| 1. |
- Colozza, Noemi, et al.
(författare)
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Insights into Tripodal Tris(pyrazolyl) Compounds as Ionophores for Potentiometric Ammonium Ion Sensing
- 2022
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Ingår i: ChemElectroChem. - : Wiley. - 2196-0216. ; 9:18
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Tidskriftsartikel (refereegranskat)abstract
- The decentralisation of accurate determination of the ammonium ion (NH4+) is relevant for environmental monitoring (i. e., nitrogen cycle) and certain clinical applications (e. g., kidney and liver diseases). Potentiometric ionophore-based sensors are one alternative for these purposes in terms of versatile implementation, though the potassium ion (K+) is known to be a major source of interference. We herein investigate the use of three different tripodal tris(pyrazolyl) compounds derived from 1,3,5-triethylbenzene as NH4+ ionophores. A complete set of potentiometric experiments together with theoretical simulations reveals suitable analytical performance while demonstrating a suppression of the K+ interference given the formation of an adequate cavity in the ionophore to host NH4+ over K+ in the membrane environment. The results support the use of these electrodes in the analytical detection of NH4+ in a wide range of samples with variable contents.
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| 2. |
- de Gracia Triviño, Juan Angel, 1989-, et al.
(författare)
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Removing the Barrier in O-O Bond Formation Via the Combination of Intramolecular Radical Coupling and the Oxide Relay Mechanism
- 2024
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 128:19, s. 3794-3800
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Tidskriftsartikel (refereegranskat)abstract
- The Ru(tda) catalyst has been a major milestone in the development of molecular water oxidation catalysts due to its outstanding performance at neutral pH. The role of the noncoordinating carboxylate group is to act as a nucleophile, donating an oxygen atom to the oxo group, thereby acting as an oxide relay (OR) mechanism for O-O bond formation. A substitution of the carboxylates for phosphonate groups has been proposed, resulting in the Ru(tPaO) catalyst, which has shown even more efficient performance in experimental characterization. In this study, we explore the feasibility of the OR mechanism in the newly reported Ru(tPaO) molecular catalyst. We investigated the catalytic cycle using density functional theory and identified a variation of the OR mechanism that involves radical oxygen atoms in O-O bond formation. We have also determined that the subsequent hydroxide nucleophilic attack is the sole rate-limiting step in the catalytic cycle. All activation free energies are very low, with a free-energy barrier of 2.1 kcal/mol for O-O bond formation and 4.2 kcal/mol for OH- nucleophilic attack.
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| 3. |
- Juan Angel, de Gracia Triviño, 1989-, et al.
(författare)
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Combining intramolecular radical coupling with the Oxide Relay mechanism: Radical Oxide Relay mechanism
- 2022
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Annan publikation (populärvet., debatt m.m.)abstract
- The Ru(tda) catalyst has been a major milestone in the development of molecular water oxidation catalysts due to its outstanding performance at neutral pH. The role of the non-coordinating carboxylate group is to act as a nucleophile, donating an oxygen atom to the oxo group, acting as an oxide relay mechanism the the O-O bond formation. A substitution of the carboxylates for phosphonate groups has been proposed, the Ru(tPaO), and its experimental characterization has shown an even more efficient performance. In this study, we explore the feasibility of the oxide relay mechanism in the newly reported Ru(tPaO) molecular catalyst. We have explored the catalytic cycle using density functional theory and we have identified a variation of the oxide relay mechanism that involves radical oxygen atoms in the O-O bond formation. We have explored the origin of the radical character in this complex and we have identified the hydroxyl nucleophilic attack as the sole rate limiting step in the catalytic cycle. The barriers are very low in all the steps, the O-O bond formation has a free energy barrier of 2.1 kcal/mol and the OH- nucleophilic attack 4.2 kcal/mol.
