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Artificial Photosynthesis: Molecular Catalysts for Water Oxidation
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. (Licheng Sun)
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Artificial photosynthesis provides a promising solution to the future sustainable energy system. Water is the only suitably sufficient protons and electrons supplier by the reaction of water oxidation. However, this reaction is both kinetically and thermodynamically demanding, leading to a sluggish kinetics unless the introduction of a catalyst.The theme of this thesis is to design, synthesize and evaluate molecular catalysts for water oxidation. This thesis consists of seven parts:The first chapter presents a general introduction to the field of homogenous catalysis of water oxidation, including catalysts design, examination and mechanistic investigation.The second chapter investigates the electronic and noncovalent-interaction effects of the ligands on the activities of the catalysts.In the third chapter, halogen substitutes are introduced into the axial ligands of the ruthenium catalysts. It is proved that the hydrophobic effect of the halogen atom dramatically enhanced the reactivity of the catalysts.Chapter four explores a novel group of ruthenium catalysts with imidazole-DMSO pair of axial ligands, in which the DMSO is proved to be crucial for the high efficiency of the catalysts.Chapter five describes the light-driven water oxidation including the three-component system and the sensitizer-catalyst assembled system. It is found that the common Ru(bpy)32+ dye can act as an electron relay and further benefit the electron transfer as well as the photo-stability of the system.In chapter six, aiming to the future application, selected ruthenium catalysts have been successfully immobilized on electrodes surfaces, and the electrochemical water oxidation is achieved with high efficiency.Finally, in the last chapter, a novel molecular catalyst based on the earth abundant metal ―nickel has been designed and synthesized. The activities as well as the mechanism have been explored.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , 82 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:40
Keyword [en]
artificial photosynthesis, water oxidation, ruthenium complexes, nickel complexes, cerium, photo-catalysts, photosensitizer, electrochemistry, immobilization.
National Category
Organic Chemistry Physical Chemistry
Research subject
Chemistry; Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-173622ISBN: 978-91-7595-659-6 (print)OAI: oai:DiVA.org:kth-173622DiVA: diva2:854364
Public defence
2015-10-13, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency
Note

QC 20150916

Available from: 2015-09-16 Created: 2015-09-15 Last updated: 2015-09-16Bibliographically approved
List of papers
1. Insights into Ru-Based Molecular Water Oxidation Catalysts: Electronic and Noncovalent-Interaction Effects on Their Catalytic Activities
Open this publication in new window or tab >>Insights into Ru-Based Molecular Water Oxidation Catalysts: Electronic and Noncovalent-Interaction Effects on Their Catalytic Activities
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2013 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 52, no 14, 7844-7852 p.Article in journal (Refereed) Published
Abstract [en]

A series of Ru-bda water oxidation catalysts [Ru(bda)L-2] (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; L = [HNEt3][3-SO3-pyridine], 1; 4-(EtOOC)-pyridine, 2; 4-bromopyridine, 3; pyridine, 4; 4-methoxypyridine, 5; 4-(Me2N)-pyridine, 6; 4-[Ph(CH2)(3)]-pyridine, 7) were synthesized with election-donating/-withdrawing groups and hydro-philic/hydrophobic groups in the axial ligands. These complexes were characterized by H-1 NMR spectroscopy, high-resolution mass spectrometry, elemental analysis, and electrochemistry. In addition, complexes 1 and 6 were further identified by single crystal X-ray crystallography, revealing a highly distorted octahedral configuration of the Ru coordination sphere. All of these complexes are highly active toward Ce-IV-driven (Ce-IV = Ce(NH4)(2)(NO3)(6)) water oxidation with oxygen evolution rates up to 119 mols of O-2 per mole of catalyst per second. Their structure-activity relationship was investigated. Electron-withdrawing and noncovalent interactions (attraction) exhibit positive effect on the catalytic activity of Ru-bda catalysts.

Keyword
Mononuclear Ruthenium Complexes; O-O Bond; Iridium Complexes; Redox Properties; Functional-Model; Photosystem-Ii; O-2 Evolution; Efficient; Ligands; Site
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-129127 (URN)10.1021/ic302687d (DOI)000322087100007 ()2-s2.0-84880260882 (Scopus ID)
Note

QC 20130920

Available from: 2013-09-20 Created: 2013-09-19 Last updated: 2017-12-06Bibliographically approved
2. Highly efficient and robust molecular water oxidation catalysts based on ruthenium complexes
Open this publication in new window or tab >>Highly efficient and robust molecular water oxidation catalysts based on ruthenium complexes
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2014 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 50, no 85, 12947-12950 p.Article in journal (Refereed) Published
Abstract [en]

Two monomeric ruthenium molecular catalysts for water oxidation have been prepared, and both of them show high activities in pH 1.0 aqueous solutions, with an initial rate of over 1000 turnover s(-1) by complex 1, and a turnover number of more than 100 000 by complex 2.

