Co-reporter:Jin Chong, Jingping Zhang, Haiming Xie, Xiangyun Song, Gao Liu, Vincent Battaglia, Shidi Xun and Rongsun Wang
RSC Advances 2016 vol. 6(Issue 23) pp:19245-19251
Publication Date(Web):01 Feb 2016
DOI:10.1039/C6RA00119J
LiPO3, one of the compounds from the Li2O–P2O5 binary phase diagram, is successfully coated on LiNi0.5Mn1.5O4 particles as a bifunctional layer with respect to its good ionic conductivity and chemical passivation properties. The coating layer with a thickness of 1 nm is identified by X-ray diffraction (XRD) and high resolution transition electron microscopy (TEM). Fourier transform-infrared spectrometer (FT-IR) and Raman spectra reveal that LiPO3 coated LiNi0.5Mn1.5O4 (LiPO3/LiNi0.5Mn1.5O4) possesses a cubic spinel structure with a space group of Fdm. The electrochemical properties of synthesized materials are evaluated in both Li ion half cells and full cells. LiPO3/LiNi0.5Mn1.5O4 exhibits significantly enhanced rate performance and superior cyclability compared with non-coated LiNi0.5Mn1.5O4. Impedance analysis indicates that the LiPO3 coating dramatically reduces the LiPO3/LiNi0.5Mn1.5O4 cell impedance, especially the resistances of the lithium ion migration compared with non-coated LiNi0.5Mn1.5O4. In addition, the LiPO3 coating can effectively act as a passivation layer to minimize electrolyte–electrode interface side reactions and thus improve the long-term cyclability.
Co-reporter:Dai-Huo Liu, Hong-Yan Lü, Xing-Long Wu, Bao-Hua Hou, Fang Wan, Sheng-Da Bao, Qingyu Yan, Hai-Ming Xie and Rong-Shun Wang
Journal of Materials Chemistry A 2015 vol. 3(Issue 39) pp:19738-19746
Publication Date(Web):15 Jul 2015
DOI:10.1039/C5TA03556B
Among the transition metal oxides as anode materials for lithium ion batteries (LIBs), the MnO material should be the most promising one due to its many merits mainly relatively low voltage hysteresis. However, it still suffers from inferior rate capabilities and poor cycle life arising from kinetic limitations, drastic volume changes and severe agglomeration of active MnO particulates during cycling. In this paper, by integrating the typical strategies of improving the electrochemical properties of transition metal oxides, we had rationally designed and successfully prepared one superior MnO-based nanohybrid (MnO@C/RGO), in which carbon-coated MnO nanoparticles (MnO@C NPs) were electrically connected by three-dimensional conductive networks composed of flexible graphene nanosheets. Electrochemical tests demonstrated that, the MnO@C/RGO nanohybrid not only showed the best Li storage performance in comparison with the commercial MnO material, MnO@C NPs and carbon nanotube enhanced MnO@C NPs, but also exhibited much improved electrochemical properties compared with most of the previously reported MnO-based materials. The superior electrochemical properties of the MnO@C/RGO nanohybrid included a high specific capacity (up to 847 mA h g−1 at 80 mA g−1), excellent high-rate capabilities (for example, delivering 451 mA h g−1 at a very high current density of 7.6 A g−1) and long cycle life (800 cycles without capacity decay). More importantly, for the first time, we had achieved the discharging/charging of MnO-based materials without capacity increase even after 500 cycles by adjusting the voltage range, making the MnO@C/RGO nanohybrid more possible to be a really practical anode material for LIBs.
Co-reporter:Shu-Wen Kang, Hai-Ming Xie, Weimin Zhang, Jing-Ping Zhang, Zifeng Ma, Rong-Shun Wang, Xing-Long Wu
Electrochimica Acta 2015 Volume 176() pp:604-609
Publication Date(Web):10 September 2015
DOI:10.1016/j.electacta.2015.06.107
•A facile and mass-producible strategy was developed to modify the surface of Cu foils with carbon.•The modified carbon is robust and strong.•Overall performances of lithium ion batteries were improved by the surface carbon modification on Cu current collector.•Full-cell systems were used to evaluate the effects of Cu surface modification.We have developed a facile and mass-producible strategy named electric discharge method to successfully improve the surface properties of Cu foils with rough carbon layer. Electrochemical tests in half-cells demonstrate that the coated carbon layer can significantly reduce the polarization resistance and enhance the reversible capacity of graphite anode when utilizing the Cu foils as current collector for lithium ion batteries. More importantly, the developed carbon coated Cu anode current collector can also improve the overall performances of LiFePO4 full cells in terms of enhanced rate capability (from 887.9 to 946.3 mAh at 4C rate), reduced polarization voltage (11.7 mV lower at 4C rate), longer cycle life (about 650 increased cycles if taking 80 % capacity retention as the end of cycle life when used at 1 C rate) as well as improved low-temperature performance (capacity retention: 42.87% vs. 38.85% at -20 °C).
