Collisional deactivation of O2(1Σg+)

Relaxation rates for O₂(¹Σ_g⁺) by nonradiative pathways have been determined using the fast-flow technique. O₂(¹Σ_g⁺) is formed from O₂(¹Δ_g) by an energy pooling process. O₂(¹Δ_g) is generated by passing purified oxygen through a microwave discharge. Oxygen atoms are removed by distilling mercury vapor through the discharge zone. It has been observed that the wall loss rate for O₂(¹Σ_g⁺) decreases with increasing pressure of oxygen and thus appears to be diffusion controlled. Quenching rate constants for O₂, N₂, and He have been determined and found to be (1.5 ± 0.1) × 10⁴, (1.0 ± 0.05) × 10⁶ and (1.2 ± 0.1) × 10⁵ l./mol·sec, respectively.     

Modeling Chemical Composition for an Atmospheric Pressure DC Discharge in Air with Water Cathode by 0-D model

This paper reports the results of the chemical composition modeling for an atmospheric pressure DC air discharge with water cathode. The modeling was based on the combined solution of Boltzmann equation for electrons, equations of vibrational kinetics for ground states of N₂, O₂, H₂O and NO molecules, equations of chemical kinetics and plasma conductivity equation. Calculations were carried out using experimental values of E/N and gas temperatures for the discharge currents range of 20–50 mA. The effect of H₂O concentration on the plasma composition was studied. The main particles of plasma were shown to be O₂(a¹Δ, b¹Σ), O(³P), NO, NO₂, HNO₃, H₂O₂ and OH. Effective vibrational temperatures of molecules were higher than gas temperature and they did not depend on the discharge current. Distribution functions on vibrational levels for N₂, O₂, H₂O and NO ground states were non-equilibrium ones.     

Effect of solvents on the morphology of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript>/graphene nanostructures for electrochemical pseudocapacitor application

The large internal surface areas and outstanding electrical and mechanical properties of graphene have prompted to blend graphene with NiCo₂O₄ to fabricate nanostructured NiCo₂O₄/graphene composites for supercapacitor applications. The use of graphene as blending with NiCo₂O₄ enhances the specific capacitance and rate capability and improves the cyclic performance when compared to the pristine NiCo₂O₄ material. Here, we synthesized two different nanostructured morphologies of NiCo₂O₄ on graphene sheets by solvothermal method. It has been suggested that the morphologies of oxides are greatly influenced by dielectric constant, thermal conductivity, and viscosity of solvents employed during the synthesis. In order to test this concept, we have synthesized nanostructured NiCo₂O₄ on graphene sheets by facile solvothermal method using N-methyl pyrrolidone and N,N-dimethylformamide solvents with water. We find that mixture of N-methyl pyrrolidone and water solvent favored the formation of nanonet-like NiCo₂O₄/graphene (NiCoO-net) whereas mixture of N,N-dimethylformamide and water solvent produced microsphere-like NiCo₂O₄/graphene (NiCoO-sphere). Electrochemical pseudocapacitance behavior of the two NiCo₂O₄/graphene electrode materials was studied by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy techniques. The supercapacitance measurements on NiCoO-net and NiCoO-sphere electrodes showed specific capacitance values of 1060 and 855 F g^?1, respectively, at the current density of 1.5 A g^?1. The capacitance retention of NiCoO-net electrode is 93 % while that of NiCoO-sphere electrode is 77 % after long-term 5000 charge-discharge cycles at high current density of 10 A g^?1.     

Yields of O2(1Σg+) and O2(1Δg) in the H + O2 reaction system,and the quenching of O2(1Σg+) by atomic hydrogen

The generation of metastable O₂(¹Σg⁺) and O₂(¹Δg) in the H + O₂ system of reactions was studied by the flow discharge chemiluminescence detection method. In addition to the O₂(¹Σg⁺) and O₂(¹Δg) emissions, strong OH(v = 2) → OH(v = 0), OH(v = 3) → OH(v = 1), HO₂(²A′₀₀₀) → HO₂(²A″₀₀₀), HO₂(²A′₀₀₁) → HO₂(²A″₀₀₀), and H O₂(²A″₂₀₀) → HO₂(²A″₀₀₀) emissions were detected in the H + O₂ system. The rate constants for the quenching of O₂(¹Σg⁺) by H and H₂ were determined to be (5.1 ± 1.4) × 10^?13 and (7.1 ± 0.1) × 10^?13 cm³ s^?1, respectively. An upper limit for the branching ratio to produce O₂(¹Σg⁺) by the H + HO₂ reaction was calculated to be 2.1%. The contributions from other reactions producing singlet oxygen were investigated.     

