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Stepping into Catalysis: Kinetic and Mechanistic Investigations of Photo- and Electrocatalytic Hydrogen Production with Natural and Synthetic Molecular Catalysts
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. (Kemisk Fysik, Chemical Physics)
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In light of its rapidly growing energy demand, human society has an urgent need to become much more strongly reliant on renewable and sustainable energy carriers. Molecular hydrogen made from water with solar energy could provide an ideal case. The development of inexpensive, robust and rare element free catalysts is crucial for this technology to succeed. Enzymes in nature can give us ideas about what such catalysts could look like, but for the directed adjustment of any natural or synthetic catalyst to the requirements of large scale catalysis, its capabilities and limitations need to be understood on the level of individual reaction steps. This thesis deals with kinetic and mechanistic investigations of photo- and electrocatalytic hydrogen production with natural and synthetic molecular catalysts. Photochemical hydrogen production can be achieved with both E. coli Hyd-2 [NiFe] hydrogenase and a synthetic dinuclear [FeFe] hydrogenase active site model by ruthenium polypyridyl photosensitization. The overall quantum yields are on the order of several percent. Transient UV-Vis absorption experiments reveal that these yields are strongly controlled by the competition of charge recombination reactions with catalysis. With the hydrogenase major electron losses occur at the stage of enzyme reduction by the reduced photosensitizer. In contrast, catalyst reduction is very efficient in case of the synthetic dinuclear active site model. Here, losses presumably occur at the stage of reduced catalyst intermediates. Moreover, the synthetic catalyst is prone to structural changes induced by competing ligands such as secondary amines or DMF, which lead to catalytically active, potentially mononuclear, species. Investigations of electrocatalytic hydrogen production with a mononuclear catalyst by cyclic voltammetry provide detailed kinetic and mechanistic information on the catalyst itself. By extension of existing theory, it is possible to distinguish between alternative catalytic pathways and to extract rate constants for individual steps of catalysis. The equilibrium constant for catalyst protonation can be determined, and limits can be set on both the protonation and deprotonation rate constant. Hydrogen bond formation likely involves two catalyst molecules, and even the second order rate constant characterizing hydrogen bond formation and/or release can be determined.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 88 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1040
Keyword [en]
Artificial photosynthesis, photocatalysis, electrocatalysis, hydrogen production, proton reduction, hydrogenase, iron complex, active site model, catalytic mechanism, transient absorption, spectroscopy, electrochemistry, cyclic voltammetry
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Chemical Physics
Identifiers
URN: urn:nbn:se:uu:diva-197946ISBN: 978-91-554-8658-7 (print)OAI: oai:DiVA.org:uu-197946DiVA: diva2:615823
Public defence
2013-06-01, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:59 (English)
Opponent
Supervisors
Available from: 2013-05-08 Created: 2013-04-07 Last updated: 2013-08-30Bibliographically approved
List of papers
1. Light-Driven Hydrogen Production in Ruthenium Polypyridyl Photosensitized E. coli Hyd-2 [NiFe] Hydrogenase Studied by Steady-State and Time-Resolved UV-Vis Absorption Spectroscopy
Open this publication in new window or tab >>Light-Driven Hydrogen Production in Ruthenium Polypyridyl Photosensitized E. coli Hyd-2 [NiFe] Hydrogenase Studied by Steady-State and Time-Resolved UV-Vis Absorption Spectroscopy
(English)Manuscript (preprint) (Other academic)
National Category
Physical Chemistry Biophysics
Research subject
Physical Chemistry; Physical Biology
Identifiers
urn:nbn:se:uu:diva-198267 (URN)
Available from: 2013-04-11 Created: 2013-04-11 Last updated: 2013-04-29
2. High-Turnover Photochemical Hydrogen Production Catalyzed by a Model Complex of the [FeFe]-Hydrogenase Active Site
Open this publication in new window or tab >>High-Turnover Photochemical Hydrogen Production Catalyzed by a Model Complex of the [FeFe]-Hydrogenase Active Site
Show others...
2010 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, no 1, 60-63 p.Article in journal (Refereed) Published
Keyword
homogeneous catalysis, hydrogen, hydrogenase models, iron, photochemistry
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-137418 (URN)10.1002/chem.200902489 (DOI)000274007900005 ()
Available from: 2010-12-15 Created: 2010-12-15 Last updated: 2017-12-11
3. Comparing the Reactivity of Benzenedithiolate- versus Alkyldithiolate-Bridged Fe2(CO)6 Complexes with Competing Ligands
Open this publication in new window or tab >>Comparing the Reactivity of Benzenedithiolate- versus Alkyldithiolate-Bridged Fe2(CO)6 Complexes with Competing Ligands
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2011 (English)In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 7, 1106-1111 p.Article in journal (Refereed) Published
Abstract [en]

The reactivity of [(mu-X(2)bdt)Fe-2(CO)(6)] [(bdt)1, X(2)bdt = 3,6-di-substituted bezenedithiolate; X = H, Cl] with ligands of different donor strengths is investigated and compared to that of [(mu-pdt)Fe-2(CO)(6)] [(pdt) 1, pdt = propyldithiolate] and [(mu-edt)Fe-2(CO)(6)] [(edt)1, edt = ethyldithiolate]. Strong donor ligands (L = CN-, PMe3) when added to (bdt) 1 lead to mononuclear [(bdt)Fe(L)(2)(CO)(2)], (bdt)6(L), in a disproportionation and fragmentation reaction, while simple ligand-substitution reactions occur on (edt)1 and (pdt)1 under identical conditions. In the presence of weaker ligands such as secondary amines or dmf, the alkyldithiolate-bridged complexes are unreactive, while (bdt)1 transforms to an O-2-sensitive, magnetically uncoupled species, potentially a mononuclear Fe-I complex coordinated by bdt and at least 2 CO ligands.

Keyword
Enzyme models, Hydrogenases, IR spectroscopy, S ligands, Carbonyl ligands
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-150673 (URN)10.1002/ejic.201001152 (DOI)000288099000022 ()
Available from: 2011-04-04 Created: 2011-04-04 Last updated: 2017-12-11
4. Evaluating Molecular Catalysts for Multi-Electron Redox Processes - Kinetic and Mechanistic Information from Voltammetric Data
Open this publication in new window or tab >>Evaluating Molecular Catalysts for Multi-Electron Redox Processes - Kinetic and Mechanistic Information from Voltammetric Data
(English)Manuscript (preprint) (Other academic)
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-198266 (URN)
Available from: 2013-04-11 Created: 2013-04-11 Last updated: 2015-05-29

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