| 1. |
- Etman, Ahmed S., et al.
(författare)
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Insights into the Exfoliation Process of V2O5· nH2O Nanosheet Formation Using Real-Time 51V NMR
- 2019
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:6, s. 10899-10905
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Tidskriftsartikel (refereegranskat)abstract
- Copyright © 2019 American Chemical Society. Nanostructured hydrated vanadium oxides (V2O5·nH2O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5·nH2O nanosheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5·nH2O nanosheets from the V2O5 and VO2 precursors in real time using solution- and solid-state 51V NMR. Solution-state 51V NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28]4- and the hydrated dioxovanadate cation [VO2·4H2O]+, and during the exfoliation process, decavanadate was formed, while the amount of [VO2·4H2O]+ remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state 51V NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5·nH2O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state 51V signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials. ©
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| 2. |
- Wang, Lei, et al.
(författare)
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A nickel (II) PY5 complex as an electrocatalyst for water oxidation
- 2016
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 335, s. 72-78
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Tidskriftsartikel (refereegranskat)abstract
- A Ni-PY5 [PY5 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine)] complex has been found to act as an electrocatalyst for oxidizing water to dioxygen in aqueous phosphate buffer solutions. The rate of water oxidation catalyzed by the Ni-PY5 is remarkably enhanced by the proton acceptor base HPO42-, with rate constant of 1820 M-1 s(-1). Controlled potential bulk electrolysis with Ni-PY5 at pH 10.8 under an applied potential of 1.5 V vs. normal hydrogen electrode (NHE) resulted in dioxygen formation with a high faradaic efficiency over 90%. A detailed mechanistic study identifies the water nucleophilic attack pathway for water oxidation catalysis.
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| 3. |
- Xu, Bo, 1980-, et al.
(författare)
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Solution-processed nanoporous NiO-dye-ZnO photocathodes : Toward efficient and stable solid-state p-type dye-sensitized solar cells and dye-sensitized photoelectrosynthesis cells
- 2019
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855 .- 2211-3282. ; 55, s. 59-64
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Tidskriftsartikel (refereegranskat)abstract
- A solution-processed NiO-dye-ZnO photocathode was developed for applications in both solid-state p-type dye-sensitized solar cells (p-ssDSCs) and p-type dye-sensitized photoelectrosynthesis cells (p-DSPECs). In p-ssDSCs, the solar cell using ZnO as electron transport material showed a short circuit current, up to 680 mu A cm(-2), which is 60-fold larger than that previously reported device using TiO2 as electron transport material with similar architecture. In the p-DSPECs, a remarkable photocurrent of 100 mu A cm(-2) was achieved in a pH = 5.0 acetate buffer solution under a bias potential at 0.05 V vs RHE with platinum as the proton reduction catalyst. A Faradaic efficiency approaching 100% for the H-2 evolution reaction was obtained after photoelectrolysis for 9 h. Importantly, the solution-processed NiO-dye-ZnO photocathode exhibited excellent long-term stability in both p-ssDSCs and p-DSPECs. To the best of our knowledge, this is the first study where a solution-processable, nanoporous NiO-dye-ZnO photocathode is used for both p-ssDSCs and p-DSPECs having both excellent device performance and stability.
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| 4. |
- Chen, Hong, et al.
(författare)
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Construct Polyoxometalate Frameworks through Covalent Bonds
- 2015
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 54:17, s. 8699-8704
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Tidskriftsartikel (refereegranskat)abstract
- An emerging strategy for exploring the application of polyoxometalates (POMs) is to assemble POM clusters into open-framework materials, especially inorganic organic hybrid three-dimensional (3D) open-framework materials, via the introduction of different organic linkers between the POM clusters. This strategy has yielded a few 3D crystalline POMs of which a typical class is the group of polyoxometalate metal organic frameworks (POMMOFs). However, for reported POMMOFs, only coordination bonds are involved between the linkers and POM clusters, and it has not yet produced any covalently bonded polyoxometalate frameworks. Here, the concept of "covalently bonded POMs (CPOMs)" is developed. By using vanadoborates as an example, we showed that the 3D CPOMs can be obtained by a condensation reaction through the oxolation mechanism of polymer chemistry. In particular, suitable single crystals were harvested and characterized by single-crystal X-ray diffraction. This work forges a link among polymer science, POM chemistry, and open-framework materials by demonstrating that it is possible to use covalent bonds according to polymer chemistry principles to construct crystalline 3D open-framework POM materials.
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| 5. |
- Etman, Ahmed, et al.
(författare)
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A Water Based Synthesis of Ultrathin Hydrated Vanadium Pentoxide Nanosheets for Lithium Battery Application : Free Standing Electrodes or Conventionally Casted Electrodes?
- 2017
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 252, s. 254-260
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Ultrathin hydrated vanadium pentoxide (V2O5·nH2O) nanosheets are fabricated via a water based exfoliation technique. The exfoliation process involves reflux of the precursor, 1:4 mixture of VO2 and V2O5, in water at 80 °C for 24 h. Operando and ex situ X-ray diffraction (XRD) studies are conducted to follow the structural changes during the exfoliation process. The chemical and thermal analyses suggest that the molecular formula of the nanosheet is H 0.2 V 1.8 V V 0.2 IV O 5 ⋅ 0.5 H 2 O . The V2O5·nH2O nanosheets are mixed with 10% of multi-walled carbon nanotube (MW-CNT) to form a composite material assigned as (VOx-CNT). Free standing electrodes (FSE) and conventionally casted electrodes (CCE) of VOx-CNT are fabricated and then tested as a positive electrode material for lithium batteries. The FSE shows reversible capacities of 300 and 97 mAhg-1 at current densities of 10 and 200 mAhg-1, respectively. This is better than earlier reports for free-standing electrodes. The CCE delivers discharge capacities of 175 and 93 mAhg-1 at current densities of 10 and 200 mAhg-1, respectively.