Induction of radiative forbidden transitions in an oxygen molecule in O<Subscript>2</Subscript>–H<Subscript>2</Subscript>O collision complexes

By the DFT/B3LYP method the equilibrium structures of oxygen complexes with water are calculated in various geometric conformations with symmetries C _2v and C _s . By the MRCI/CASSCF method potential energy surface cross-sections of the ^1.3[O₂–H₂O] complexation reaction are constructed. With taking into account the spin-orbit coupling, the forbidden transition moments a ¹Δ _g –X ³Σ _g ^?, b ¹Σ _g ⁺–a ¹Δ _g , c ¹Σ _u ^?–a ¹Δ _g , A ³Σ _u ⁺–X ³Σ _g ^? of the complexes are calculated and changes in their intensities at different geometric configurations of the complex are revealed.     

The first two structurally characterized energetic catalysts derived from dinitropyridone

Two energetic catalysts, 3,5-dinitro-2-pyridonate of lead (II) (Pb(2DNPO)₂, 1) and 3,5-dinitro-4-pyridone-N-hydroxylate tetrahydrate of copper (II) (Cu(4DNPOH)₂(H₂O)₄, 2) were characterized by elemental analysis, FT-IR, TG-DSC and structurally characterized by X-ray single-crystal diffraction analysis. X-ray powder diffraction analysis of complex 1 confirmed the phase homogeneity of the polycrystalline sample. Crystal data for 1: monoclinic, space group P 21/n, a = 8.5253(9), b = 9.2938(10), c = 19.654(2) Å, β = 102.289(2)°, V = 1521.6(3) ų, Z = 4; 2: monoclinic, space group P 21/n , a = 8.3705(10), b = 9.9307(12), c = 10.5771(12) Å, β = 98.021(2)°, V = 870.62(18) ų, Z = 2. The complex 1 is a one-dimensional coordination polymer with each Pb(II) atom being six-coordinated, forming a heavily distorted octahedral geometry, by two nitrogen and four oxygen donors. Each ligand links the Pb(II) ions in a chelating bridging mode using nitrogen and oxygen atoms of its pyridonate part. The complex 2 is a copper (II) complex with a compressed octahedral geometry. The Cu(II) atom locates on the equatorial positions defined by oxygen atoms of four water molecules. Its axial positions are filled with two oxygen donors of the pyridine-N-hydroxylate moieties of two ligands. The abundant hydrogen bonds link the molecules into one-dimensional chains. Both the complexes represent the first two examples of the energetic catalysts containing dinitropyridine derivatives characterized crystallographically     

The nature of molecular oxygen binding and activation in Mn-O2 complex

Non-empirical calculations of CASSCF energies, electric dipole moments, Einstein coefficients, matrix elements of the operator of spin-orbital interaction between states of different multiplicity in a model complex ^6,8[Mn-O₂] of C _2v symmetry have been made in 3-21G, 6-31G, 6-31G** basis sets. The crosssections of the potential energy surface (PES) of the ground and excited states were built. It is found that oxygen bonding to manganese is possible when excited atoms of manganese collide with molecular oxygen, singlet oxygen with Mn[⁶ S _5/2] atoms, or in a close contact O₂[X³Σ _g ^? ] + Mn[⁶ S _5/2] and is determined by charge transfer states ^6,8CTS(Mn⁺O ₂ ^? ). Mechanisms of singlet oxygen activation/deactivation are determined by a considerably increased probability of electric dipole transitions b ¹Σ _g ⁺ ?a ¹Δ_g, a ¹Δ_g?X³Σ _g ^? , b ¹Σ _g ⁺ ?X³Σ _g ^? induced in oxygen in the collision process.     

