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Visible Light-Driven Water Oxidation by a Molecular Ruthenium Catalyst in Homogeneous System
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.ORCID iD: 0000-0003-1662-5817
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
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2010 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 49, no 1, 209-215 p.Article in journal (Refereed) Published
Abstract [en]

Discovery of an efficient catalyst bearing low overpotential toward water oxidation is a key step for light-driven water splitting into dioxygen and dihydrogen. A mononuclear ruthenium complex, Ru(II)L(pic)(2) (1) (H2L = 2,2'-bipyridine-6,6'-dicarboxylic acids pic = 4-picoline), was found capable of oxidizing water eletrochemically at a relatively low potential and promoting light-driven water oxidation using a three-component system composed of a photosensitizer, sacrificial electron acceptor, and complex 1. The detailed electrochemical properties of 1 were studied, and the onset potentials of the electrochemically catalytic curves in pH 7.0 and pH 1.0 solutions are 1.0 and 1.5 V, respectively. The low catalytic potential of 1 under neutral conditions allows the use of [Ru(bpy)(3)](2+) and even [Ru(dmbpy)(3)](2+) as a photosensitizer for photochemical water oxidation. Two different sacrificial electron acceptors, [Co(NH3)(5)Cl]Cl-2 and Na2S2O8, were used to generate the oxidized state of ruthenium tris(2,2'-bipyridyl) photosensitizers. In addition, a two-hour photolysis of I in a pH TO phosphate buffer did not lead to obvious degradation, indicating the good photostability of our catalyst. However, under conditions of light-driven water oxidation, the catalyst deactivates quickly. In both solution and the solid state under aerobic conditions, complex 1 gradually decomposed via oxidative degradation of its ligands, and two of the decomposed products, sp(3) C-H bond oxidized Ru complexes, were identified. The capability of oxidizing the sp(3) C-H bond implies the presence of a highly oxidizing Ru species, which might also cause the final degradation of the catalyst.

Place, publisher, year, edition, pages
2010. Vol. 49, no 1, 209-215 p.
Keyword [en]
O-O BOND, ARTIFICIAL PHOTOSYNTHESIS, FUNCTIONAL-MODEL, EXCITED-STATE, RU(II) COMPLEXES, REDOX PROPERTIES, PHOTOSYSTEM-II, O-2 EVOLUTION, OXYGEN, LIGAND
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-19065DOI: 10.1021/ic9017486ISI: 000272935800023Scopus ID: 2-s2.0-73349134347OAI: oai:DiVA.org:kth-19065DiVA: diva2:337112
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Artificial Water Splitting: Ruthenium Complexes for Water Oxidation
Open this publication in new window or tab >>Artificial Water Splitting: Ruthenium Complexes for Water Oxidation
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns the development and study of Ru-based water oxidation catalysts (WOCs) which are the essential components for solar energy conversion to fuels. The first chapter gives a general introduction about the field of homogenous water oxidation catalysis, including the catalytic mechanisms and the catalytic activities of some selected WOCs as well as the concerns of catalyst design. The second chapter describes a family of mononuclear Ru complexes [Ru(pdc)L3] (H2pdc = 2,6-pyridinedicarboxylic acid; L = pyridyl ligands) towards water oxidation. The negatively charged pdc2 dramatically lowers the oxidation potentials of Ru complexes, accelerates the ligand exchange process and enhances the catalytic activity towards water oxidation. A Ru aqua species [Ru(pdc)L2(OH2)] was proposed as the real catalyst. The third chapter describes the analogues of [Ru(terpy)L3]2+ (terpy = 2,2′:6′,2′′-terpyridine). Through the structural tailor, the ligand effect on the electrochemical and catalytic properties of these Ru complexes was studied. Mechanistic studies suggested that these Ru-N6 complexes were pre-catalysts and the Ru-aqua species were the real WOCs. The forth chapter describes a family of fast WOCs [Ru(bda)L2] (H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid). Catalytic mechanisms were thoroughly investigated by electrochemical, kinetic and theoretical studies. The main contributions of this work to the field of water oxidation are (i) the recorded high reaction rate of 469 s−1; (ii) the involvement of seven-coordinate Ru species in the catalytic cycles; (iii) the O-O bond formation pathway via direct coupling of two Ru=O units and (iv) non-covalent effects boosting up the reaction rate. The fifth chapter is about visible light-driven water oxidation using a three component system including a WOC, a photosensitizer and a sacrificial electron acceptor. Light-driven water oxidation was successfully demonstrated using our Ru-based catalysts.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 80 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:48
Keyword
water oxidation, ruthenium, electrochemistry, DFT calculation, photoelectrochemistry, negatively charged ligand, catalyst
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-40848 (URN)978-91-7501-083-0 (ISBN)
Public defence
2011-10-07, E3, Osquars backe 14, KTH, Stockholm, 10:00 (English)
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Note
QC 20110922Available from: 2011-09-22 Created: 2011-09-21 Last updated: 2011-09-22Bibliographically approved

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