Co-reporter:Wei Li, Hong-Yan Lü, Xing-Long Wu, Hongyu Guan, Ying-Ying Wang, Fang Wan, Guang Wang, Li-Qun Yan, Hai-Ming Xie and Rong-Shun Wang
RSC Advances 2015 vol. 5(Issue 17) pp:12583-12591
Publication Date(Web):05 Jan 2015
DOI:10.1039/C4RA12383B
Graphene material prepared by reducing graphene oxide (GO, prepared by the modified Hummers method) has been considered as one of the most promising candidates for electrode materials for supercapacitors due to its mass producibility, high electrical conductivity, large specific surface area, and superior mechanical strength. However, it usually exhibits an unfavorable cycling performance, mainly large capacitance fading in the initial thousands of cycles, as shown but not discussed in some previous reports. In this paper, we not only find a similar phenomenon to a commercial graphene material, but also develop a very simple method to successfully enhance its electrochemical properties in terms of cycle life as well as high-rate performance, leakage current and alternating current impedance. For example, the relatively low capacitance retention of about 89.9% at the initial 1000th cycle was increased up to 99.7% after improvement, the capacitance retention was raised to 73% from 43% at a scan rate of 100 mV s−1 in cyclic voltammetry, and leakage current density was significantly more than halved (from 2.42 mA g−1 to 1.01 mA g−1). Additionally, the reasons for the improvement are also disclosed by analyzing the characterization results of X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. It is found that the optimization of the functional groups of doped nitrogen and oxygen atoms may contribute to the improvement of cycle life and decrease of leakage current density, and the enhanced rate performance can be attributed to the increase of electrical conductivity.
Co-reporter:Haijie Shi, Fengdi Wang, Wei Chen, Shuwei Tang, Wanqiao Zhang, Wenliang Li, Hao Sun, Jingping Zhang, Rongshun Wang
Journal of Molecular Graphics and Modelling 2015 Volume 59() pp:31-39
Publication Date(Web):June 2015
DOI:10.1016/j.jmgm.2015.03.004
•Homodimer of DeAPb has more stability than other dimers in various conditions.•Electron donating substituents can provide favorable free energies of dimerization.•The dimerization can be favored in weakly polar solvents.•Electron transfers from acceptor to donor owing to hyperconjugative interactions.•UV absorption spectra show evident difference of λmax between monomers and dimers.The heterocyclic urea of deazapterin (DeAPa) and its protomeric conformers (b, c) with different substituents are selected as the building block for a series of dimers in different configurations. The stabilities of all dimers in various conditions have been investigated by density functional theory. Homodimer of b has more stability than other dimers. Topological analyses certify the coexistence of intermolecular with intramolecular H-bonds. Investigations into frequency demonstrate that all H-bonds show an evident red shift in their stretching vibrational frequencies. Electron donating substituents can provide favorable free energies of the dimer. Solvent effect computations suggest that the dimerization can be favored in weakly polar solvents, such as toluene and chloroform. UV–visible spectra exhibit obvious difference of maximum absorption wavelengths between monomers and dimers, thus may have potential applications for identifying intermolecular H-bonds and calculating association constant of DeAP equilibrium systems in experiments.Intermolecular and intramolecular H-bonds coexist in dimers based on DeAP. Electron donating substituents and weakly polar solvents can promote the dimerization. Electron transfers from lone pairs of electron of O/N atoms in acceptor to NH bonds in donor as a result of hyperconjugative interactions. UV–visible spectra exhibit obvious difference of maximum absorption wavelengths between monomers and dimers.
Co-reporter:Yuhan Li, Jingping Zhang, Fengmei Yang, Jing Liang, Hao Sun, Shuwei Tang and Rongshun Wang
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 44) pp:24604-24609
Publication Date(Web):14 Oct 2014
DOI:10.1039/C4CP03628J
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.
Co-reporter:Peng Mei, Xing-Long Wu, Haiming Xie, Liqun Sun, Yanping Zeng, Jingping Zhang, Linghua Tai, Xin Guo, Lina Cong, Shunchao Ma, Cen Yao and Rongshun Wang
RSC Advances 2014 vol. 4(Issue 49) pp:25494-25501
Publication Date(Web):15 May 2014
DOI:10.1039/C4RA02269F
Nowadays one of the principal challenges for the development of lithium-ion batteries (LIBs) is fulfilling the burgeoning demands for high energy and power density with long cycle life. Herein, we demonstrate a two-step route for synthesizing LiV3O8 nanorods with a confined preferential orientation by using VO2(B) nanosheets made in the laboratory as the precursor. The special structures of nanorods endow the LiV3O8 materials with markedly enhanced reversible capacities, high-rate capability and long-term cycling stability as cathodes for lithium storage. The results show that very desirable initial capacities of 161 and 158 mA h g−1 can be achieved for the LiV3O8 nanorods at extremely high rates of 2000 and 3000 mA g−1, with minimal capacity loss of 0.037% and 0.031% per cycle throughout 300 and 500 cycles, respectively. The energetically optimized electron conduction and lithium diffusion kinetics in the electrode process may shed light on the superior electrochemical properties of the LiV3O8 nanorods, primarily benefitting from the small particle size, large surface area and restricted preferential ordering along the (100) plane.
