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SnIVMetalloporphyrin/CoIII Complex: An All-Abundant-Element System for the Photocatalytic Production of H2 in Aqueous Solution


Mintrop, Luise; Windisch, Johannes; Gotzmann, Carla; Alberto, Roger; Probst, Benjamin; Kurz, Philipp (2015). SnIVMetalloporphyrin/CoIII Complex: An All-Abundant-Element System for the Photocatalytic Production of H2 in Aqueous Solution. Journal of Physical Chemistry B, 119(43):13698-13706.

Abstract

A new, molecular system for the light-driven production of hydrogen in aqueous solution was developed by combining a water-soluble tin porphyrin ([SnIVCl2TPPC], A) acting as photosensitizer with a cobalt-based proton-reduction catalyst ([CoIIICl(dmgH)2(py)], C). Under visible light illumination and with triethanolamine (TEOA) as electron source, the system evolves H2 for hours and is clearly catalytic in both dye and catalyst. A detailed analysis of the relevant redox potentials in combination with time-resolved spectroscopy resulted in the development of a Z-scheme type model for the flow of electrons in this system. Key intermediates of the proposed mechanism for the pathway leading to H2 are the porphyrin dye’s highly oxidizing singlet excited state 1A* (E ∼ +1.3 V vs NHE), its strongly reducing isobacteriochlorin analogue (E ∼ +0.95 V), and the CoI form of C (E ∼ −0.8 V), acting as catalyst for H2 formation. Among other results, the suggested reaction sequence is supported by the detection of a shortened excited-state lifetime for singlet 1A* (τ ∼ 1.75 ns) in the presence of TEOA and the ultraviolet–visible detection of the SnIV isobacteriochlorin intermediate at λ = 610 nm. Thus, a molecular, conceptually biomimetic, and precious-metal-free reaction chain was found which photocatalytically generates H2 in a 100% aqueous system from an electron donor with a high oxidation potential (E(TEOA) ∼ +1.1 V). On the other hand, at identical conditions, this photoreaction chain yields H2 markedly slower than a system using the photosensitizer [ReI(CO)3(bpy) (py)]+, probably due to the much longer excited-state lifetime (τ ∼ 120 ns) of the rhenium dye and better electron-transfer rates caused by its simple single-electron photoreduction chemistry.

Abstract

A new, molecular system for the light-driven production of hydrogen in aqueous solution was developed by combining a water-soluble tin porphyrin ([SnIVCl2TPPC], A) acting as photosensitizer with a cobalt-based proton-reduction catalyst ([CoIIICl(dmgH)2(py)], C). Under visible light illumination and with triethanolamine (TEOA) as electron source, the system evolves H2 for hours and is clearly catalytic in both dye and catalyst. A detailed analysis of the relevant redox potentials in combination with time-resolved spectroscopy resulted in the development of a Z-scheme type model for the flow of electrons in this system. Key intermediates of the proposed mechanism for the pathway leading to H2 are the porphyrin dye’s highly oxidizing singlet excited state 1A* (E ∼ +1.3 V vs NHE), its strongly reducing isobacteriochlorin analogue (E ∼ +0.95 V), and the CoI form of C (E ∼ −0.8 V), acting as catalyst for H2 formation. Among other results, the suggested reaction sequence is supported by the detection of a shortened excited-state lifetime for singlet 1A* (τ ∼ 1.75 ns) in the presence of TEOA and the ultraviolet–visible detection of the SnIV isobacteriochlorin intermediate at λ = 610 nm. Thus, a molecular, conceptually biomimetic, and precious-metal-free reaction chain was found which photocatalytically generates H2 in a 100% aqueous system from an electron donor with a high oxidation potential (E(TEOA) ∼ +1.1 V). On the other hand, at identical conditions, this photoreaction chain yields H2 markedly slower than a system using the photosensitizer [ReI(CO)3(bpy) (py)]+, probably due to the much longer excited-state lifetime (τ ∼ 120 ns) of the rhenium dye and better electron-transfer rates caused by its simple single-electron photoreduction chemistry.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:29 October 2015
Deposited On:13 Jan 2016 15:52
Last Modified:14 Feb 2018 10:29
Publisher:American Chemical Society (ACS)
ISSN:1520-5207
OA Status:Closed
Publisher DOI:https://doi.org/10.1021/acs.jpcb.5b03106

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