Sn-doped Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> cathode materials for lithium-ion batteries with enhanced electrochemical performance

Sn-doped Li-rich layered oxides of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ have been synthesized via a sol-gel method, and their microstructure and electrochemical performance have been studied. The addition of Sn⁴⁺ ions has no distinct influence on the crystal structure of the materials. After doped with an appropriate amount of Sn⁴⁺, the electrochemical performance of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ cathode materials is significantly enhanced. The optimal electrochemical performance is obtained at x = 0.01. The Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode delivers a high initial discharge capacity of 268.9 mAh g^?1 with an initial coulombic efficiency of 76.5% and a reversible capacity of 199.8 mAh g^?1 at 0.1 C with capacity retention of 75.2% after 100 cycles. In addition, the Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode exhibits the superior rate capability with discharge capacities of 239.8, 198.6, 164.4, 133.4, and 88.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively, which are much higher than those of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (196.2, 153.5, 117.5, 92.7, and 43.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively). The substitution of Sn⁴⁺ for Mn⁴⁺ enlarges the Li⁺ diffusion channels due to its larger ionic radius compared to Mn⁴⁺ and enhances the structural stability of Li-rich oxides, leading to the improved electrochemical performance in the Sn-doped Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials.     

Solvothermal Synthesis of a New Amine-Templated Vanadium Sulfate

A new organic-templated vanadium sulfate with formula [C₄H₁₂N₂][V^III (OH)(SO₄)₂] · H₂O 1 has been prepared under solvothermal conditions by using a mixture of glycol and water as solvent. The structure of this compound was characterized by IR, element analysis, TG and single crystal X-ray diffraction. The title compound crystallizes in the space group monoclinic, P2₁/c, a = 9.290(4) Å, b = 18.264(7) Å, c = 7.132(3) Å, β = 98.149(8)°,V = 1197.88 Å³, Z = 4. Structural analysis indicates that the title compound 1 possesses a 1D chain structure formed by VO₆ octahedra and SO₄ tetrahedra.     

The sol–gel chromium-modified V<Subscript>6</Subscript>O<Subscript>13</Subscript> as a cathodic material for lithium batteries

A new V₆O₁₃-based material has been synthesized via the sol–gel route. This sol–gel mixed oxide has been obtained from an appropriate heat treatment of the chromium-exchanged V₂O₅ xerogel performed under reducing atmosphere. This new compound, with the chemical formula Cr_0.36V₆O_13.50, exhibits a monoclinic structure (C2/m) with the following unit cell parameters, a=11.89 Å, b=3.68 Å, c=10.14 Å, β=101.18°. The electrochemical characterization of this compound has been performed using galvanostatic discharge–charge experiments in the potential range 4–1.5 V and completed by ac impedance spectroscopy measurements. It exhibits a specific capacity of about 370 mAh g^?1, which makes the compound Cr_0.36V₆O_13.50 the best one in the V₆O₁₃-based system: 85% of the initial capacity (315 mAh g^?1) after the 35th cycle is still available at C/25 without any polarization. From impedance spectroscopy, a high kinetics of Li transport (D _Li=1.8×10^?9 cm² s^?1) is found at mid-discharge.     

Co-precipitation spray-drying synthesis and electrochemical performance of stabilized LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials

In this paper, the LiNi_0.5Mn_1.5O₄ cathode materials of lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining process. The use of a spray-drying process to form particles, followed by a calcination treatment at the optimized temperature of 750 °C to produce spherical LiNi_0.5Mn_1.5O₄ particles with a cubic crystal structure, a specific surface area of 60.1 m² g^?1, a tap density of 1.15 g mL^?1, and a specific capacity of 132.9 mAh g^?1 at 0.1 C. The carbon nanofragment (CNF) additives, introduced into the spheres during the co-precipitation spray-drying period, greatly enhance the rate performance and cycling stability of LiNi_0.5Mn_1.5O₄. The sample with 1.0 wt.% CNF calcined at 750 °C exhibits a maximum capacity of 131.7 mAh g^?1 at 0.5 C and a capacity retention of 98.9% after 100 cycles. In addition, compared to the LiNi_0.5Mn_1.5O₄ material without CNF, the LiNi_0.5Mn_1.5O₄ with CNF demonstrates a high-rate capacity retention that increases from 69.1% to 95.2% after 100 cycles at 10 C, indicating an excellent rate capability. The usage of CNF and the synthetic method provide a promising choice for the synthesis of a stabilized LiNi_0.5Mn_1.5O₄ cathode material.

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Graphical Abstract Micro/nanostructured LiNi_0.5Mn_0.5O₄ cathode materials with enhanced electrochemical performances for high voltage lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining routine and using carbon nanofragments (CNFs) as additive.

