A Superior Na3 V2 (PO4 )3 -Based Nanocomposite Enhanced by Both N-Doped Coating Carbon and Graphene as the Cathode for Sodium-Ion Batteries.

A superior Na3 V2 (PO4 )3 -based nanocomposite (NVP/C/rGO) has been successfully developed by a facile carbothermal reduction method using one most-common chelator, disodium ethylenediamintetraacetate [Na2 (C10 H16 N2 O8 )], as both sodium and nitrogen-doped carbon sources for the first time. 2D-reduced graphene oxide (rGO) nanosheets are also employed as highly conductive additives to facilitate the electrical conductivity and limit the growth of NVP nanoparticles. When used as the cathode material for sodium-ion batteries, the NVP/C/rGO nanocomposite exhibits the highest discharge capacity, the best high-rate capabilities and prolonged cycling life compared to the pristine NVP and single-carbon-modified NVP/C. Specifically, the 0.1 C discharge capacity delivered by the NVP/C/rGO is 116.8 mAh g(-1) , which is obviously higher than 106 and 112.3 mAh g(-1) for the NVP/C and pristine NVP respectively; it can still deliver a specific capacity of about 80 mAh g(-1) even at a high rate up to 30 C; and its capacity decay is as low as 0.0355 % per cycle when cycled at 0.2 C. Furthermore, the electrochemical impedance spectroscopy was also implemented to compare the electrode kinetics of all three NVP-based cathodes including the apparent Na diffusion coefficients and charge-transfer resistances.

Theoretical Studies of the Reactions CFx H3-x COOR+Cl and CF3 COOCH3 +OH.

The mechanism and kinetics of the reactions of CF(3)COOCH(2)CH(3), CF(2)HCOOCH(3), and CF(3)COOCH(3) with Cl and OH radicals are studied using the B3LYP, MP2, BHandHLYP, and M06-2X methods with the 6-311G(d,p) basis set. The study is further refined by using the CCSD(T) and QCISD(T)/6-311++G(d,p) methods. Seven hydrogen-abstraction channels are found. All the rate constants, computed by a dual-level direct method with a small-curvature tunneling correction, are in good agreement with the experimental data. The tunneling effect is found to be important for the calculated rate constants in the low-temperature range. For the reaction of CF(3)COOCH(2)CH(3) +Cl, H-abstraction from the CH(2) group is found to be the dominant reaction channel. The standard enthalpies of formation for the species are also calculated. The Arrhenius expressions are fitted within 200-1000 K as kT(1) =8.4×10(-20) T (2.63) exp(381.28/T), kT(2) =2.95×10(-21) T (3.13) exp(-103.21/T), kT(3) =1.25×10(-23) T (3.37) exp(791.98/T), and kT(4) =4.53×10(-22) T (3.07) exp(465.00/T).

Theoretical study on the reactions of (CF3)2CFOCH3 + OH/Cl and reaction of (CF3)2CFOCHO with Cl atom.

Reactions of (CF3)2CFOCH3 and (CF3)2CFOCHO with hydroxyl radical and chlorine atom are studied at the B3LYP and BHandHLYP/6-311+G(d,p) levels along with the geometries and frequencies of all stationary points. This study is further refined by CCSD(T) and QCISD(T)/6-311+G(d,p) methods in the minimum energy paths. For the reaction (CF3)2CFOCH3 + OH, two hydrogen abstraction channels are found. The total rate constants for the reactions (CF3)2CFOCH3 + OH/Cl and (CF3)2CFOCHO + Cl are followed by means of the canonical variational transition state with the small-curvature tunneling correction. The comparison between the hydrogen abstraction rate constants by hydroxyl and chlorine atom is discussed. Calculated rate constants are in reasonable agreement with the available experiment data. The standard enthalpies of formation for the reactants, (CF3)2CFOCH3 and (CF3)2CFOCHO, and two products, (CF3)2CFOCH2 and (CF3)2CFOCO, are evaluated by a series of isodesmic reactions. The Arrhenius expressions for the title reactions are given as follows: k1= 1.08 × 10(-22) T(3.38) exp(-213.31/T), k2= 3.55 × 10(-22) T(3.61) exp(-240.26/T), and k3= 3.00 × 10 (-19) T(2.58) exp(-1294.34/T) cm(3) molecule(-1) s(-1).

