| 1. |
- Corpas, Javier, et al.
(författare)
-
Interplay between the Directing Group and Multifunctional Acetate Ligand in Pd-Catalyzed anti-Acetoxylation of Unsymmetrical Dialkyl-Substituted Alkynes
- 2022
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 12:11, s. 6596-6605
-
Tidskriftsartikel (refereegranskat)abstract
- The cooperative action of the acetate ligand, the 2-pyridyl sulfonyl (SO2Py) directing group on the alkyne substrate,and the palladium catalyst has been shown to be crucial forcontrolling reactivity, regioselectivity, and stereoselectivity in theacetoxylation of unsymmetrical internal alkynes under mildreaction conditions. The corresponding alkenyl acetates wereobtained in good yields with complete levels of beta-regioselectivityandanti-acetoxypalladation stereocontrol. Experimental andcomputational analyses provide insight into the reasons behindthis delicate interplay between the ligand, directing group, and themetal in the reaction mechanism. In fact, these studies unveil themultiple important roles of the acetate ligand in the coordinationsphere at the Pd center: (i) it brings the acetic acid reagent into close proximity to the metal to allow the simultaneous activation ofthe alkyne and the acetic acid, (ii) it serves as an inner-sphere base while enhancing the nucleophilicity of the acid, and (iii) it acts asan intramolecular acid to facilitate protodemetalation and regeneration of the catalyst. Further insight into the origin of the observedregiocontrol is provided by the mapping of potential energy profiles and distortion-interaction analysis
|
|
| 2. |
- Corpas, Javier, et al.
(författare)
-
Iterative Dual-Metal and Energy Transfer Catalysis Enables Stereodivergence in Alkyne Difunctionalization: Carboboration as Case Study
- 2023
-
Ingår i: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435. ; 13:22, s. 14914-14927
-
Tidskriftsartikel (refereegranskat)abstract
- Stereochemically defined tetrasubstituted olefins are widespread structural elements of organic molecules and key intermediates in organic synthesis. However, flexible methods enabling stereodivergent access to E and Z isomers of fully substituted alkenes from a common precursor represent a significant challenge and are actively sought after in catalysis, especially those amenable to complex multifunctional molecules. Herein, we demonstrate that iterative dual-metal and energy transfer catalysis constitutes a unique platform for achieving stereodivergence in the difunctionalization of internal alkynes. The utility of this approach is showcased by the stereodivergent synthesis of both stereoisomers of tetrasubstituted beta-boryl acrylates from internal alkynoates with excellent stereocontrol via sequential carboboration and photoisomerization. The reluctance of electron-deficient internal alkynes to undergo catalytic carboboration has been overcome through cooperative Cu/Pd-catalysis, whereas an Ir complex was identified as a versatile sensitizer that is able to photoisomerize the resulting sterically crowded alkenes. Mechanistic studies by means of quantum-chemical calculations, quenching experiments, and transient absorption spectroscopy have been applied to unveil the mechanism of both steps.
|
|
| 3. |
- Fernandez-Benito, Amparo, et al.
(författare)
-
Green and Scalable Biopolymer-Based Aqueous Polyelectrolyte Complexes for Zinc-Ion Charge Storage Devices
- 2023
-
Ingår i: ChemElectroChem. - : WILEY-V C H VERLAG GMBH. - 2196-0216. ; 10:2
-
Tidskriftsartikel (refereegranskat)abstract
- Green and scalable materials are essential to fulfill the need of electrification for transitioning into a fossil-fuels free society, and sustainability is a requirement for all new technologies. Rechargeable batteries are one of the most important elements for electrification, enabling the transition to mobile electronics, electrical vehicles and grid storage. We here report synthesis and characterization of polyelectrolyte complexes of alginate and chitosan, both biopolymers deriving from the sea, for transport of zinc ions in hydrogel electrolytes. We have used vibrational spectroscopy, thermal measurements and microscopy, as well as transport measurements with ohmic or blocking contacts. The transference number for zinc ions is close to 1, the conductivity is approximate to 10 mS/cm, with stability at Zn interfaces seen through 7000 cycles in symmetric zinc//zinc cell. A zinc ion aqueous electrolyte was prepared from blends of chitosan and alginate, by using a simple and scalable route. These green zinc ion electrolytes exhibit a stability window up to 2 V, a zinc ion transference number close to 1, and electrochemical cyclability over 7000 cycles at interfaces to zinc. This biologically derived polyelectrolyte complex offers many possibilities for optimizing transport and stability at electrode interfaces.image
|
|
| 4. |
- Liu, Tao, et al.
(författare)
-
Understanding LiOH Formation in a Li-O2 Battery with LiI and H2O Additives
- 2019
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 9:1, s. 66-77
-
Tidskriftsartikel (refereegranskat)abstract
- LiI-promoted LiOH formation in Li-O2 batteries with wet ether electrolytes has been investigated by Raman, nuclear magnetic resonance spectroscopy, operando pressure tests, and molecular dynamics simulations. We find that LiOH formation is a synergistic effect involving both H2O and LiI additives, whereas with either alone Li2O2 forms. LiOH is generated via a nominal four-electron oxygen reduction reaction, the hydrogen coming from H2O and the oxygen from both O2 and H2O, and with fewer side reactions than typically associated with Li2O2 formation; the presence of fewer parasitic reactions is attributed to the proton donor role of water, which can coordinate to O2- and the higher chemical stability of LiOH. Iodide plays a catalytic role in decomposing H2O2/HO2- and thereby promoting LiOH formation, its efficacy being highly dependent on the water concentration. This iodide catalysis becomes retarded at high water contents due to the formation of large water-solvated clusters, and Li2O2 forms again.
|
|
| 5. |
- Navarro Suárez, Adriana, 1983, et al.