Co-reporter:Yunju Zhang, Kai Chao, Xiumei Pan, Jingping Zhang, Zhongmin Su, Rongshun Wang
Journal of Molecular Graphics and Modelling 2014 Volume 48() pp:18-27
Publication Date(Web):March 2014
DOI:10.1016/j.jmgm.2013.09.003
•Potential energy surface for the title reaction has been investigated theoretically.•Multichannel RRKM theory is employed to calculate the rate constants.•The predicted rate constants are in agreement with the available experimental values.Potential energy surface for the reaction of hydroxyl radical (OH) with 3-fluoropropene (CH2CHCH2F) has been studied to evaluate the reaction mechanisms, possible products and rate constants. It has been shown that the CH2CHCH2F with OH reaction takes place via a barrierless addition/elimination and hydrogen abstraction mechanism. It is revealed for the first time that the initial step for the barrierless additional process involves a pre-reactive loosely bound complex (CR1) that is 1.60 kcal/mol below the energy of the reactants. Subsequently, the reaction bifurcates into two different pathways to form IM1 (CH2CHOHCH2F) and IM2 (CH2OHCHCH2F), which can decompose or isomerize to various products via complicated mechanisms. Variational transition state model and multichannel RRKM theory are employed to calculate the temperature-, pressure-dependent rate constants and branching ratios. At atmospheric pressure with He as bath gas, IM1 formed by collisional stabilization is dominated at T ≤ 600 K; whereas the direct hydrogen abstraction leading to CH2CHCHF and H2O are the major products at temperatures between 600 and 3000 K, with estimated contribution of 72.9% at 1000 K. Furthermore, the predicted rate constants are in good agreement with the available experimental values.
Co-reporter:Jin Chong;Dr. Shidi Xun; Jingping Zhang;Xiangyun Song; Haiming Xie;Dr. Vincent Battaglia; Rongshun Wang
Chemistry - A European Journal 2014 Volume 20( Issue 24) pp:7479-7485
Publication Date(Web):
DOI:10.1002/chem.201304744
Abstract
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 Fdm, whereas noncoated LiNi0.5Mn1.5O4 shows a cubic spinel structure with a space group of P4332. 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.
Co-reporter:Shunchao Ma, Liqun Sun, Lina Cong, Xuguang Gao, Cen Yao, Xin Guo, Linghua Tai, Peng Mei, Yanping Zeng, Haiming Xie, and Rongshun Wang
The Journal of Physical Chemistry C 2013 Volume 117(Issue 49) pp:25890-25897
Publication Date(Web):November 22, 2013
DOI:10.1021/jp407576q
Multiporous MnCo2O4 microspheres are fabricated via the solvothermal method followed by pyrolysis of carbonate precursor to demonstrate excellent bifunctional catalytic activity toward both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Because of this multiporous structure, the resulting MnCo2O4 microspheres show an efficient electrocatalytic performance in LiTFSI/TEGDME electrolyte-based Li–O2 batteries. MnCo2O4 microspheres as the air cathode deliver better performance during the discharging and charging processes and good cycle stability compared with that of the Super P. This preliminary result manifests that multiporous MnCo2O4 microspheres are promising cathode catalysts for nonaqueous Li–O2 batteries.
Co-reporter:F. Wang, S. P. Neville, R. Wang, and G. A. Worth
The Journal of Physical Chemistry A 2013 Volume 117(Issue 32) pp:7298-7307
Publication Date(Web):May 30, 2013
DOI:10.1021/jp401116c
A model Hamiltonian based on the quadratic vibronic coupling model is developed to describe the photoinduced dynamics of aniline excited to the manifold of states comprising its first six singlet electronic states. The model Hamiltonian is parametrized by fitting to the results of extensive EOM-CCSD calculations and its validity tested through the calculation of the first two bands in the electronic absorption spectrum of aniline. It is found that two previously neglected 3p Rydberg states play an important role in the dynamics of aniline following excitation into the first two 1ππ* states. Assignments of the vibrational structure seen in the experimental spectrum is made, and the role played by the Herzberg–Teller effect in excitation to the first 1ππ* state is analyzed.
