7 Search Results

The title compounds were prepared via a wet chemistry route and their crystal structures were determined from single crystal X-ray diffraction data. Na₂Mn(SO₄)₂·4H₂O crystallizes with a monoclinic symmetry, space group P2₁/c, with a = 5.5415(2), b = 8.3447(3), c = 11.2281(3) Å, β = 100.172(1)°, V = 511.05(3) ų and Z = 2. Na₂Ni(SO₄)₂·10H₂O also crystallizes with a monoclinic symmetry, space group P2₁/c, with a = 12.5050(8), b = 6.4812(4), c = 10.0210(6) Å, β = 106.138(2)°, V = 780.17(8) Å3 and Z = 2. Na₂Mn(SO₄)₂·4H₂O is a new member of the blödite family of compounds, whereas Na₂Ni(SO₄)₂·10H₂O is isostructuralmore » with Na₂Mg(SO₄)₂·10H₂O. The structure of Na₂Mn(SO₄)₂·4H₂O is built up of [Mn(SO₄)₂(H₂O)₄]^2– building blocks connected through moderate O–H…O hydrogen bonds with the sodium atoms occupying the large tunnels along the a axis and the manganese atom lying on an inversion center, whereas the structure of Na₂Ni(SO₄)₂·10H₂O is built up of [Ni(H₂O)₆]²⁺ and [Na₂(SO₄)₂(H₂O)₄]^2– layers. These layers which are parallel to the (100) plane are interconnected through moderate O–H…O hydrogen bonds. Here, the thermal gravimetric- and the powder X-ray diffraction-analyzes showed that only the nickel phase was almost pure. At a temperature above 300 °C, all the water molecules evaporated and a structural phase transition from P2₁/c-Na₂Ni(SO₄)₂·10H₂O to C2/c-Na₂Ni(SO₄)₂ was observed. C2/c-Na₂Ni(SO₄)₂ is thermally more stable than Na₂Fe(SO₄)₂ and therefore it would be suitable as the positive electrode for sodium ion batteries if a stable electrolyte at high voltage is developed.« less

Four novel TPDCA derivatives were prepared via a supersaturation method combining TPDCA with water, N-methyl-2-pyrrolidone (NMP), Na(PO₂H₂), and ammonia solution: 2(C₉H₇NO₅S)H₂O (1), (C₉H₇NO₅S)C₅H₉NO (2), (C₉H₇NO₅S)Na(PO₂H₂) (3), and (C₉H₅NO₅S)(NH₄)2(H₂O) (4). Their crystal structures were determined by single-crystal X-ray diffraction. Compounds (1) and (2) crystallize in the monoclinic space groups P2₁ and P2₁/c, respectively, whereas compounds (3) and (4) crystallize in the triclinic space group P1^-. Weak and moderate hydrogen bonds were detected in the four compounds. In the biological tests, (1) and (3) exhibited significant antibacterial activity against Escherichia coli and Staphylococcus aureus; in addition, (1) was cytotoxic against leukemia HL-60more » cells with the IC₅₀ value of 158.5 ± 12.5 μM.« less

Sodium (Na) super ionic conductor (NASICON) polyanionic compounds have recently attracted much attention from the battery community because of their electroactive properties and reasonably high ionic conductivities, leading to their use as a cathode in sodium-ion batteries. This article describes the compositional optimizations, crystallographic evaluations, and electrochemical behavior of a new mixed NASICON polyanionic compound, NaFe_2-xV_x(PO₄)(SO₄)₂. By doping the characteristic Fe³⁺ sites of the FeO₆ octahedrons with varying amounts of V³⁺, the electrochemical stability and charge transport in NaFe₂(PO₄)(SO₄)₂ were enhanced. The resulting best composition, with crystal structure NaFe_1.4V_0.6(PO₄)(SO₄)₂ resolved through the Rietveld method, exhibited a stable capacity compared withmore » the other synthesized compositions. In situ powder x-ray diffraction measurements, a single-phase intercalation/deintercalation mechanism of the NASICON structure in the measured sodium concentration window was observed with no impurity phase formation. Further electrochemical assessments revealed the interfacial charge transfer kinetics to be the rate-limiting step in the sodium concentration window. Also, the measured sodium-ion diffusivity values in the range of 6 × 10^-11 to 7 × 10^-11 cm²/s in the measured sodium concentration range. The results reported here highlight the potential of compositionally and morphologically optimized NaFe_1.4V_0.6(PO₄)(SO₄)₂ with higher particle surface areas as a cathode material for high-performance sodium-ion batteries.« less