National Category
Organic Chemistry Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-155503 (URN)10.1039/c4cc05069j (DOI)000342756100036 ()2-s2.0-84907611162 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20141110

Available from: 2014-11-10 Created: 2014-11-06 Last updated: 2017-12-05Bibliographically approved
3. Toward Controlling Water Oxidation Catalysis: Tunable Activity of Ruthenium Complexes with Axial Imidazole/DMSO Ligands
Open this publication in new window or tab >>Toward Controlling Water Oxidation Catalysis: Tunable Activity of Ruthenium Complexes with Axial Imidazole/DMSO Ligands
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2012 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 45, 18868-18880 p.Article in journal (Refereed) Published
Abstract [en]

Using the combinations of imidazole and dimethyl :sulfoxide (DMSO) as axial ligands and 2,2'-bipyridine-6,6'-dicarboxylate (bda) as the equatorial ligand, we have synthesized six novel ruthenium complexes with noticeably different activity as water oxidation catalysts (WOCs). In four C-s symmetric Ru-II(kappa(3)-bda)(DMSO)L-2 complexes L = imidazole (1), N-methylimidazole (2), 5-methylimidazole (3), and 5-bromo-N-methylimidazole (4). Additionally, in two C-2v symmetric Ru-II(kappa(4)-bda)L-2 complexes L = 5-nitroimidazole (5) and 5-bromo-N-methylimidazole (6), that is, fully equivalent axial imidazoles. A detailed characterization of all complexes and the mechanistic investigation of the catalytic water oxidation have been carried out with a number of experimental techniques, that is, kinetics, electrochemistry and high resolution mass spectrometry (HR-MS), and density functional theory (DFT) calculations. We have observed the in situ formation: of a Ru-II-complex with the accessible seventh coordination position. The measured catalytic activities and kinetics of complex 1-6 revealed details about an important structure activity relation: the connection between the nature of axial ligands in the combination and either the increase or decrease of the catalytic activity. In particular, an axial DMSO group substantially increases the turnover frequency of WOCs reported in article, with the ruthenium-complex having one axial 5-bromo-N-methylimidazole and one axial DMSO: (4), we have obtained a high initial turnover frequency of similar to 180 s(-1). DFT modeling Of the binuclear reaction pathway of the O-O bond formation in catalytic Water oxidation further corroborated the concept of the mechanistic significance of the axial ligands and rationalized the experimentally observed difference in the activity of complexes with imidazole/DMSO and imidazole/imidazole combinations of axial ligands.

Keyword
O-O Bond, Redox Properties, Photosystem-Ii, Molecular Catalysts, Iridium Complexes, Dimer Complex, Mechanisms, Photosynthesis, Intermediate, Family
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-109191 (URN)10.1021/ja309805m (DOI)000311192100060 ()2-s2.0-84869478208 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20130107

Available from: 2013-01-07 Created: 2012-12-21 Last updated: 2017-12-06Bibliographically approved
4. Visible light-driven water oxidation catalyzed by mononuclear ruthenium complexes
Open this publication in new window or tab >>Visible light-driven water oxidation catalyzed by mononuclear ruthenium complexes
2013 (English)In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 306, 129-132 p.Article in journal (Refereed) Published
Abstract [en]

A series of mononuclear ruthenium water oxidation catalysts (WOCs) [Ru(bda)L-2] (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; L = N-cyclic aromatic ligands) were investigated in three-component light-driven water oxidation systems composed of photosensitizers, a sacrificial electron acceptor, and WOCs. A high turnover number of 579 for water oxidation was achieved in the homogeneous system using complex 4 ([Ru(bda)(4-Br-pyridine)(2)]) as the WOC, and a high quantum efficiency of 17% was found which is a new record for visible light-driven water oxidation in homogeneous systems.