Theoretical study on the gas phase reaction of propargyl alcohol with hydroxyl radical.

The reaction of propargyl alcohol with hydroxyl radical has been studied extensively at CCSD(T)/aug-cc-pVTZ//MP2/cc-pVTZ level. This is the first time to gain a conclusive insight into the reaction mechanism and kinetics for this important reaction in detail. Two reaction mechanisms were revealed, namely addition/elimination and hydrogen abstraction mechanism. The reaction mechanism confirms that OH addition to C≡C triple bond forms the chemically activated adducts, IM1 (·CHCOHCH2OH) and IM2 (CHOH·CCH2OH), and the hydrogen abstraction pathways (-CH2OH bonded to the carbon atom and alcohol hydrogen) may occur via low barriers. Harmonic model of Rice-Ramsperger-Kassel-Marcus theory and variational transition state theory are used to calculate the overall and individual rate constants over a wide range of temperatures and pressures. The calculated rate constants are in good agreement with the experimental data. At atmospheric pressure with Ar as bath gas, IM1 (·CHCOHCH2OH) and IM2 (CHOH·CCH2OH) formed by collisional stabilization are dominant in the low temperature range. The production of CHCCHOH + H2O via hydrogen abstraction becomes dominate at higher temperature. The fraction of IM3 (CH2COHCH2·O) is very significant over the moderate temperature range.

Li3PO4-coated LiNi0.5Mn1.5O4: a stable high-voltage cathode material for lithium-ion batteries.

LiNi0.5Mn1.5O4 is regarded as a promising cathode material to increase the energy density of lithium-ion batteries due to the high discharge voltage (ca. 4.7 V). However, the interface between the LiNi0.5Mn1.5O4 cathode and the electrolyte is a great concern because of the decomposition of the electrolyte on the cathode surface at high operational potentials. To build a stable and functional protecting layer of Li3PO4 on LiNi0.5Mn1.5O4 to avoid direct contact between the active materials and the electrolyte is the emphasis of this study. Li3PO4-coated LiNi0.5Mn1.5O4 is prepared by a solid-state reaction and noncoated LiNi0.5Mn1.5O4 is prepared by the same method as a control. The materials are fully characterized by XRD, FT-IR, and high-resolution TEM. TEM shows that the Li3PO4 layer (<6 nm) is successfully coated on the LiNi0.5Mn1.5O4 primary particles. XRD and FT-IR reveal that the synthesized Li3PO4-coated LiNi0.5Mn1.5O4 has a cubic spinel structure with a space group of Fd3m, whereas noncoated LiNi0.5Mn1.5O4 shows a cubic spinel structure with a space group of P4(3)32. The electrochemical performance of the prepared materials is characterized in half and full cells. Li3PO4-coated LiNi0.5Mn1.5O4 shows dramatically enhanced cycling performance compared with noncoated LiNi0.5Mn1.5O4.

Morphology and surface properties of LiVOPO4: a first principles study.

First principles calculations were used to investigate the surface energies, equilibrium morphology, surface redox potentials, and surface electrical conductivity of LiVOPO4. Relatively low-energy surfaces are found in the (100), (010), (001), (011), (111), and (201) orientations of the orthorhombic structure. Thermodynamic equilibrium shape of the LiVOPO4 crystal is built with the calculated surface energies through a Wulff construction. The (001) and (111) orientations are the dominating surfaces in the Wulff shape. Similar calculations for VOPO4 display a larger decrease in surface energies for the (100) surface rather than those in the other surfaces. It suggests that the Wulff shape of LiVOPO4 is closely related to the chemical environment around. Surfaces (100), (010) and (201) present lower Li surface redox potentials in comparison with the bulk material. Therefore, the Li migration rate on surfaces could be effectively increased by maximizing the exposure of these low redox potential surfaces. In addition, lower surface band gaps are found in all orientations compared to the bulk one, which indicates that electrical conductivity can be improved significantly by enlarging surfaces with relatively low band gaps in the particle. Therefore, synthesizing (201) and (100) nanosheets will greatly improve the electrochemical properties of the material.