Co-reporter:MingJuan Li;LiQun Sun;Kai Sun;RongShun Wang;HaiMing Xie
Science China Chemistry 2013 Volume 56( Issue 5) pp:576-582
Publication Date(Web):2013 May
DOI:10.1007/s11426-012-4818-0
LiFePO4 cathode material is synthesized by a simple solid-state reaction method with FePO4·2H2O as iron source and citric acid as reductive agent and carbon source. This study examines the effects of different oxidation routes to prepare FePO4·2H2O on the electrochemical performance of as-synthesized LiFePO4. Iron phosphate was prepared by two routes from FeSO4·7H2O. One is the formation of Fe3(PO4)2 precipitate in the first step and subsequent oxidation to FePO4 precipitate. The other is the oxidation of ferrous to ferric ion firstly, and then to form FePO4 precipitate directly. The results indicate that substantial differences in the structure and electrochemical properties of LiFePO4 depend on the behavior of FePO4. Iron phosphate obtained through one step precipitation has a smaller particle size and more uniform particle distribution, which is demonstrated to be more applicable as the iron source to synthesize LiFePO4/C. As-prepared LiFePO4/C shows an excellent rate capability and cycle performance. The initial discharge capacities of 160.6 mAh/g and 107 mAh/g are achieved at 0.1 C and 10 C, respectively. The good capacity retention of 97% after 300 cycles is maintained at the rate of 5 C.
Co-reporter:Yunju Zhang, Kai Chao, Jingyu Sun, Zhongmin Su, Xiumei Pan, Jingping Zhang, and Rongshun Wang
The Journal of Physical Chemistry A 2013 Volume 117(Issue 30) pp:6629-6640
Publication Date(Web):July 18, 2013
DOI:10.1021/jp402142b
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.
Co-reporter:Jing Liu, Guiling Yang, Xianfa Zhang, Jiawei Wang, Rongshun Wang
Journal of Power Sources 2012 Volume 197() pp:253-259
Publication Date(Web):1 January 2012
DOI:10.1016/j.jpowsour.2011.09.028
For the first time, a LiFePO4/C core–shell nanocomposite has been synthesized using a nano-FePO4/polythiophene (PTh) as an iron source. With this method, the PTh is in situ polymerized to restrain the growth of FePO4 particles, and the typical size of FePO4/PTh particles is in the range of 20–50 nm. The optimized LiFePO4/C nanocomposite is synthesized at 750 °C using 40% citric acid. The prepared LiFePO4 particles show a typical size of 50–100 nm and they are fully coated by carbon of 2–4 nm thickness. The LiFePO4/C core–shell nanocomposite gives an improved high electronic conductivity and a good electrochemical behavior at high rates. Thus, this novel method is an effective and facile strategy to improve the rate performance of the LiFePO4 cathode.Graphical abstractHighlights► A LiFePO4/C core-shell nanocomposite is synthesized from a nano-FePO4/PTh composite. ► The typical size of the FePO4/PTh is in the range of 20-50 nm. ► The optimized LiFePO4/C shows a typical size of 50-100 nm. ► The fully coated carbon layer observed by HRTEM is of 2-4 nm thickness. ► The prepared LiFePO4/C core-shell nanocomposite shows a good rate performance.
Co-reporter:Yunju Zhang, Jingyu Sun, Kai Chao, Fang Wang, ShuWei Tang, Xiumei Pan, Jingping Zhang, Hao Sun, Rongshun Wang
Computational and Theoretical Chemistry 2012 Volume 981() pp:7-13
Publication Date(Web):1 February 2012
DOI:10.1016/j.comptc.2011.11.010
The complex potential energy surfaces for the reaction of atomic radical F with CH2CHCH2Cl (3-chloropropene) are explored at the CCSD(T)/cc-pVTZ//MP2(full)/6-311++G(d,p) level. There are various possible reaction pathways including the addition–elimination and H-abstraction reaction. Among them, the most feasible pathway should be to produce P1 (CH2CHCH2F + Cl), which is in good agreement with the experiment. Among the H-abstraction reactions, the most competitive pathway is the atomic radical F abstracting hydrogen atom from allylic group. Because all of the transition states and intermediates involved in the title reaction lie below the reactants, the F + CH2CHCH2Cl reaction is expected to be rapid. The present results could lead us to deeply understand the mechanism of the title reaction and may provide some useful information for future experimental investigation of the title reaction.Graphical abstractHighlights► The mechanism of the title reaction has been carried out at MP2 and CCSD(T) levels. ► Two kinds of hydrogen abstraction and addition/elimination channels were considered. ► The results are in good agreement with available experimental value.