     

Enhancement of vibrational level population of N2 and CO by photoelectron spectrometry

Photoionization of N₂ and CO by 736–744 Å doublet lines from a Ne I resonance discharge gives photoelectron spectra which show that all vibrational levels of N₂⁺, X²Σ_g⁺, and CO⁺, X²Σ⁺, situated below the ν′ = 0 level of the first excited ionic state, are populated. An autoionizing mechanism is proposed to interpret this result, as in the case of O₂ and NO.     

Synthesis and characterization of Sr<Subscript>0.75</Subscript>Y<Subscript>0.25</Subscript>Co<Subscript>0.9</Subscript>Ru<Subscript>0.1</Subscript>O<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript> perovskite as a solid oxide fuel cell cathode material

The oxygen-deficient Sr_0.75Y_0.25Co_0.9Ru_0.1O_3?δ (SYCR) cathode is systematically evaluated for the application of solid oxide fuel cells. X-ray diffraction analysis indicates that SYCR presents a tetragonal structure with space group of I4/mmm (139). In the measured high oxygen partial pressure (pO₂) region (0.01–0.21 atm), the conductivity increases with increasing pO₂ because of the oxygen vacancy annihilation and hole creation, relating to a general p-type semiconducting mechanism. To get an insight into the rate-limiting step of SYCR cathode, behaviors of individual polarization resistance (R ₁ and R ₂) are investigated in different pO₂. The obtained fitting results reveal that R ₁ is nearly independent on the pO₂, while R ₂ presents a (pO₂)^?0.5 dependence. At 800 °C, SYCR cathode exhibits an R _p value of 0.14 Ω cm², moreover, when using the wet hydrogen (～ 3% H₂O) as fuel and ambient air as oxidant, the maximum power density of single cell Ni-YSZ (yttria-stabilized zirconia)|YSZ|SYCR reaches 452.9 W cm^?2.     

Synthesis of high-energy-density LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode through surficial Nb doping for lithium-ion batteries

LiMn₂O₄ is one of the most promising cathode materials due to its high abundance and low cost. However, the practical application of LiMn₂O₄ is greatly limited owing to its low volumetric energy density. Therefore, increasing its energy density is an urgent problem to be resolved. Herein, using the simple and mass production preferred solid-state reaction, surficial Nb-doped LiMn₂O₄ composed of the truncated octahedral or spherical-like primary particles are successfully synthesized. Auger electron spectroscopy (AES) and X-ray diffraction (XRD) characterizations confirm that most of Nb⁵⁺ enrich in the surficial layer of the particles to form a LiMn_2-xNb_xO₄ phase. This kind of doping can increase the specific discharge capacity of LiMn₂O₄ materials. Contrast with the pristine LiMn₂O₄, the discharge capacity of LiMn_1.99Nb_0.01O₄-based 18650R-type battery increases from 1497 to 1705 mAh with the volumetric energy density increasing by ~?13.9%, benefiting from the joint increments of the specific discharge capacity from 119.5 to 123.7 mAh g^?1 and the compacted density from 2.81 to 3.10 g cm^?3. Furthermore, the capacity retention after 500 cycles at 1 C (1500 mA) is also improved by 17.1%.

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Graphical abstract ?

     

Adiabatic channel study of the capture of nitrogen and oxygen molecules by an ion: effect of nuclear symmetry and spin-spin interaction

Within the adiabatic channel treatment of ionmolecule capture we have calculated the low temperature capture rate constants of N₂(¹Σ _g ⁺ ) and O₂(³Σ _g ^? )in collisions with positive and negative ions. In both cases, the charge-quadrupole and the anisotropic charge-induced dipole interactions produce noticeable deviations from the Langevin rate constant. The rate constants calculated with account for the anisotropic interaction, in addition, are substantially affected by nuclear symmetry; in the case of O₂(³Σ _g ^? ), the fine-structure spin-spin interaction strongly manifests itself in the rate constants.     

Generation of high O2 (a1Δg) concentrations in O2/H2 mixtures

The effect of hydrogen on the concentration of singlet oxygen in the a¹Δ_g and b¹Σ states, generated from a microwave discharge in O₂ and in an O₂/Ar mixture, was studied in flow reactors. The addition of hydrogen, in a range of 0.01–1 of concentration of the O₂, increased the yields of singlet oxygen by factor of 5–20. In addition to the higher O₂ (a and b) concentrations, the addition of hydrogen removed the usual NO₂ fluorescence, making observation of the O₂(b → X) transition at 762 nm much easier in the flow reactor. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 12–17, 2006     