Theoretical study on the gas phase reaction of allyl chloride with hydroxyl radical.

The reaction of allyl chloride with the hydroxyl radical has been investigated on a sound theoretical basis. This is the first time to gain a conclusive insight into the reaction mechanism and kinetics for important pathways in detail. The reaction mechanism confirms that OH addition to the C=C double bond forms the chemically activated adducts, IM1 (CH2CHOHCH2Cl) and IM2 (CH2OHCHCH2Cl) via low barriers, and direct H-abstraction paths may also occur. Variational transition state model and multichannel RRKM theory are employed to calculate the temperature-, pressure-dependent rate constants. The calculated rate constants are in good agreement with the experimental data. At 100 Torr with He as bath gas, IM6 formed by collisional stabilization is the major products in the temperature range 200-600 K; the production of CH2CHCHCl via hydrogen abstractions becomes dominant at high temperatures (600-3000 K).

Atmospheric chemistry of CF3O2: a theoretical study on mechanisms and pathways of the CF3O2 + IO reaction.

The mechanisms and reaction pathways for the CF3O2 + IO reaction have been investigated by quantum chemistry methods. It has been found that the title reaction takes place on both the singlet and triplet potential energy surfaces (PES). On the singlet PES, the most important products include CF3OOOI, CF3OOIO, CF3OIO2, and CF2O + FIO2, while other products such as CF2O + FOIO, CF2O + FOOI, CF3OOI + O((3)P), CF3OI + O2 ((1)Δ and (3)Σ), and CF3O + OIO are negligible due to high barriers or unstable formations. On the triplet PES, CF3O + OIO is the dominant product with a lower barrier. As for FIO2 and it isomers, the most stable one is FIO2. TDDFT (Time Dependent Density Functional Theory) calculation indicates that CF3OOOI, CF3OOIO and CF3OIO2 undergo photolysis easily under sunlight. Moreover, a minor contribution relative to hydrogen is found in the CX3O2 + IO (X = H and F) reactions.

Theoretical study on the gas phase reaction of allyl alcohol with hydroxyl radical.

The complex potential energy surface of allyl alcohol (CH2CHCH2OH) with hydroxyl radical (OH) has been investigated at the G3(MP2)//MP2/6-311++G(d,p) level. On the surface, two kinds of pathways are revealed, namely, direct hydrogen abstraction and addition/elimination. Rice-Ramsperger-Kassel-Marcus theory and transition state theory are carried out to calculate the total and individual rate constants over a wide temperature and pressure region with tunneling correction. It is predicted that CH2CHOHCH2OH (IM1) formed by collisional stabilization is dominate in the temperature range (200-440 K) at atmospheric pressure with N2 (200-315 K at 10 Torr Ar and 100 Torr He). The production of CH2CHCHOH + H2O via direct hydrogen abstraction becomes dominate at higher temperature. The kinetic isotope effect (KIE) has also been calculated for the title reaction. Moreover, the calculated rate constants and KIE are in good agreement with the experimental data.

Selected-control synthesis of monodisperse Fe3O4@C core-shell spheres, chains, and rings as high-performance anode materials for lithium-ion batteries.

