42 and trisglyoxime 66 catalysts have been shown to promote ligand hydrogenation 67−70 during catalysis, significantly reducing catalyst longevity.…”

Section: ■ Redox-active Ligands For Redox-leveling and Facilitating Mmentioning

confidence: 99%

Metal–Polypyridyl Catalysts for Electro- and Photochemical Reduction of Water to Hydrogen

et al. 2015

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CONSPECTUS: Climate change, rising global energy demand, and energy security concerns motivate research into alternative, sustainable energy sources. In principle, solar energy can meet the world's energy needs, but the intermittent nature of solar illumination means that it is temporally and spatially separated from its consumption. Developing systems that promote solar-to-fuel conversion, such as via reduction of protons to hydrogen, could bridge this production−consumption gap, but this effort requires invention of catalysts that are cheap, robust, and efficient and that use earth-abundant elements. In this context, catalysts that utilize water as both an earthabundant, environmentally benign substrate and a solvent for proton reduction are highly desirable. This Account summarizes our studies of molecular metal−polypyridyl catalysts for electrochemical and photochemical reduction of protons to hydrogen. Inspired by concept transfer from biological and materials catalysts, these scaffolds are remarkably resistant to decomposition in water, with fast and selective electrocatalytic and photocatalytic conversions that are sustainable for several days. Their modular nature offers a broad range of opportunities for tuning reactivity by molecular design, including altering ancillary ligand electronics, denticity, and/or incorporating redox-active elements. Our first-generation complex, [(PY4)Co(CH 3 CN) 2 ] 2+, catalyzes the reduction of protons from a strong organic acid to hydrogen in 50% water. Subsequent investigations with the pentapyridyl ligand PY5Me 2 furnished molybdenum and cobalt complexes capable of catalyzing the reduction of water in fully aqueous electrolyte with 100% Faradaic efficiency. Of particular note, the complex [(PY5Me 2 )MoO] 2+ possesses extremely high activity and durability in neutral water, with turnover frequencies at least 8500 mol of H 2 per mole of catalyst per hour and turnover numbers over 600 000 mol of H 2 per mole of catalyst over 3 days at an overpotential of 1.0 V, without apparent loss in activity. Replacing the oxo moiety with a disulfide affords [(PY5Me 2 )MoS 2 ] 2+ , which bears a molecular MoS 2 triangle that structurally and functionally mimics bulk molybdenum disulfide, improving the catalytic activity for water reduction. In water buffered to pH 3, catalysis by [(PY5Me 2 )MoS 2 ] 2+ onsets at 400 mV of overpotential, whereas [(PY5Me 2 )MoO] 2+ requires an additional 300 mV of driving force to operate at the same current density. Metalation of the PY5Me 2 ligand with an appropriate Co(II) source also furnishes electrocatalysts that are active in water. Importantly, the onset of catalysis by the [(PY5Me 2 )Co(H 2 O)] 2+ series is anodically shifted by introducing electron-withdrawing functional groups on the ligand. With the [(bpy2PYMe)Co(CF 3 SO 3 )] 1+ system, we showed that introducing a redox-active moiety can facilitate the electro-and photochemical reduction of protons from weak acids such as acetic acid or water. Using a high-throughput photochemical reactor, we...

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Section: ■ Redox-active Ligands For Redox-leveling and Facilitating Mmentioning

confidence: 99%

Metal–Polypyridyl Catalysts for Electro- and Photochemical Reduction of Water to Hydrogen

et al. 2015

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“…Savéant and co-workers recently reported that in the presence 45 of strong acids, the boron-capped tris(glyoximato) cobalt clathrochelate complexes decompose to form cobalt-containing nanoparticles that are actually responsible for the observed H 2 generation activity. 50,51 In addition, considering the concerns on the homogeneous or heterogeneous nature of some water 50 oxidation cobalt catalysts published recently, 5254 we decided to investigate whether H 2 evolution detected during photolysis may come from colloidal nanoparticle or other heterogeneous cobalt species. To this end, dynamic light scattering (DLS) measurements were conducted for photolysis solutions after 0 h, 55 0.5 h, and 3 h of irradiation ( irr  455 nm) at room temperature.…”

Section: Photosensitizermentioning

confidence: 99%

Photocatalytic generation of hydrogen from water using a cobalt pentapyridine complex in combination with molecular and semiconductor nanowire photosensitizers

et al. 2013

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“…In this regard, some cobaloxime catalysts derived from dimethylglyoxime are active electrocatalytically and operate at particularly low overpotentials (9,18,19). One of these electrocatalysts, CoðdmgHÞ 2 ðpyrÞCl (dmgH ¼ dimethylglyoximate monoanion) has also been found to be active as a hydrogen generating catalyst when combined with a suitable photosensitizer and sacrificial electron donor (6,10,20).…”

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confidence: 99%

Cobalt-dithiolene complexes for the photocatalytic and electrocatalytic reduction of protons in aqueous solutions

McNamara

Han

Yin

et al. 2012

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

283

267

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Artificial photosynthesis (AP) is a promising method of converting solar energy into fuel (H 2 ). Harnessing solar energy to generate H 2 from H + is a crucial process in systems for artificial photosynthesis. Widespread application of a device for AP would rely on the use of platinum-free catalysts due to the scarcity of noble metals. Here we report a series of cobalt dithiolene complexes that are exceptionally active for the catalytic reduction of protons in aqueous solvent mixtures. All catalysts perform visible-light-driven reduction of protons from water when paired with as the photosensitizer and ascorbic acid as the sacrificial donor. Photocatalysts with electron withdrawing groups exhibit the highest activity with turnovers up to 9,000 with respect to catalyst. The same complexes are also active electrocatalysts in 1∶1 acetonitrile/water. The electrocatalytic mechanism is proposed to be ECEC, where the Co dithiolene catalysts undergo rapid protonation once they are reduced to . Subsequent reduction and reaction with H + lead to H 2 formation. Cobalt dithiolene complexes thus represent a new group of active catalysts for the reduction of protons.

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Efficient electrocatalytic hydrogen production from H+ ions using specially designed boron-capped cobalt clathrochelates

Abstract: Specially designed hexachlorine-containing cobalt(II) tris-dioximate clathrochelates were found to efficiently electrocatalyze the production of molecular hydrogen from H(+) ions without the overpotential of this process.

Cited by 86 publications

References 34 publications

Metal–Polypyridyl Catalysts for Electro- and Photochemical Reduction of Water to Hydrogen

Metal–Polypyridyl Catalysts for Electro- and Photochemical Reduction of Water to Hydrogen

Photocatalytic generation of hydrogen from water using a cobalt pentapyridine complex in combination with molecular and semiconductor nanowire photosensitizers

Cobalt-dithiolene complexes for the photocatalytic and electrocatalytic reduction of protons in aqueous solutions

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