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| 6. |
- Etman, Ahmed S., et al.
(författare)
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Insights into the Exfoliation Process of V2O5 center dot nH(2)O Nanosheet Formation Using Real-Time V-51 NMR
- 2019
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:6, s. 10899-10905
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured hydrated vanadium oxides (V2O5 center dot nH(2)O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5 center dot nH(2)O nano-sheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5 center dot nH(2)O nanosheets from the V2O5 and VO2 precursors in real using solution- and solid-state V-51 NMR. Solution-state V-51 NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28](4-) and the hydrated dioxova-nadate cation [VO2 center dot 4H(2)O](+), and during the exfoliation process, decavanadate was formed, while the amount of [VO2 center dot 4H(2)O](+) remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state V-51 NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5 center dot nH(2)O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state V-51 signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials.
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| 7. |
- Etman, Ahmed S., et al.
(författare)
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V2O5·nH2O nanosheets and multi-walled carbon nanotube composite as a negative electrode for sodium-ion batteries
- 2019
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Ingår i: Journal of Energy Chemistry. - : Elsevier BV. - 2095-4956 .- 2096-885X. ; 30, s. 145-151
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Tidskriftsartikel (refereegranskat)abstract
- Two dimensional (2D) transition metal oxides and chalcogenides demonstrate a promising performance in sodium-ion batteries (SIBs) application. In this study, we investigated the use of a composite of freeze dried V2O5·nH2O nanosheets and multi-walled carbon nanotube (MWCNT) as a negative electrode material for SIBs. Cyclic voltammetry (CV) results indicated that a reversible sodium-ion insertion/deinsertion into the composite electrode can be obtained in the potential window of 0.1–2.5 V vs. Na+/Na. The composite electrodes delivered sodium storage capacities of 140 and 45 mAh g−1 under applied current densities of 20 and 100 mA g−1, respectively. The pause test during constant current measurement showed a raise in the open circuit potential (OCP) of about 0.46 V, and a charge capacity loss of ∼10%. These values are comparable with those reported for hard carbon electrodes. For comparison, electrodes of freeze dried V2O5·nH2O nanosheets were prepared and tested for SIBs application. The results showed that the MWCNT plays a significant role in the electrochemical performance of the composite material.
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| 8. |
- Fan, Ke, et al.
(författare)
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Immobilization of a Molecular Ruthenium Catalyst on Hematite Nanorod Arrays for Water Oxidation with Stable Photocurrent
- 2015
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 8:19, s. 3242-3247
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectrochemical (PEC) cells for light-driven water splitting are prepared using hematite nanorod arrays on conductive glass as the photoanode. These devices improve the photocurrent of the hematite-based photoanode for water splitting, owing to fewer surface traps and decreased electron recombination resulting from the one-dimensional structure. By employing a molecular ruthenium co-catalyst, which contains a strong 2,6-pyridine-dicarboxylic acid anchoring group at the hematite photoanode, the photocurrent of the PEC cell is enhanced with high stability for over 10000s in a 1M KOH solution. This approach can pave a route for combining one-dimensional nanomaterials and molecular catalysts to split water with high efficiency and stability.
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| 9. |
- Gao, Weiming, et al.
(författare)
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Attachment of a Hydrogen-Bonding Carboxylate Side Chain to an FeFe -Hydrogenase Model Complex : Influence on the Catalytic Mechanism
- 2010
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Ingår i: Chemistry - A European Journal. - Weinheim : Wiley. - 0947-6539 .- 1521-3765. ; 16:8, s. 2537-2546
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Tidskriftsartikel (refereegranskat)abstract
- Azapropanedithiolate (adt)-bridged model complexes of [FeFe]-hydrogenase bearing a carboxylic acid functionality have been designed with the aim of decreasing the potential for reduction of protons to hydrogen. Protonation of the bisphosphine complexes 4-6 has been studied by in situ IR and NMR spectroscopy, which revealed that protonation with triflic acid most likely takes place first at the N-bridge for complex 4 but at the Fe Fe bond for complexes 5 and 6. Using an excess of acid, the diprotonated species could also be observed, but none of the protonated species was sufficiently stable to be isolated in a pure state. Electrochemical studies have provided an insight into the catalytic mechanisms under strongly acidic conditions, and have also shown that complexes 3 and 6 are electro-active in aqueous solution even in the absence of acid, presumably due to hydrogen bonding. Hydrogen evolution, driven by visible light, has been observed for three-component systems consisting of [Ru(bpy)(3)](2+), complex 1, 2, or 3, and ascorbic acid in CH3CN/D2O solution by on-line mass spectrometry.
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| 10. |
- Han, Lei, et al.
(författare)
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Two Isomeric Magnesium Metal-Organic Frameworks with [24-MC-6] Metallacrown Cluster
- 2013
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 13:5, s. 1807-1811
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Tidskriftsartikel (refereegranskat)abstract
- Two novel Mg-based metal-organic framework isomers with the formula [Mg-2(HCO2)(2)(NH2-BDC)-(DMF)(2)](n) (NH2-BDC = 2-amino-1,4-benzenedicarboxylate) have been synthesized based on a 6-connected [24-MC-6] metallacrown secondary building unit (SBU), which display a two-dimensional (2D) 3(6) net (1) and three-dimensional primitive rhombohedral net (2) derived from a different extended orientation of SBU, respectively. The 2D framework of 1 exhibits relevant thermal stability, solvents stability, high CO2 adsorption, and strong luminescent properties.
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