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| 4. |
- Juan Angel, de Gracia Triviño, 1989-
(författare)
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From Molecular Catalysts to Hybrid Electrodes: A Theoretical Guide
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The industrial revolution thrived our society to great technological advancement and a shift from an agrarian to an industrial society. Besides this fact, the side effect has been the development of a society highly dependent on energy, and the main sources of energy are based on non-renewable fossil fuels. This issue calls for the quest for new renewable energy sources that can address the energy dependency minimizing its side effects of it. In this quest, hydrogen is a promising source due to its high energy capacity and clean sub-products.The first chapter of this thesis will revise more in deep this environmental issues and what is needed to implement sustainable hydrogen production by water splitting. As well, as how the water source is extremely relevant, and solutions for using seawater are required to scale up hydrogen production. Also, an introduction to molecular catalysts for water oxidation based on Ru will be exposed, including a historical perspective and the state of the art at this day. The first chapter will finish with the strategies explored in this thesis to overcome the limitations of molecular catalysts in water splitting devices i.e, stability and current density.This work uses an ample set of computational tools to explore the reactivity and supramolecular properties of molecular catalysts. The second chapter will start with the treatment of molecules as electronic systems utilizing molecular quantum mechanics. Wave function formalism and density functional formalism of molecular quantum mechanics will be exposed and explained to the extent that is needed to ground the results of this thesis. The next section will introduce the treatment of molecules as atomic systems employing molecular mechanics and how we derive relevant supramolecular effects such as hydrophobicity, means of attachment to electrode surfaces, solvent, and electric field effects. Finally, this chapter will revise the Empirical Valence Bond approach to study the reactivity dependence on the molecular environment.The last chapter will go over the results of this thesis that correspond to the annexed papers at the end of this work. Starting from the characterization of the oxide relay mechanism in the highly efficient catalyst Ru(tda) where a novel function for the non-coordinating carboxylate ligand is proposed. To increase the stability of the Ru(tda) an attachment to carbon surfaces has been proposed and proved to increase significantly the stability. A study of the oxide relay mechanism at the surface revealed that the water-excluded environment of the active site in the reactive intermediate does not affect the key steps of this mechanism, in agreement with the experimental results reported. Next, the Ru(bda) has been shown to effectively catalyze the formation of molecular nitrogen from ammonia in an apolar solvent. The Ru(bda) has been well studied for water oxidation due to its high efficiency and the key step has been identified as the dimerization of two complexes driven by the aqueous solvent. The study of the dimerization process in acetonitrile has revealed the crucial role of solvent in supramolecular effects since acetonitrile promotes complex-counterion pairing aiding the dimerization of the Ru(bda) and. To increase the current density is needed a strategy to increase the catalyst density at the surface. Oligomerization of the Ru(tda) has shown to be an effective strategy to increase the current density of the hybrid electroanode to levels that are comparable to commercial electrolyzers. The exploration of the ways of attachment to the carbon surface revealed high dependency on the metal center oxidation state, the solvent, and the electric field. Also, the reactivity of the oligomer has been explored using the Empirical Valence Bond approach, revealing that the O-O bond formation remains unaltered in the oligomer and the reactivity remains unaltered in this complex environment, in agreement with experimental results. Finally, the substitution of the carboxylates in the Ru(tda) by phosphonates (Ru(tPaO)) has been proved to double the efficiency of the molecular catalyst at neutral pH. Due to the similarities between carboxylates and phosphonates the oxide relay mechanism has been tested in the Ru(tPaO), revealing that the origin of the extreme reactivity comes from low barriers in all the steps. The O-O bond formation involves an intramolecular radical coupling lowering the activation barrier to 2.1 kcal/mol. This radical coupling revealed a variation of the oxide relay mechanism called the radical oxide relay mechanism.
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| 5. |
- Juan Angel, de Gracia Triviño, 1989-, et al.