We report on the successful synthesis of diammonium magnesium dihydrogendiphosphate (V) dihydrate compound (NH₄)₂Mg(H₂P₂O₇)₂•2H₂O using a wet chemical route. Single crystal X-ray diffraction analysis and micro Raman spectroscopy are employed to characterize the compound. We demonstrate, using a multidisciplinary approach, that this compound is ideal for carbon dioxide (CO₂) capture in addition to other anthropogenic gasses. We show here -from both an experimental as well as from a density functional theory (DFT) calculations routes- the potential for adopting this compound into domestic air-conditioning units (ACUs). From these experiments, the resistance to bacterial growth is also investigated, which is critical formore » the adoption of this compound in ACUs. Our compound exhibits a higher methane (CH₄) sorptivity as compared to CO₂ at 25 °C and 45 °C under pressures up to 50 bars. Furthermore, DFT electronic structure calculations are used to compute the main structural and electronic properties of the compound, taking into consideration the characteristics of the identified pores as a function of the progressive CO₂ vs. CH₄ loadings. Finally, the antibacterial assay reveals a strong antibacterial activity against the tested Gram-positive and Gram-negative bacteria, with a large zone of inhibition against the tested E. Coli, S. Aureus and K. Pneumonia« less

Excellent structural stability, high operating voltage, and high capacity have made Na₃V₂(PO₄)₂F₃ a promising cathode material for sodium-ion batteries. However, high-temperature battery performances and heat generation measurements have not been systematically reported yet. Carbon-coated Na₃V₂(PO₄)₂F₃@MWCNT (multi-walled carbon nanotube) samples are fabricated by a hydrothermal-assisted sol-gel method and the electrochemical performances are evaluated at three different temperatures (25, 45, and 55 °C). Furthermore, the well-crystallized Na₃V₂(PO₄)₂F₃@MWCNT samples exhibit good cycling stability at both low and high temperatures; they deliver an initial discharge capacity of 120–125 mAhg^-1 at a 1 C rate with a retention of 53 % capacity after 1,400 cyclesmore » with 99 % columbic efficiency. The half-cell delivers a capacity of 100 mAhg^-1 even at a high rate of 10 C at room temperature. Furthermore, the Na₃V₂(PO₄)₂F₃@MWCNT samples show good long-term durability; the capacity loss is an average of 0.05 % per cycle at a 1 C rate at 55 °C. Additionally, ionic diffusivity and charge transfer resistance are evaluated as functions of state of charge, and they explain the high electrochemical performance of the Na₃V₂(PO₄)₂F₃@MWCNT samples. In-situ heat generation measurements reveal reversible results upon cycling owing to the high structural stability of the material. Excellent electrochemical performances are also demonstrated in the full-cell configuration with hard carbon as well as antimony Sb/C anodes.« less

The electrochemical community around the world is focusing heavily on sodium-ion batteries R&D due to the huge abundance of sodium and need for large scale deployment of safe and inexpensive batteries for the electrical grid energy storage. Here, we observe the characterization of model parameters such as ionic diffusivity and interfacial kinetics, for a potential sodium-ion battery cathode material, Na₂-_xFe₃(PO₄)₃, using experimental and computational investigations. The Na₂-_xFe₃(PO₄)₃ structure is characterized by two distinct one-dimensional (1-D) Na diffusion channels. Density Functional Theory (DFT) calculation reveals that Na is first fully removed from one of the channels followed by the subsequent removalmore » of Na from the second channel. The experimental exploration reveals that, in the beginning of Na removal at 0 ≤ x ≤ 0.5; the sodium ion diffusivity is of the order of ~10^–11 cm²s^–1 and then slightly decreases. This is further confirmed by comparing the calculated sodium diffusion barriers along the individual 1-D channels as well as between the channels. Nevertheless, the exchange current density slowly increases up to x=1.0 and remains quite constant thereafter. The magnitude of exchange current density is very low suggesting that the interfacial kinetics are the rate limiting factor. The obtained results indicate that Na₂-_xFe₃(PO₄)₃ could achieve better rate performance with long cycling stability through engineering of the particle morphology and microstructure.« less

The compound NaFe₂(PO₄)(SO₄)₂ is successfully synthesized via a solid state reaction route and its crystal structure is determined using powder X-ray diffraction data. NaFe₂(PO₄)(SO₄)₂ phase is also characterized by cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. NaFe₂(PO₄)(SO₄)₂ crystallizes with the well-known NASICON-type structure. SAED and HRTEM experiments confirm the structural model, and no ordering between the PO₄^-3 and SO₄^-2 polyanions is detected. The electrochemical tests indicate that NaFe₂(PO₄)(SO₄)₂ is a 3 V sodium intercalating cathode. The electrical conductivity is relatively low (2.2 × 10^-6 Scm^-1 at 200 °C) and the obtained activation energy is ~0.60eV. The GITT experiments indicatemore » that the diffusivity values are in the range of 10^-11-10^-12 cm²/s within the measured sodium concentrations.« less