A method is reported for the first time for the selected-control, large-scale synthesis of monodispersed Fe(3)O(4)@C core-shell spheres, chains, and rings with tunable magnetic properties based on structural evolution from eccentric Fe(2)O(3)@poly(acrylic acid) core-shell nanoparticles. The Fe(3)O(4)@C core-shell spheres, chains, and rings were investigated as anode materials for lithium-ion batteries. Furthermore, a possible formation mechanism of Fe(3)O(4)@C core-shell chains and rings has also been proposed.

Electronic structures and optical properties of the IPR-violating C60X8 (X = H, F, and Cl) fullerene compounds: a computational study.

Stimulated by the preparation and characterization of the isolated pentagon rule (IPR) violating chlorofullerene: C(60)Cl(8) (Nat. Mater. 2008, 7, 790-794), we have performed a systematic investigation on the structural stabilities, electronic and optical properties of the IPR-violating C(60)X(8) (X = H, F, and Cl) fullerene compounds via density functional theory. The large energy gaps between the highest occupied and the lowest unoccupied molecular orbitals provide a clear indication of high chemical stabilities of C(60)X(8) derivatives, and moreover, the C(60)X(8) molecules present great aromatic character with the negative nucleus independent chemical shift values. In the addition reactions of C(60) (C(2v)) + 4X(2) → C(60)X(8), a series of exothermic processes are involved, with high reaction energies ranging from -71.97 to -233.16 kcal mol(-1). An investigation on the electronic property shows that C(60)F(8) and C(60)Cl(8) could be excellent electron acceptors as a consequence of large vertical electron affinities. The density of state analysis suggests that the frontier molecular orbitals of C(60)X(8) are mainly from the carbon orbitals of two separate annulene subunits, and the influence from X atoms is secondary. In addition, the ultraviolet-visible spectra and second-order hyperpolarizabilities of C(60)X(8) are calculated by means of time-dependent density functional theory and a finite field approach, respectively. Both the average static linear polarizability <α> and second-order hyperpolarizability <γ> of C(60)X(8) increase greatly compared to those of C(60).

Theoretical studies on the mechanisms and dynamics of OH radical with (CH3)3COOH and (CH3)2CHOOH.

A dual-level direct dynamic method is employed to study the reaction mechanism of hydroxyl radical with (CH(3))(3)COOH and (CH(3))(2)CHOOH. Eight hydrogen abstraction channels are found for title reactions. The energy paths are optimized at the BH&H-HLYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies method at the CCSD(T) and QCISD(T) theories. Rate coefficients for the reactions of the OH with (CH(3))(3)COOH/(CH(3))(2)CHOOH are computed by the canonical variational transition-state theory with the small-curvature tunneling correction between 200 and 2000 K. The Arrhenius expressions k(1) (T) = 1.49 × 10(-26) T(4.71) exp(1981.92/T) and k(2) (T) = 1.58 × 10(-20) T(3.32) exp(210.59/T) over 200-2000 K are obtained.

Mechanistic and kinetic study of CF3CH═CH2 + OH reaction.

The potential energy surfaces of the CF(3)CH═CH(2) + OH reaction have been investigated at the BMC-CCSD level based on the geometric parameters optimized at the MP2/6-311++G(d,p) level. Various possible H (or F)-abstraction and addition/elimination pathways are considered. Temperature- and pressure-dependent rate constants have been determined using Rice-Ramsperger-Kassel-Marcus theory with tunneling correction. It is shown that IM1 (CF(3)CHCH(2)OH) and IM2 (CF(3)CHOHCH(2)) formed by collisional stabilization are major products at 100 Torr pressure of Ar and in the temperature range of T < 700 K (at P = 700 Torr with N(2) as bath gas, T ≤ 900 K), whereas CH(2)═CHOH and CF(3) produced by the addition/elimination pathway are the dominant end products at 700-2000 K. The production of CF(3)CHCH and CF(3)CCH(2) produced by hydrogen abstractions become important at T ≥ 2000 K. The calculated results are in good agreement with available experimental data. The present theoretical study is helpful for the understanding the characteristics of the reaction of CF(3)CH═CH(2) + OH.

