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Ru-Based Water Oxidation Catalysts: Development and Mechanistic Studies
Stockholm University, Faculty of Science, Department of Organic Chemistry. (Group of Prof. Björn Åkermark)ORCID iD: 0000-0002-7249-7437
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oxidation of water constitutes one of the most challenging processes in artificial photosynthesis, which aims at storing solar energy in the form of chemical bonds of high-energy fuels. To facilitate this process, efficient and durable water oxidation catalysts have to be developed and integrated into the complete photosynthetic cells. Importantly, the intricate complexity of such devices requires the catalyst not only to be highly efficient and robust, but also operate through a well-defined mechanism.

This thesis describes the development and mechanistic studies of new water oxidation catalysts based on ruthenium. The first part of the thesis describes the synthesis of a dinuclear ruthenium-based catalyst active for both chemical and light-driven water oxidation. This catalyst displayed a pronounced influence of the acetonitrile co-solvent on the redox properties, which was studied in detail by electrochemical methods. In the second part, a new benzimidazole-based mononuclear catalyst was evaluated. The activity of the catalyst was studied for chemical and light-driven water oxidation, and insight into the operating mechanism was provided with the help of density functional theory calculations. In the third part of the thesis, a new mononuclear ruthenium-based catalyst was prepared and evaluated for electrochemically-driven water oxidation. This catalyst displayed activity similar to that of the current state-of-the-art water oxidation catalyst, while eliminating its main drawback, that is incomplete activation. The redox properties of the new catalyst were studied in detail by electrochemical and spectroscopic techniques, providing insight into the origins of its improved performance. Finally, in the fourth part of the thesis, a heterogeneous nanoparticulate catalyst immobilized on a solid support is described. The catalyst displayed high activity and stability during chemical and light-driven water oxidation, which was attributed to the small average particle size and efficient anchoring of the catalyst to the heterogeneous support via an oxidatively-stable linker.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University , 2018. , p. 73
Keywords [en]
ruthenium, catalysis, water oxidation, artificial photosynthesis
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-160718ISBN: 978-91-7797-466-6 (print)ISBN: 978-91-7797-467-3 (electronic)OAI: oai:DiVA.org:su-160718DiVA, id: diva2:1257081
Public defence
2018-12-05, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2018-11-12 Created: 2018-10-18 Last updated: 2018-11-02Bibliographically approved
List of papers
1. Catalyst-solvent interactions in a dinuclear Ru-based water oxidation catalyst
Open this publication in new window or tab >>Catalyst-solvent interactions in a dinuclear Ru-based water oxidation catalyst
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2016 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 45, no 47, p. 19024-19033Article in journal (Refereed) Published
Abstract [en]

Photocatalytic water oxidation represents a key process in conversion of solar energy into fuels and can be facilitated by the use of molecular transition metal-based catalysts. A novel straightforward approach for covalent linking of the catalytic units to other moieties is demonstrated by preparation of a dinuclear complex containing two [Ru(pdc)(pic)(3)]-derived units (pdc = 2,6-pyridinedicarboxylate, pic = 4-picoline). The activity of this complex towards chemical and photochemical oxidation of water was evaluated and a detailed insight is given into the interactions between the catalyst and acetonitrile, a common co-solvent employed to increase solubility of water oxidation catalysts. The solvent-induced transformations were studied by electrochemical and spectroscopic techniques and the relevant quantitative parameters were extracted.