Keyword
Photochemistry, Homogeneous catalysis, Water oxidation, Ruthenium, Quantum yield
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-129437 (URN)10.1016/j.jcat.2013.06.023 (DOI)000323865500013 ()2-s2.0-84881158429 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20131002

Available from: 2013-10-02 Created: 2013-09-30 Last updated: 2017-12-06Bibliographically approved
5. Sensitizer-Catalyst Assemblies for Water Oxidation
Open this publication in new window or tab >>Sensitizer-Catalyst Assemblies for Water Oxidation
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2015 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 54, no 6, 2742-2751 p.Article in journal (Refereed) Published
Abstract [en]

Two molecular assemblies with one Ru(II)-polypyridine photosensitizer covalently linked to one Ru(II)(bda)L2 catalyst (1) (bda = 2,2'-bipyridine-6,6'-dicarboxylate) and two photosensitizers covalently linked to one catalyst (2) have been prepared using a simple C-C bond as the linkage. In the presence of sodium persulfate as a sacrificial electron acceptor, both of them show high activity for catalytic water oxidation driven by visible light, with a turnover number up to 200 for 2. The linked photocatalysts show a lower initial yield for light driven oxygen evolution but a much better photostability compared to the three component system with separate sensitizer, catalyst and acceptor, leading to a much greater turnover number. Photocatalytic experiments and time-resolved spectroscopy were carried out to probe the mechanism of this catalysis. The linked catalyst in its Ru(II) state rapidly quenches the sensitizer, predominantly by energy transfer. However, a higher stability under photocatalytic condition is shown for the linked sensitizer compared to the three component system, which is attributed to kinetic stabilization by rapid photosensitizer regeneration. Strategies for employment of the sensitizer-catalyst molecules in more efficient photocatalytic systems are discussed.

National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-164446 (URN)10.1021/ic502915r (DOI)000351325200028 ()25700086 (PubMedID)2-s2.0-84925014467 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20150423

Available from: 2015-04-23 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
6. Electrochemical driven water oxidation by molecular catalysts in situ polymerized on the surface of graphite carbon electrode
Open this publication in new window or tab >>Electrochemical driven water oxidation by molecular catalysts in situ polymerized on the surface of graphite carbon electrode
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2015 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 51, no 37, 7883-7886 p.Article in journal (Refereed) Published
Abstract [en]

A simple strategy to immobilize highly efficient ruthenium based molecular water-oxidation catalysts on the basal-plane pyrolytic graphite electrode (BPG) by polymerization has been demonstrated. The electrode 1@BPG has obtained a high initial turnover frequency (TOF) of 10.47 s-1 at ∼700 mV overpotential, and a high turnover number (TON) up to 31600 in 1 h electrolysis.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-167712 (URN)10.1039/c5cc00242g (DOI)000353639300026 ()2-s2.0-84928537759 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20150602

Available from: 2015-06-02 Created: 2015-05-22 Last updated: 2017-12-04Bibliographically approved
7. Towards Water Splitting Device: Functionalizing Electrodes with Ru catalyst by in situPolymerization
Open this publication in new window or tab >>Towards Water Splitting Device: Functionalizing Electrodes with Ru catalyst by in situPolymerization
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-173669 (URN)
Note

QS 2015

Available from: 2015-09-16 Created: 2015-09-16 Last updated: 2015-09-16Bibliographically approved
8. A Nickel (II) PY5 Complex as an Electrocatalyst for Water Oxidation
Open this publication in new window or tab >>A Nickel (II) PY5 Complex as an Electrocatalyst for Water Oxidation
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2016 (English)In: Journal of Catalysis, ISSN 0021-9517, Vol. 335, 72-78 p.Article in journal (Refereed) Published
Abstract [en]

A Ni-PY5 [PY5 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine)] complex has been found to act as an electrocatalyst for oxidizing water to dioxygen in aqueous phosphate buffer solutions. The rate of water oxidation catalyzed by the Ni-PY5 is remarkably enhanced by the proton acceptor base HPO42−, with rate constant of 1820 M−1 s−1. Controlled potential bulk electrolysis with Ni-PY5 at pH 10.8 under an applied potential of 1.5 V vs. normal hydrogen electrode (NHE) resulted in dioxygen formation with a high faradaic efficiency over 90%. A detailed mechanistic study identifies the water nucleophilic attack pathway for water oxidation catalysis.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Nickel complex, Water oxidation catalyst, Electrochemistry, Water nucleophilic attack
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-173670 (URN)10.1016/j.jcat.2015.12.003 (DOI)000371098200007 ()2-s2.0-84954413362 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20160208

Available from: 2015-09-16 Created: 2015-09-16 Last updated: 2017-01-25Bibliographically approved

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