Co-reporter:Mingjuan Li;Liqun Sun;Kai Sun;Shihua Yu
Journal of Solid State Electrochemistry 2012 Volume 16( Issue 11) pp:3581-3586
Publication Date(Web):2012 November
DOI:10.1007/s10008-012-1790-8
Nanoscale LiFePO4/C particles are synthesized using a combination of electrospinning and annealing. The important advantages of electrospinning technique are the production of separated nanofiber precursor, enabling the precursor particles arrangement to be changed, impeding the growth and agglomeration of the LiFePO4 particles during the heat treatment, and contributing to the formation of nanosized LiFePO4 particles. In this study, polyvinylpyrrolidone (PVP) is used as the fiber-forming agent in the electrospinning method, and also provides a reducing agent and carbon source. In situ carbon-coated LiFePO4 particles are obtained by the pyrolysis of PVP during the thermal treatment. The LiFePO4 particles are coated with and connected by interlaced carbons, and are uniformly distributed in the size range 50–80 nm. It is found that the as-prepared nanoscale LiFePO4/C composite has a desirable electrochemical performance. It has discharge capacities of 163.5 mA h g−1 and 110.7 mA h g−1 at rates of 0.1 C and 10 C, respectively. In addition, this cathode has excellent cyclability with a capacity loss of less than 3 % at 0.1 C and 5 % at 5 C after 500 cycles. An effective synthesis and processing method is presented for obtaining nanosized LiFePO4 with high electrochemical performance.
Co-reporter:Yunju Zhang, Jingyu Sun, Kai Chao, Hao Sun, Fang Wang, ShuWei Tang, Xiumei Pan, Jingping Zhang, and Rongshun Wang
The Journal of Physical Chemistry A 2012 Volume 116(Issue 12) pp:3172-3181
Publication Date(Web):March 2, 2012
DOI:10.1021/jp209960c
The potential energy surfaces of the CF3CH═CH2 + 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 (CF3CHCH2OH) and IM2 (CF3CHOHCH2) 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 N2 as bath gas, T ≤ 900 K), whereas CH2═CHOH and CF3 produced by the addition/elimination pathway are the dominant end products at 700–2000 K. The production of CF3CHCH and CF3CCH2 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 CF3CH═CH2 + OH.
Co-reporter:Li-Qun Sun, Ming-Juan Li, Kai Sun, Shi-Hua Yu, Rong-Shun Wang, and Hai-Ming Xie
The Journal of Physical Chemistry C 2012 Volume 116(Issue 28) pp:14772-14779
Publication Date(Web):June 18, 2012
DOI:10.1021/jp302265n
Black phosphorus (black P), which is a promising candidate as an anode material for lithium-ion batteries, was synthesized by a high-pressure and high-temperature (HPHT) method from white and red phosphorus. The study revealed the electrochemical activity of pure black P under different pressures and temperatures systematically. The sample shows higher crystallinity and purity by the HPHT method. Lithium-ion batteries containing black phosphorus as anode materials exhibited a high specific capacity and excellent cycling performance. Black phosphorus obtained from white phosphorus exhibited the highest first discharge and charge capacities of 2505 and 1354 mAh·g–1 at 4 GPa and 400 °C and that obtained from red phosphorus exhibited the highest first discharge and charge capacities of 2649 and 1425 mAh·g–1 at 4.5 GPa and 800 °C. Black P was characterized by X-ray diffraction, Raman microscopy, scanning electron microscopy, and high-resolution transmission electron microscopy.
Co-reporter:Zijia Yu, Xianfa Zhang, Guiling Yang, Jing Liu, Jiawei Wang, Rongshun Wang, Jingping Zhang
Electrochimica Acta 2011 Volume 56(Issue 24) pp:8611-8617
Publication Date(Web):1 October 2011
DOI:10.1016/j.electacta.2011.07.051
Li4Ti4.9V0.1O12 nanometric powders were synthesized via a facile solid-state reaction method under inert atmosphere. XRD analyses demonstrated that the V-ions successfully entered the structure of cubic spinel-type Li4Ti5O12 (LTO), reduced the lattice parameter and no impurities appeared. Compared with the pristine LTO, the electronic conductivity of Li4Ti4.9V0.1O12 powders is as high as 2.9 × 10−1 S cm−1, which should be attributed to the transformation of some Ti3+ from Ti4+ induced by the efficient V-ions doping and the deficient oxygen condition. Meanwhile, the results of XPS and EDS further proved the coexistence of V5+ and Ti3+ ions. This mixed Ti4+/Ti3+ ions can remarkably improve its cycle stability at high discharge–charge rates because of the enhancement of the electronic conductivity. The images of SEM showed that Li4Ti4.9V0.1O12 powders have smaller particles and narrower particle size distribution under 330 nm. And EIS indicates that Li4Ti4.9V0.1O12 has a faster lithium-ion diffusivity than LTO. Between 1.0 and 2.5 V, the electrochemical performance, especially at high rates, is excellent. The discharge capacities are as high as 166 mAh g−1 at 0.5C and 117.3 mAh g−1 at 5C. At the rate of 2C, it exhibits a long-term cyclability, retaining over 97.9% of its initial discharge capacity beyond 1713 cycles. These outstanding electrochemical performances should be ascribed to its nanometric particle size and high conductivity (both electron and lithium ion). Therefore, the as-prepared material is promising for such extensive applications as plug-in hybrid electric vehicles and electric vehicles.Highlights► Higher electronic conductivity of Li4Ti4.9V0.1O12 is 2.9 × 10−1 S cm−1. ► Smaller particles and narrower particle size distribution of Li4Ti4.9V0.1O12. ► XPS demonstrates the existence of Ti3+ and V5+ ions in Li4Ti4.9V0.1O12. ► Li4Ti4.9V0.1O12 has more excellent electrochemical performance.
