| 1. |
- Bagnall, Andrew J., et al.
(författare)
-
Molecular Engineering of Electrocatalytic Nanomaterials for Hydrogen Evolution : The Impact of Structural and Electronic Modifications of Anchoring Linkers on Electrocatalysis
- 2024
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 14:8, s. 5630-5638
-
Tidskriftsartikel (refereegranskat)abstract
- The anticipated shortage of an increasing number of critical elements, especially metals, requires a shift toward molecularly defined materials with low metal loadings. More particularly, surface-anchored molecular catalysts are attractive to prospectively enable cost-effective electrochemical hydrogen evolution. However, the design of ligands integrating specific anchoring unit(s) for the immobilization of molecular catalysts can be challenging and has direct consequences for the intrinsic properties of the grafted complex. In this work, two cobalt tetraazamacrocyclic complexes bearing pyrene anchoring groups at different positions on the macrocyclic ligands were synthesized. The pyrene unit allows for simple immobilization and electrochemical characterization of the two complexes on multi-walled carbon nanotube-based electrodes. Thorough electrochemical and electrocatalytic investigation demonstrates important differences between the two closely related catalysts in terms of catalyst loading, catalytic response, and stability over time, with a significantly higher stability observed at pH 7 than at pH 2.
|
|
| 2. |
- Boniolo, Manuel
(författare)
-
Structural, Electronic and Reactive Properties of Pentapyridyl - Base Metal Complexes : Relevance for Water Oxidation Catalysis
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The rationalization of chemical-physical proprieties of transition metal complexes is fundamental in order to understand and tune their reactivity. In this thesis, a systematic investigation of the geometrical and electronic properties of [M(Py5OH)Cl]+ complexes (M= Mn, Fe, Co, Ni) has been performed, and their ability to act as molecular water oxidation catalysts has been probed. Through this scientific journey, new insights into their chemical and physical properties have been revealed. The spin crossover behavior of the ferrous chloride complex ([Fe(Py5OH)Cl]PF6) is the first example of a molecular Fe(II) complex coordinated to a weak-field ligand that can be thermodynamically stable in a low-spin electron configuration (Chapter 3). The spin state also dictates the electrochemical proprieties of the one-electron oxidized state of all the metal complexes investigated in our study (Chapter 4). The atypical rhombicity of the manganese complex ([Mn(Py5OH)Cl]PF6) gives an unusual anisotropic EPR signal for a Mn(II, S = 5/2) complex. This is compared with the analog [Mn(Py5OMe)Cl]PF6 complex providing, in combination with DFT calculations, insight into how the magnetic parameters (i.e., zero field splitting) are affected by small structural changes (Chapter 5). Finally, I investigated the role of water as substrate for water oxidation catalysis with the [M(Py5OH)Cl]+ complexes. The addition of small amounts of water into a non-aqueous medium allowed trapping possible water-bound intermediates for the Fe complex in the M(III) oxidation state but not for the other complexes. Nevertheless, all Py5OH-metal complexes are not particularly active catalysts with a maximum turnover number (TON) of 2. By introducing two methoxy functional groups, we obtained [Fe(Py5OMe)Cl]+ that turns out to facilitate water oxidation catalysis with a TON = 133 in a light-driven experiment. Further electrochemical experiments and post-catalytic solution analysis reveals that the oxygen evolution is generated by iron oxo/hydroxo species formed from the degradation of the methoxy-substituted Fe complex. This study highlights the difficulty of obtaining a stable base metal molecular catalyst and the importance of conducting a multi-technique analysis to attest firmly the nature of the catalysis (Chapter 6).
|
|
| 3. |
- Duan, Lele, et al.
(författare)
-
A molecular ruthenium catalyst with water-oxidation activity comparable to that of photosystem II
- 2012
-
Ingår i: Nature Chemistry. - 1755-4330 .- 1755-4349. ; 4:5, s. 418-423
-
Tidskriftsartikel (refereegranskat)abstract
- Across chemical disciplines, an interest in developing artificial water splitting to O-2 and H-2, driven by sunlight, has been motivated by the need for practical and environmentally friendly power generation without the consumption of fossil fuels. The central issue in light-driven water splitting is the efficiency of the water oxidation, which in the best-known catalysts falls short of the desired level by approximately two orders of magnitude. Here, we show that it is possible to close that 'two orders of magnitude' gap with a rationally designed molecular catalyst [Ru(bda)(isoq)(2)] (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; isoq = isoquinoline). This speeds up the water oxidation to an unprecedentedly high reaction rate with a turnover frequency of >300 s(-1). This value is, for the first time, moderately comparable with the reaction rate of 100-400 s(-1) of the oxygen-evolving complex of photosystem II in vivo.
|
|
| 4. |
|
|
| 5. |
- Dürr, Robin N., et al.