(författare)
-
Development of asymmetric supercapacitors with titanium carbide-reduced graphene oxide couples as electrodes
- 2018
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 259, s. 752-761
-
Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) nanomaterials have attracted significant interest for supercapacitor applications due to their high surface to volume ratio. Layered 2D materials have the ability to intercalate ions and thus can provide intercalation pseudocapacitance. Properties such as achieving fast ion diffusion kinetics and maximizing the exposure of the electrolyte to the surface of the active material are critical for optimizing the performance of active materials for electrochemical capacitors (i.e. Supercapacitors). In this study, two 2D materials, titanium carbide (Ti 3 C 2 T x ) and reduced graphene oxide (rGO), were used as electrode materials for asymmetric supercapacitors, with the resulting devices achieving high capacitance values and excellent capacitance retention in both aqueous and organic electrolytes. This work demonstrates that Ti 3 C 2 T x is a promising electrode material for flexible and high-performance energy storage devices.
|
|
| 6. |
- Navarro Suárez, Adriana, 1983, et al.
(författare)
-
Poly(quinone-amine)/nanocarbon composite electrodes with enhanced proton storage capacity
- 2017
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 5:44, s. 23292-23298
-
Tidskriftsartikel (refereegranskat)abstract
- Novel redox active bi- and terpolymers, containing quinone-amine blocks and wired by nanocarbons have been synthesized and studied as negative electrodes for electrochemical proton storage. Two kinds of diamine (aliphatic and aromatic) were condensed with benzoquinone to enhance the storage capacity. The reaction between the benzoquinone and the diamines created an electroactive polymer displaying pseudo-faradaic proton transfer processes. Besides this transfer process, the aromatic diamine showed an additional reversible redox reaction, between the nitrogen atoms conjugated to the quinone molecule and the hydrogen ions. The incorporation of carbon conductive nanofillers with specific dimensionality provided an additional and straightforward strategy to maximize both the electron conductivity and the proton storage capacity of the polymers. Homogeneous dispersion of nanocarbon redox polymer particles in the composite (along with the creation of a polymer-carbon interphase) was essential, in order to maximize the proton storage capacity. A clear correlation between the nanostructure of the polymer particles, the dimensionality of the nanocarbons and the polymerization process was found. These low-cost redox polymers reached up to 230 mA h g-1 and 75 ?A h cm-2 at 0.08 A g-1 in an aqueous-based electrolyte, paving the way for the use of these materials for technologies such as thin-film devices and grid energy storage.
|
|
| 7. |
- Navarro Suárez, Adriana, 1983, et al.
(författare)
-
Temperature effect on the synthesis of lignin-derived carbons for electrochemical energy storage applications
- 2018
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 397, s. 296-306
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, we present a detailed study by N2 sorption and Small Angle X-ray Scattering (SAXS) of the carbonization and KOH activation of lignin for its application as active material for electrochemical energy storage. It has been observed that i) the carbonization of lignin above 700 °C leads to a hard carbon with a large amount of bulk (buried) fine structure microporosity and a good performance as Na-ion negative electrode, ii) when KOH activation is done after complete carbonization it is mainly increasing the accessibility of the initial bulk microporosity, leading to a carbon with good performance as symmetric supercapacitor in aqueous electrolyte and iii) when carbonization and KOH activation are done simultaneously, a distinct pore structure is generated with a large amount of mesopores, suitable for symmetric supercapacitor in organic electrolyte. By combining SAXS, which is sensitive to bulk as well as surface porosity, and N2 sorption which probes surface porosity, it has been possible to follow the intricate mechanism of microporosity development. Finally, it is believed that these results can be extrapolated to various biomass based precursors.
|
|
| 8. |
- Zhao, Evan Wenbo, et al.
(författare)
-
In situ NMR metrology reveals reaction mechanisms in redox flow batteries
- 2020
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 579:7798, s. 224-228
-
Tidskriftsartikel (refereegranskat)abstract
- Large-scale energy storage is becoming increasingly critical to balancing renewable energy production and consumption1. Organic redox flow batteries, made from inexpensive and sustainable redox-active materials, are promising storage technologies that are cheaper and less environmentally hazardous than vanadium-based batteries, but they have shorter lifetimes and lower energy density2,3. Thus, fundamental insight at the molecular level is required to improve performance4,5. Here we report two in situ nuclear magnetic resonance (NMR) methods of studying redox flow batteries, which are applied to two redox-active electrolytes: 2,6-dihydroxyanthraquinone (DHAQ) and 4,4′-((9,10-anthraquinone-2,6-diyl)dioxy) dibutyrate (DBEAQ). In the first method, we monitor the changes in the 1H NMR shift of the liquid electrolyte as it flows out of the electrochemical cell. In the second method, we observe the changes that occur simultaneously in the positive and negative electrodes in the full electrochemical cell. Using the bulk magnetization changes (observed via the 1H NMR shift of the water resonance) and the line broadening of the 1H shifts of the quinone resonances as a function of the state of charge, we measure the potential differences of the two single-electron couples, identify and quantify the rate of electron transfer between the reduced and oxidized species, and determine the extent of electron delocalization of the unpaired spins over the radical anions. These NMR techniques enable electrolyte decomposition and battery self-discharge to be explored in real time, and show that DHAQ is decomposed electrochemically via a reaction that can be minimized by limiting the voltage used on charging. We foresee applications of these NMR methods in understanding a wide range of redox processes in flow and other electrochemical systems.
|
|