Co-reporter:Jingyu Sun, Rongshun Wang and Baoshan Wang
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 37) pp:16585-16595
Publication Date(Web):17 Aug 2011
DOI:10.1039/C1CP20836E
The mechanism and kinetics of the reaction of acrylonitrile (CH2CHCN) 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 CC double bond or C atom of –CN group to form the chemically activated adducts, 1-IM1(HOCH2CHCN), 2-IM1(CH2HOCHCN), and 3-IM1(CH2CHCOHN) 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 N2 as bath gas, 1-IM1(OHCH2CHCN) formed by collisional stabilization is the major product in the temperature range of 200–1200 K. The production of CH2CCN and CHCHCNviahydrogen abstractions becomes dominant at high temperatures (1200–3000 K).
Co-reporter:Kui-Zhan Shao, Ya-Hui Zhao, Ya-Qian Lan, Xin-Long Wang, Zhong-Min Su and Rong-Shun Wang
CrystEngComm 2011 vol. 13(Issue 3) pp:889-896
Publication Date(Web):18 Oct 2010
DOI:10.1039/C0CE00042F
An investigation into the molecular tectonics of metal–organic frameworks (MOFs) is reported on the basis of N-donor ligand modulated polynuclear zinc clusters and different aromatic polycarboxylic ligands. A series of three-dimensional (3D) coordination frameworks, [Zn2(BDC)1.5(L)(OH)]·H2O (1), [Zn2(BOABA)(L)(OH)]·2H2O (2), [Zn2(BOABA)(L)(OH)]·4H2O (3), [Zn3(BTC)2(OH)]·0.25H2O·[N(C4H9)4] (4) and [Zn2(BTEC)0.5(L)(OH)2] (5), were synthesized by self-assembly of zinc ions with a new N-donor ligand 4,5-diazafluoren-9-oxime (L) and the aromatic polycarboxylic ligands 1,4-benzenedicarboxylic acid (H2BDC), 3,5-bis-oxyacetate-benzoic acid (H3BOABA), 1,3,5-benzenetricarboxylic acid (H3BTC), and 1,2,4,5-benzenetetracarboxylic acid (H4BTEC). Compound 1 exhibits a twofold interpenetrated α-polonium-type network based on tetranuclear Zn clusters as six-connected vertices and BDC ligands as linkers. Compound 2 also consists of tetranuclear units, it shows a (3,6)-connected rutile network, where tetranuclear zinc clusters act as six-connected nodes and BOABA ligands act as three-connected nodes. Compound 3 is an isomer of compound 2, due to the different configuration of tetranuclear zinc, it displays a novel (3,6)-connected network with a complex (4·62)2(42·69·84) topology. In 4, the connection between the trinuclear zinc clusters and the BTC ligands results in an infinite 3D (3,6)-connected network with point symbol (4·62)(63)(4·611·83). Compound 5 constitutes a lvt net, which is built from tetranuclear clusters and BTEC as four-connected nodes, respectively. The results indicate that various polynuclear zinc clusters are modulated by L ligands combining with Zn atoms via chelation or monodentate coordination, or acting as a structure-directing agent. Meanwhile, aromatic multicarboxylic acids also play important roles in the construction of the compounds with various structures.