(författare)
-
Robust and Efficient Screen-Printed Molecular Anodes with Anchored Water Oxidation Catalysts
- 2021
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:10, s. 10534-10541
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we present the preparation and performance of screen-printed anodes for electrochemical water splitting in neutral media. With the combination of printed electrodes and molecular water oxidation catalysts, we successfully take advantage of a low-cost and up-scalable fabrication method of graphitic electrodes with the outstanding catalytic activity and stability of oligomeric ruthenium-based molecular water oxidation catalysts, offering a promising electroanode for water oxidation applications.
|
|
| 6. |
- Howe, Andrew, 1995-, et al.
(författare)
-
Carbanion Ruthenium Complexes for Water Oxidation
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A novel carbanion complex, [RuIII(dpa)(4,4’-bypridine)2], (dpa = ((5-methyl-1,3-phenylene)bis(pyridine-6,2-diyl))bis(hydroxy(l1-oxidaneyl)phosphine oxide),), has been prepared, characterised and incorporated as a coordination oligomer to form II@MWCNT@GC. Once incorporated in a coordination oligomer, this otherwise inert and stable diphosphonate complex has the ability to engage in electrocatalysis, with Faradaic efficiency (FE) of up to 85%. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy and XPS was used to confirm anchoring onto the graphitic surface.
|
|
| 7. |
- Howe, Andrew, et al.
(författare)
-
Electrocatalytic water oxidation from a mixed linker MOF based on NU-1000 with an integrated ruthenium-based metallo-linker
- 2022
-
Ingår i: Materials Advances. - : Royal Society of Chemistry (RSC). - 2633-5409. ; 3:10, s. 4227-4234
-
Tidskriftsartikel (refereegranskat)abstract
- A novel tetratopic metallo-linker, [Ru(tda)(py(PhCOOH)2)2], 1, (tda = 2,2′:6′,2′′-terpyridine-6,6′′-dicarboxylate; py(PhCOOH)2 = (4,4′-(pyridine-3,5-diyl)dibenzoic acid), that is structurally based on one of the most active molecular water oxidation catalysts has been prepared and fully characterized, including single crystal X-ray diffraction. 1 bears geometric similarities to H4TBAPy (H4TBAPy = 4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayl)tetrabenzoic acid), i.e. the native linker in NU-1000, which offers the possibility to synthesize NU-1000-Ru mixed linker MOFs solvothermally. Mixed linker MOF formation was demonstrated by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM), and Ru linker incorporation confirmed by FT-IR, energy-dispersive X-ray (EDX) spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES). It was found that the Ru contents in the final mixed linker MOFs correlate with the amount of Ru linker present during solvothermal synthesis, albeit not in a linear fashion. The cyclic voltammograms (CV) of the mixed linker MOFs are largely dominated by TBAPy-based oxidations with features attributed to 1. Interestingly, Ru linkers near the crystal surface are oxidized directly by interfacial hole transfer form the electrode, while those in the crystal interior can be oxidized indirectly from oxidized TBAPy linkers at more anodic potential. Upon repeated scanning, the CVs show the appearance of new waves that arise from irreversible TBAPy oxidation, as well as from the activation of the Ru-based water oxidation catalyst. Of the materials prepared, the one with the highest Ru content, NU-1000-Ruhigh, was shown to catalyze the electrochemical oxidation of water to dioxygen. The Faradaic efficiency (FE) of the construct is 37%, due to water oxidation being accompanied by oxidative transformations of the TBAPy linkers. Despite the low FE, NU-1000-Ruhigh is still among the best MOF-based water oxidation catalysts, operating by a unique co-linker mediated hole-transport mechanism to supply oxidizing equivalents also to catalysts in the crystal interior.