Theoretical study on the kinetics of OH radical reactions with CH3OOH and CH3CH2OOH.

The mechanisms and kinetics studies of the OH radical with alkyl hydroperoxides CH(3)OOH and CH(3)CH(2)OOH reactions have been carried out theoretically. The geometries and frequencies of all the stationary points are calculated at the UBHandHLYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies method at the MC-QCISD level of theory. For two reactions, five H-abstraction channels are found and five products (CH(3)OO, CH(2)OOH, CH(3)CH(2)OO, CH(2)CH(2)OOH, and CH(3)CHOOH) are produced during the above processes. The rate constants for the CH(3)OOH/CH(3)CH(2)OOH + OH reactions are corrected by canonical variational transition state theory within 250-1500 K, and the small-curvature tunneling is included. The total rate constants are evaluated from the sum of the individual rate constants and the branching ratios are in good agreement with the experimental data. The Arrhenius expressions for the reactions are obtained.

Thermochemical stabilities, electronic structures, and optical properties of C56X10 (X = H, F, and Cl) fullerene compounds.

Stimulated by the recent isolation and characterization of C56Cl10 chlorofullerene (Tan et al., J Am Chem Soc 2008, 130, 15240), we perform a systematic study on the geometrical structures, thermochemistry, and electronic and optical properties of C56X10 (X = H, F, and Cl) on the basis of density functional theory (DFT). Compared with pristine C56, the equatorial carbon atoms in C56X10 are saturated by X atoms and change to sp³ hybridization to release the large local strains. The addition reactions C56 + 5X2 --> C56X10 are highly exothermic, and the optimal temperature for synthesizing C56X10 should be ranged between 500 and 1000 K. By combining 10 X atoms at the abutting pentagon vertexes and active sites, C56Cl10 molecules exhibit large energy gaps between the highest occupied and lowest unoccupied molecular orbitals (from 2.84 to 3.00 eV), showing high chemical stabilities. The C56F10 and C56Cl10 could be excellent electron acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities. The density of states is also calculated, which suggest that the frontier molecular orbitals of C56X10 are mainly from the carbon orbitals of two separate annulene subunits, and the contributions derived from X atoms are secondary. In addition, the ultraviolet-visible spectra and second-order hyperpolarizabilities of C56X10 are calculated by means of time-dependent DFT and finite field approach, respectively. Both the average static linear polarizability <α> and second-order hyperpolarizability <γ> of these compounds are larger than those of C60 due to lower symmetric structures and high delocalization of π electron density on the two separate annulene subunits.

Theoretical study on the gas phase reaction of acrylonitrile with a hydroxyl radical.

The mechanism and kinetics of the reaction of acrylonitrile (CH(2)=CHCN) with hydroxyl (OH) has been investigated theoretically. This reaction is revealed to be one of the most significant loss processes of acrylonitrile. BHandHLYP and M05-2X methods are employed to obtain initial geometries. The reaction mechanism conforms that OH addition to C[double bond, length as m-dash]C double bond or C atom of -CN group to form the chemically activated adducts, 1-IM1(HOCH(2)=CHCN), 2-IM1(CH(2)=HOCHCN), and 3-IM1(CH(2)=CHCOHN) via low barriers, and direct hydrogen abstraction paths may also occur. Temperature- and pressure-dependent rate constants have been evaluated using the Rice-Ramsperger-Kassel-Marcus theory. The calculated rate constants are in good agreement with the experimental data. At atmospheric pressure with N(2) as bath gas, 1-IM1(OHCH(2)=CHCN) formed by collisional stabilization is the major product in the temperature range of 200-1200 K. The production of CH(2)CCN and CHCHCN via hydrogen abstractions becomes dominant at high temperatures (1200-3000 K).

Theoretical and kinetic study of the H + C2H5CN reaction.