Co-reporter:Yunju Zhang, Jingyu Sun, Kai Chao, Fang Wang, Hao Sun, ShuWei Tang, Xiumei Pan, Jingping Zhang, Rongshun Wang, Lihua Chen
Computational and Theoretical Chemistry 2011 Volume 965(Issue 1) pp:68-83
Publication Date(Web):April 2011
DOI:10.1016/j.comptc.2011.01.028
The detailed potential energy surface for the key atmospheric reaction of OH with CH2CHCH(OH)CH3 (3-buten-2-ol) has been investigated at the CCSD(T)/6-311++G(d,p)//MP2(full)/6-311++G(d,p) level. Various possible H-abstraction and addition–elimination pathways are identified. It is predicted that the formation of intermediates c1 (CH2CH(OH)CH(OH)CH3) in the addition process via pre-reactive complex a3 is more favorable than that of the H-abstraction reactions at low temperature. Starting from c1, the most feasible pathway is the formation of P7 (CH2CHOH(I) + CH3CHOH(I)) by directly CC bond rupture or formation of P14 (CH3CHO + CH3CHOH(I)) via isomerization/dissociation mechanisms, all of which have comparable contributions to the title reaction. P14 (CH3CHO + CH3CHOH(I)) are the dominate products. In the H-abstraction pathways, the dominant channel is the allylic H atom abstraction leading to P5 (CH2CHC(OH)CH3) + H2O, which may play an important role at higher temperature. The other pathways are less significant due to higher barrier height and unstable product. This calculation is useful to simulate to guide experimental investigations of the title reaction.
Co-reporter:Guiling Yang, Xianfa Zhang, Jing Liu, Xingguang He, Jiawei Wang, Haiming Xie, Rongshun Wang
Journal of Power Sources 2010 Volume 195(Issue 4) pp:1211-1215
Publication Date(Web):15 February 2010
DOI:10.1016/j.jpowsour.2009.08.060
LiFePO4/polyacenes (PAS) composite is synthesized by iron oxyhydroxide as a new raw material and phenol–formaldehyde resin as both reducing agent and carbon source. The mechanism of the reaction is outlined by the analysis of XRD, FTIR as well as TG/DSC. The results show that the formation of LiFePO4 is started at 300 °C, and above 550 °C, the product can be mainly ascribed to olivine LiFePO4. The electrochemical properties of the synthesized composites are investigated by charge–discharge tests. It is found that the prepared sample at 750 °C (S750) has a better electrochemical performance than samples prepared at other temperatures. A discharge capacity of 158 mAh g−1 is delivered at 0.2 C. Under high discharge rate of 10 C, a discharge capacity of 145 mAh g−1 and good capacity retention of 93% after 800 cycles are achieved. The morphology of S750 and PAS distribution in it are investigated by SEM and TEM.
Co-reporter:Jiawei Wang, Xianfa Zhang, Jing Liu, Guiling Yang, Yucui Ge, Zijia Yu, Rongshun Wang, Xiumei Pan
Electrochimica Acta 2010 Volume 55(Issue 22) pp:6879-6884
Publication Date(Web):1 September 2010
DOI:10.1016/j.electacta.2010.05.077
The Li3V2(PO4)3/C composite cathode material is synthesized via a simple carbothermal reduction reaction route using polyvinyl alcohol (PVA) as both reduction agent and carbon source. The XRD pattern shows that the as-prepared Li3V2(PO4)3/C composite has a monoclinic structure with space group P21/n. The result of XPS shows the oxidation state of V in the Li3V2(PO4)3/C composite is +3. The Raman spectrum reveals that the coating carbon has a good structure with a low ID/IG ratio. The high-quality carbon can not only enhance the electronic conductivity of the Li3V2(PO4)3/C composite but also prevent the growth of the particle size. The electrochemical performance, which is especially notable for its high-rate performance, is excellent. It delivers an initial discharge capacity of 105.3 mAh/g at 5 C, which is retained as high as 90% after 2000 cycles. No capacity loss can be observed up to 300 cycles under 20 C rate condition. Our experimental results suggest that this compound can be a candidate as cathode materials for the power batteries of hybrid electric vehicles (HEVs) and electric vehicles (EVs) in the future.
Co-reporter:Yucui Ge, Xuedong Yan, Jing Liu, Xianfa Zhang, Jiawei Wang, Xingguang He, Rongshun Wang, Haiming Xie
Electrochimica Acta 2010 Volume 55(Issue 20) pp:5886-5890
Publication Date(Web):1 August 2010
DOI:10.1016/j.electacta.2010.05.040
Both Ni doping and carbon coating are adopted to synthesize a nano-sized LiFePO4 cathode material through a simple solid-state reaction. It is found that the Ni2+ has been successfully doped into LiFePO4 without affecting the phospho-olivine structure from the XRD result. The images of SEM and TEM show that the size of particles is distributed in the range of 20–60 nm, and all the particles are coated with carbon completely. The results of XPS show the valence state of Fe and Ni in the LiFePO4. The electronic conductivity of the material is as high as 2.1 × 10−1 S cm−1, which should be ascribed to the coefficient of the conductive carbon network and Ni doping. As a cathode material for lithium-ion batteries, the Ni doped LiFePO4/C nanocomposite delivers a discharge capacity of 170 mAh g−1 at 0.2 C, approaching the theoretical value. Moreover, the material shows excellent high-rate charge and discharge capability and long-term cyclability. At the high rates of 10 and 15 C, this material exhibits high capacities of 150 and 130 mAh g−1, retaining 95% after 5500 cycles and 93% after 7200 cycles, respectively. Therefore, the as-prepared material is capable of such large-scale applications as electric vehicles and plug-in hybrid electric vehicles.