National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-139388 (URN)10.1039/c6dt03789e (DOI)000390082900029 ()27853776 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationCarl Tryggers foundation
Available from: 2017-02-07 Created: 2017-02-06 Last updated: 2019-07-17Bibliographically approved
2. Chemical and Photochemical Water Oxidation Mediated by an Efficient Single-Site Ruthenium Catalyst
Open this publication in new window or tab >>Chemical and Photochemical Water Oxidation Mediated by an Efficient Single-Site Ruthenium Catalyst
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2016 (English)In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 9, no 24, p. 3448-3456Article in journal (Refereed) Published
Abstract [en]

Water oxidation is a fundamental step in artificial photosynthesis for solar fuels production. In this study, we report a single-site Ru-based water oxidation catalyst, housing a dicarboxylate-benzimidazole ligand, that mediates both chemical and light-driven oxidation of water efficiently under neutral conditions. The importance of the incorporation of the negatively charged ligand framework is manifested in the low redox potentials of the developed complex, which allows water oxidation to be driven by the mild one-electron oxidant [Ru(bpy)(3)](3+) (bpy = 2,2'-bipyridine). Furthermore, combined experimental and DFT studies provide insight into the mechanistic details of the catalytic cycle.

Keywords
electrochemistry, homogeneous catalysis, photochemistry, ruthenium, water oxidation
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-141313 (URN)10.1002/cssc.201601171 (DOI)000394571500013 ()27966290 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationCarl Tryggers foundation
Available from: 2017-04-03 Created: 2017-04-03 Last updated: 2018-10-19Bibliographically approved
3. Highly Active Ruthenium-Based Water Oxidation Catalyst with an Easy Access to the Catalytically Active Species
Open this publication in new window or tab >>Highly Active Ruthenium-Based Water Oxidation Catalyst with an Easy Access to the Catalytically Active Species
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Herein is described a highly active ruthenium-based water oxidation catalyst [RuIV(mcbp)(O)(py)2] (5, mcbp2− = 2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine), which can be generated from either [RuII(mcbp)(py)2] (4II) or [RuIII(Hmcbp)(py)2]2+ (4III). Complexes 4II and 4III were isolated and characterized by single crystal X-ray analysis, NMR, UV-vis, FT-IR, ESI-HRMS, EPR, and elemental analysis, and their redox properties were studied in detail by electrochemical and spectroscopic methods. Unlike for the parent catalyst [Ru(tda)(py)2] (1, tda2− = [2,2′:6′,2″-terpyridine]-6,6″-dicarboxylate), for which full transformation to the catalytically active species [RuIV(tda)(O)(py)2] (2) could not be carried out — stoichiometric generation of the catalytically active Ru-aqua complex 5 from 4II was achieved under mild conditions (pH 7.0) and short reaction times. The redox properties of the catalyst were studied and its activity for electrocatalytic water oxidation was evaluated, reaching TOFmax ≈ 40 000 s−1 at pH 9.0 (from the foot-of-the-wave analysis, FOWA), which is comparable to the activity of the state-of-the-art catalyst 2.

Keywords
artificial photosynthesis, water oxidation catalyst, oxygen evolution, ruthenium, molecular catalysis
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-161300 (URN)
Available from: 2018-10-19 Created: 2018-10-19 Last updated: 2018-10-22Bibliographically approved
4. Water oxidation mediated by ruthenium oxide nanoparticles supported on siliceous mesocellular foam
Open this publication in new window or tab >>Water oxidation mediated by ruthenium oxide nanoparticles supported on siliceous mesocellular foam
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2017 (English)In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 7, no 1, p. 293-299Article in journal (Refereed) Published
Abstract [en]

Artificial photosynthesis is an attractive strategy for converting solar energy into fuel. In this context, development of catalysts for oxidation of water to molecular oxygen remains a critical bottleneck. Herein, we describe the preparation of a well-defined nanostructured RuO2 catalyst, which is able to carry out the oxidation of water both chemically and photochemically. The developed heterogeneous RuO2 nanocatalyst was found to be highly active, exceeding the performance of most known heterogeneous water oxidation catalysts when driven by chemical or photogenerated oxidants.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-140390 (URN)10.1039/c6cy02121b (DOI)000392399900027 ()
Funder
Swedish Research CouncilBerzelii Centre EXSELENTEU, European Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2017-03-20 Created: 2017-03-20 Last updated: 2019-02-15Bibliographically approved

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