| 1. |
- Bagnall, Andrew J., et al.
(författare)
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Molecular Engineering of Electrocatalytic Nanomaterials for Hydrogen Evolution : The Impact of Structural and Electronic Modifications of Anchoring Linkers on Electrocatalysis
- 2024
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 14:8, s. 5630-5638
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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.
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| 2. |
- Boniolo, Manuel
(författare)
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Structural, Electronic and Reactive Properties of Pentapyridyl - Base Metal Complexes : Relevance for Water Oxidation Catalysis
- 2021
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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).
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| 3. |
- Dürr, Robin N., et al.
(författare)
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Robust and Efficient Screen-Printed Molecular Anodes with Anchored Water Oxidation Catalysts
- 2021
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:10, s. 10534-10541
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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.
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| 4. |
- Howe, Andrew, et al.
(författare)
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Electrocatalytic water oxidation from a mixed linker MOF based on NU-1000 with an integrated ruthenium-based metallo-linker
- 2022
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Ingår i: Materials Advances. - : Royal Society of Chemistry (RSC). - 2633-5409. ; 3:10, s. 4227-4234
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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.
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| 5. |
- Liseev, Timofey, et al.
(författare)
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Synthetic strategies to incorporate Ru-terpyridyl water oxidation catalysts into MOFs : direct synthesis vs. post-synthetic approach
- 2020
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Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 49:39, s. 13753-13759
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Tidskriftsartikel (refereegranskat)abstract
- Incorporating molecular catalysts into metal-organic frameworks (MOFs) is a promising strategy for improving their catalytic longevity and recyclability. In this article, we investigate and compare synthetic routes for the incorporation of the potent water oxidation catalyst Ru(tda)(pyCO(2)H)(2) (tda = 2,2':6',2 ''-terpyridine-6,6 ''-dicarboxylic acid, pyCO(2)H = iso-nicotinic acid) as a structural linker into a Zr-based UiO-type MOF. The task is challenging with this particular metallo-linker because of the equatorial dangling carboxylates that can potentially compete for Zr-coordination, as well as free rotation of the pyCO(2)H groups around the HO(2)Cpy center dot center dot center dot Ru center dot center dot center dot pyCO(2)H axis. As a consequence, all attempts to synthesize a MOF with the metallo-linker directly under solvothermal conditions led to amorphous materials with the Ru(tda) (pyCO(2)H)(2) linker coordinating to the Zr nodes in ill-defined ways, resulting in multiple waves in the cyclic voltammograms of the solvothermally obtained materials. On the other hand, an indirect post-synthetic approach in which the Ru(tda)(pyCO(2)H)(2) linker is introduced into a preformed edba-MOF (edba = ethyne dibenzoic acid) of UiO topology results in the formation of the desired material. Interestingly, two distinctly different morphologies of the parent edba-MOF have been discovered, and the impact that the morphological difference has on linker incorporation is investigated.
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