The reaction of H radical with C(2)H(5)CN has been studied using various quantum chemistry methods. The geometries were optimized at the B3LYP/6-311+G(d,p) and B3LYP/6-311++G(2d,2p) levels. The single-point energies were calculated using G3 and BMC-CCSD methods based on B3LYP/6-311++G(2d,2p) geometries. Four mechanisms were investigated, namely, hydrogen abstraction, C-addition/elimination, N-addition/elimination and substitution. The kinetics of this reaction were studied using the transition state theory and multichannel Rice-Ramsperger-Kassel-Marcus methodologies over a wide temperature range of 200-3000 K. The calculated results indicate that C-addition/elimination channel is the most feasible over the whole temperature range. The deactivation of initial adduct C(2)H(5)CHN is dominant at lower temperature with bath gas H(2) of 760 Torr; whereas C(2)H(5)+HCN is the dominant product at higher temperature. Our calculated rate constants are in good agreement with the available experimental data.

Mechanistic and kinetic investigations of N2H4 + OH reaction.

The reaction of N(2)H(4) with OH has been investigated by quantum chemical methods. The results show that hydrogen abstraction mechanism is more feasible than substitution mechanism thermodynamically. The calculated rate constants agree with the available experimental data. The calculated results show that the variational effect is small at lower temperature region, while it becomes significant at higher temperature region. On the other hand, the small-curvature tunneling effect may play an important role in the temperature range 220-3000 K. Moreover, the calculated rate constants show negative temperature dependence at the temperatures below 500 K, which is in accordance with Vaghjiani's report that slightly negative temperature dependence is found over the temperature range of 258-637 K. The mechanism of the major product (N(2)H(3)) with OH has also been investigated theoretically to understand the title reaction thoroughly.

Electronic structures and nonlinear optical properties of highly deformed halofullerenes C(3v) C60F18 and D(3d) C60Cl30.

Electronic structures and nonlinear optical properties of two highly deformed halofullerenes C(3v) C(60)F(18) and D(3d) C(60)Cl(30) have been systematically studied by means of density functional theory. The large energy gaps (3.62 and 2.61 eV) between the highest occupied and lowest unoccupied molecular orbitals (HOMOs and LUMOs) and the strong aromatic character (with nucleus-independent chemical shifts varying from -15.08 to -23.71 ppm) of C(60)F(18) and C(60)Cl(30) indicate their high stabilities. Further investigations of electronic property show that C(60)F(18) and C(60)Cl(30) could be excellent electron acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities. The density of states and frontier molecular orbitals are also calculated, which present that HOMOs and LUMOs are mainly distributed in the tortoise shell subunit of C(60)F(18) and the aromatic [18] trannulene ring of C(60)Cl(30), and the influence from halogen atoms is secondary. In addition, the static linear polarizability and second-order hyperpolarizability of C(60)F(18) and C(60)Cl(30) are calculated using finite-field approach. The values of and for C(60)F(18) and C(60)Cl(30) molecules are significantly larger than those of C(60) because of their lower symmetric structures and high delocalization of pi electrons.

Computational studies on the mechanism and kinetics of Cl reaction with C2H5I.

The dual-level direct kinetics method has been used to investigate the multichannel reactions of C(2)H(5)I + Cl. Three hydrogen abstraction channels and one displacement process are found for the title reaction. The calculation indicates that the hydrogen abstraction from -CH(2)- group is the dominant reaction channel, and the displacement process may be negligible because of the high barrier. The rate constants for individual reaction channels are calculated by the improved canonical variational transition-state theory with small-curvature tunneling correction over the temperature range of 220-1500 K. Our results show that the tunneling correction plays an important role in the rate constant calculation in the low-temperature range. Agreement between the calculated and experimental data available is good. The Arrhenius expression k(T) = 2.33 x 10(-16) T(1.83) exp(-185.01/T) over a wide temperature range is obtained. Furthermore, the kinetic isotope effects for the reaction C(2)H(5)I + Cl are estimated so as to provide theoretical estimation for future laboratory investigation.