(författare)
-
Operando condition reaction modeling shows highly dynamic attachment of oligomeric ruthenium catalysts
- 2022
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Tidskriftsartikel (refereegranskat)abstract
- To increase the stability and current density of molecular-catalyst-based electroan- odes for water oxidation immobilization of the catalysts at the electrode surface is a common strategy. A prominent example it the oligomerized Ru(tda) molecular cat- alyst which showed outstanding current densities even at neutral pH values. One of the most challenging aspects of immobilized catalysts is to understand the interaction between the catalyst and the surface under operando conditions. Experiments are of- ten performed under model conditions and computational methods to study reaction steps are typically limited to a few hundred atoms. In this study, we combined three computational methods, density functional theory electronic structure computations, molecular dynamics for large scale simulations of the catalyst-solid interaction, and empirical valence bond for reaction modeling the catalyst at the interface of a large carbon support and a phosphate water buffer. These techniques allowed us to explore the combined effects of solvent, hydrophobic directionality, and electric field on the at- tachment and reactivity of a Ru(tda) pentamer at a graphene surface. Our simulations have perfect agreement with the experimental characterization under model conditions. However, we find that under operando conditions, where the catalyst is oxidized to the active RuV state, with a phosphate containing electrolyte and an applied electric field, the attachment is completely reversed compared to the model conditions with RuII and organic solvents. This reversed attachment leads to a water excluded region close to the active RuV=O center. The EVB reaction modeling showed that the reaction could still proceed to form an O-O bond via the oxide relay mechanism where a dangling carboxylate reacts with the oxo via nucleophilic attack. We find that the activation energy is identical in water solution and at the electrode surface, showing how this mechanism is key to highly active molecular water oxidation catalysts immobilized on surfaces. Since attachment to surfaces could have strong, and often negative, influence on the reactions this study provides a guideline in how to model reactions without compromising the complexity of the electrode environment.
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| 6. |
- Juan Angel, de Gracia Triviño, 1989-, et al.
(författare)
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Operando Condition Reaction Modeling Shows Highly Dynamic Attachment of Oligomeric Ruthenium Catalysts
- 2023
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 13:2, s. 1270-1279
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Tidskriftsartikel (refereegranskat)abstract
- To increase the stability and current density of molecular-catalyst-based electroanodes for water oxidation, immobilization of the catalysts at the electrode surface is a common strategy. A prominent example is the oligomerized Ru(tda) molecular catalyst, which showed outstanding current densities even at neutral pH values. One of the most challenging aspects of immobilized catalysts is to understand the interaction between the catalyst and the surface under operando conditions. Experiments are often performed under model conditions, and computational methods to study reaction steps are typically limited to a few hundred atoms. In this study, we combined three computational methods, density functional theory electronic structure computations, molecular dynamics for large-scale simulations of the catalyst-solid interaction, and empirical valence bond for reaction modeling the catalyst at the interface of a large carbon support and a phosphate water buffer. These techniques allowed us to explore the combined effects of solvent, hydrophobic directionality, and electric field on the attachment and reactivity of a Ru(tda) pentamer at a graphene surface. Our simulations have a perfect agreement with the experimental characterization under model conditions. However, we find that under operando conditions, where the catalyst is oxidized to the active RuV state, with a phosphate-containing electrolyte and an applied electric field, the attachment is completely reversed compared to the model conditions with RuII and organic solvents. This reversed attachment leads to a water-excluded region close to the active RuV═O center. The EVB reaction modeling showed that the reaction could still proceed to form an O-O bond via an oxide relay mechanism, where a dangling carboxylate reacts with the oxo via nucleophilic attack. We find that the activation energies are identical in water solution and at the electrode surface, showing how this mechanism is key to highly active molecular water oxidation catalysts immobilized on surfaces. Since attachment to surfaces could have a strong, and often negative, influence on the reactions, this study provides a guideline on how to model reactions without compromising the complexity of the electrode environment.
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| 7. |
- Juan Angel, de Gracia Triviño, 1989-, et al.
(författare)
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Oxide Relay: An Efficient Mechanism for Catalytic Water Oxidation at Hydrophobic Electrode Surfaces
- 2020
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:17, s. 7383-7387
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Tidskriftsartikel (refereegranskat)abstract
- In order to combine the advantages of molecular catalysts with the stability of solid-state catalysts, hybrid systems with catalysts immobilized on carbon nanotubes are prominent candidates. Here we explore our recent mechanistic proposal for Ru(tda)(py)2, the oxide relay mechanism, in a hybrid system from an experimental study. It reacts with the same efficiency but with increased stability compared to the homogeneous molecular catalyst. We used the empirical valence bond method and molecular dynamics with enhanced sampling approaches to investigate the two key steps in the mechanism: the intramolecular O–O bond formation and the OH– nucleophilic attack. The results on these calculations show that the oxide relay mechanism remains unaltered in the new environment. We believe that the principles should apply to other oxide containing dangling groups and to other metal centers, opening new possibilities of future developments on hybrid molecular catalyst-based water splitting devices.
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