Metal-free boron-doped carbon microspheres as excellent cathode catalyst for rechargeable Li–O<Subscript>2</Subscript> battery

Rechargeable Li–O₂ batteries are attracting more and more interest due to their high energy density. Meanwhile, the replacement of high-cost and scarce precious-metal catalysts has attracted more and more attention. Currently, many academic researchers have paid attention to find highly efficient metal-free catalysts as air cathode material. Herein, the boron-doped carbon microspheres (B-CMs) were prepared through a novel and facile static calcination method and showed high electrocatalytic activity as a cathode material. The battery with a B-CM cathode delivered a high initial discharge capacity of 13,757.2 mAh g^?1 and outstanding coulombic efficiency of 90.1 % at 100 mA g^?1. In addition, stable cyclability (151 cycles with stable discharge voltage of ~2.60 V with a cutoff capacity of 1000 mAh g^?1 at 200 mA g^?1) has been exhibited. These performances are due to three main points: boron carbide compound changed the surface area of the CMs and formed the mesopore architectures as well as the large surface area of 683.738 m² g^?1; the reduce of boron atom can slow down the oxidation of the CMs during the cyclings; and finally, the electron-deficient boron atom introduction greatly facilitated Li⁺ diffusion and electrolyte immersion and enhanced the oxygen reduction and evolution reaction kinetics.     

1D Chain-Like Architecture in Anderson Heteropolymolybdate {[Eu(H2O)6]2(TeMo6O24)}·6H2O: Synthesis and Characterization

A new Anderson-based heteropolymolybdate {[Eu(H₂O)₆]₂(TeMo₆O₂₄)}·6H₂O (1) has been hydrothermally synthesized and characterized by elemental analyses, IR, thermal stability analysis, XRD and single crystal X-ray diffraction. Compound 1 crystallizes in the triclinic system, space group P-1, a = 9.4023(6) Å, b = 10.2530(7) Å, c = 10.6525(10) Å, α = 101.583(7)º, β = 108.024(7)º, γ = 107.150(6)º, V = 883.60(12) ų, Z = 1, R₁ = 0.0338, wR₂ = 0.0849. Compound 1 exhibits 1D chain-like structure formed by the alternative connection between Anderson type polyoxoanions [TeMo₆O₂₄]^6? and Eu³⁺ along a-axis. Compound 1 displays good fluorescent emission of the Eu³⁺ ion at room temperature.     

Hydrothermal Synthesis and Characterization of a New Arsenic–Vanadium Compound with a β-[As<Subscript>8</Subscript>V<Subscript>14</Subscript>O<Subscript>42</Subscript>(SO<Subscript>4</Subscript>)]<Superscript>6−</Superscript> anion

A new arsenic vanadium compound (NH₄)₂[N(CH₃)₄]₄[β-As₈V₁₄O₄₂(SO₄)] 1 has been synthesized under hydrothermal conditions and characterized by single crystal X-ray diffraction, IR spectrum, elemental analysis and thermogravimetic (TG) analysis. Compound 1 crystallizes in monoclinic system with space group P2(1)/c, a = 11.4631(5) Å, b = 11.3539(5) Å, c = 24.6265(10) Å, β = 93.6620(10)°, V = 3198.6(2) ų, Z = 2, R1 = 0.0421 and wR2 = 0.1044. The molecule structural analysis reveals that compound 1 has a β-[As₈V₁₄O₄₂(SO₄)]^6? arsenic–vanadium cluster anion.     

Activated hierarchical porous carbon@π-conjugated polymer composite as cathode for high-performance lithium storage

Organic compounds become promising candidates for cathodes of rechargeable lithium battery (RLB) due to the high theoretical capacity and improved safety. However, they exhibit low conductivity and easy dissolution in electrolyte, which leads to the low utilization of active materials and poor cycling stability of RLBs. Here, we synthesize a novel composite of activated hierarchical porous carbon supporting poly(1,5-diamino-anthraquinone) (aHPC@PDAA), using Ce(SO₄)₂ as oxidant and naphthalenesulfonic acid (NSA) as soft template for PDAA. The as-synthesized composite exhibits uniformly nanoporous structure with nano-sized PDAA particles distributed homogenously inside and outside of pores. The aHPC@PDAA cathode for RLBs achieves high electrochemical performance with a discharge capacity as much as 250 mAh g^?1 at the current density of 100 mA g^?1, which still maintains 176 mAh g^?1 after 2000 charging-discharging cycles.