|
|
| 8. |
|
|
| 9. |
- Laine, Tanja M., 1979-
(författare)
-
Development of Ruthenium Catalysts for Water Oxidation
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An increasing global energy demand requires alternative fuel sources. A promising method is artificial photosynthesis. Although, the artificial processes are different from the natural photosynthetic process, the basic principles are the same, i.e. to split water and to convert solar energy into chemical energy. The energy is stored in bonds, which can at a later stage be released upon combustion. The bottleneck in the artificial systems is the water oxidation. The aim of this research has been to develop catalysts for water oxidation that are stable, yet efficient. The molecular catalysts are comprised of organic ligands that ultimately are responsible for the catalyst structure and activity. These ligands are often based on polypyridines or other nitrogen-containing aromatic compounds. This thesis describes the development of molecular ruthenium catalysts and the evaluation of their ability to mediate chemical and photochemical oxidation of water. Previous work from our group has shown that the introduction of negatively charged groups into the ligand frameworks lowers the redox potentials of the metal complexes. This is beneficial as it makes it possible to drive water oxidation with [Ru(bpy)3]3+-type oxidants (bpy = 2,2’-bipyridine), which can be photochemically generated from the corresponding [Ru(bpy)3]2+ complex. Hence, all the designed ligands herein contain negatively charged groups in the coordination site for ruthenium.The first part of this thesis describes the development of two mononuclear ruthenium complexes and the evaluation of these for water oxidation. Both complexes displayed low redox potentials, allowing for water oxidation to be driven either chemically or photochemically using the mild one-electron oxidant [Ru(bpy)3]3+.The second part is a structure–activity relationship study on several analogues of mononuclear ruthenium complexes. The complexes were active for water oxidation and the redox potentials of the analogues displayed a linear relationship with the Hammet σmeta parameter. It was also found that the complexes form high-valent Ru(VI) species, which are responsible for mediating O–O bond formation.The last part of the thesis describes the development of a dinuclear ruthenium complex and the catalytic performance for chemical and photochemical water oxidation. It was found that the complex undergoes O–O bond formation via a bridging peroxide intermediate, i.e. an I2M–type mechanism.
|
|
| 10. |
- Lee, Bao-Lin, 1976-
(författare)
-
Development of metal complexes for water oxidation
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In an artificial version of photosynthesis, sunlight and water are used to produce fuels. Our research focuses on the bottleneck in this process, the photooxidation of water. In the course of developing a water oxidation catalyst, a number of metal complexes have been synthesised, characterised, and studied for catalytic activity. Three of them are dinuclear complexes (Ru, Co and Cu) of 2,6-bis[(2-hydroxybenzyl)-(2-pyridylmethyl)aminomethyl]-4-methylphenol (H3bbpmp). The fourth is a dimeric Ru complex with a ligand containing imidazole and phenol motifs. Additionally, a dinuclear Mn complex with a ligand that contains benzimidazoles and carboxylates coordinating to the metal atoms was also developed. This Mn complex was then covalently linked to [Ru(bpy)3]2+-type photosensitisers, resulting in three different bimetallic dyads. Finally, a dinuclear Fe complex containing the same ligand as the dinuclear Mn complex was synthesised.The potential of the three H3bbpmp complexes as catalysts for oxidation of organic compounds was investigated and it was found that the Ru complex catalyses the oxidation of alcohols to the corresponding ketone or aldehyde using (diacetoxyiodo)benzene as oxidant. The Co complex functions as an electron transfer mediator in a coupled catalytic system for allylic oxidation using oxygen gas. The oxidation of 3,5-di-tert-butylcatechol to the corresponding ortho-quinone with oxygen gas using the copper complex proved that it can be considered as a model of catecholase. The dimeric Ru complex and the dinuclear Mn and Fe complexes proved to catalyse water oxidation when employing stoichiometric amounts of the oxidant [Ru(bpy)3](PF6)3. Furthermore, using [Ru(bpy)2(deeb)](PF6)2 as photosensitiser together with Na2S2O8 as sacrificial electron acceptor in aqueous phosphate buffer at pH = 7.2, photochemical water oxidation was demonstrated. The bimetallic dyads however, did not show catalytic activity for the oxidation of water.
|
|