Co-reporter:Xianfa Zhang, Jing Liu, Haiying Yu, Guiling Yang, Jiawei Wang, Zijia Yu, Haiming Xie, Rongshun Wang
Electrochimica Acta 2010 Volume 55(Issue 7) pp:2414-2417
Publication Date(Web):28 February 2010
DOI:10.1016/j.electacta.2009.12.001
A simple and effective method, ethylene glycol-assisted co-precipitation method, has been employed to synthesize LiNi0.5Mn1.5O4 spinel. As a chelating agent, ethylene glycol can realize the homogenous distributions of metal ions at the atomic scale and prevent the growth of LiNi0.5Mn1.5O4 particles. XRD reveals that the prepared material is a pure-phase cubic spinel structure (Fd3m) without any impurities. SEM images show that it has an agglomerate structure with the primary particle size of less than 100 nm. Electrochemical tests demonstrate that the as-prepared LiNi0.5Mn1.5O4 possesses high capacity and excellent rate capability. At 0.1 C rate, it shows a discharge capacity of 137 mAh g−1 which is about 93.4% of the theoretical capacity (146.7 mAh g−1). At the high rate of 5 C, it can still deliver a discharge capacity of 117 mAh g−1 with excellent capacity retention rate of more than 95% after 50 cycles. These results show that the as-prepared LiNi0.5Mn1.5O4 is a promising cathode material for high power Li-ion batteries.
Co-reporter:Jing Liu, Fukuan Liu, Guiling Yang, Xianfa Zhang, Jiawei Wang, Rongshun Wang
Electrochimica Acta 2010 Volume 55(Issue 3) pp:1067-1071
Publication Date(Web):1 January 2010
DOI:10.1016/j.electacta.2009.09.056
A simple and effective method has been developed to synthesize a nano-sized LiFePO4/PAS (polyacenic semiconductor) composite. The LiFePO4 particles coated and connected by PAS are uniformly distributed in the range of 50–80 nm. The electronic conductivity of this material is as high as 1.2 × 10−1 S/cm due to the conductive network of PAS. In comparison with the micro-LiFePO4/PAS, the nano-LiFePO4/PAS exhibits much better rate performance. At the 12-min charge–discharge rate, the power and energy densities of the nano-LiFePO4/PAS are shown as 2063 W/kg and 412 Wh/kg, which are much higher than those of the micro-LiFePO4/PAS (1600 W/kg and 320 Wh/kg). It is especially notable that the nano-LiFePO4/PAS cathode without adding Super P shows similar electrochemical behaviors with the cathode adding Super P at all C-rates. Thus, such cathode without adding Super P will enlarge both the volume energy density and weight energy density of batteries. In addition, this cathode exhibits an excellent long-term cyclability, retaining over 95.4% of its original discharge capacity beyond 500 cycles at 0.2C rate. These favorable electrochemical performances should be attributed to its nanometric particle size and the high electronic conductivity.
Co-reporter:Jing-Dong Feng, Kui-Zhan Shao, Shu-Wei Tang, Rong-Shun Wang and Zhong-Min Su
CrystEngComm 2010 vol. 12(Issue 5) pp:1401-1403
Publication Date(Web):09 Apr 2010
DOI:10.1039/B923583C
The first ionothermal case of open-framework metal phosphite, Zn3(HPO3)4·2C6H11N2, denoted NIS-3, was prepared using 1-ethyl-3-methyl imidazolium bromide as solvent and template.
Co-reporter:Jing-Dong Feng, Shu-Wei Tang, Kui-Zhan Shao, Rong-Shun Wang, Chan Yao, Hai-Ming Xie and Zhong-Min Su
CrystEngComm 2010 vol. 12(Issue 11) pp:3448-3451
Publication Date(Web):25 Jun 2010
DOI:10.1039/C002882G
A novel non-centrosymmetric zinc phosphate, Zn(HPO4)(H2PO4)·C6H11N2 (denoted NIS-4), was ionothermally synthesized. The framework exhibits fascinating helical channels and remarkably low framework density (FD). Meanwhile, an ionic liquid cation plays a significant structure-directing role during the course of crystallization.
Co-reporter:Jingyu Sun, Yizhen Tang, Xiujuan Jia, Fang Wang, Hao Sun, Yunju Zhang, ShuWei Tang, Fengdi Wang, Yingfei Chang, Yongji Lu, Xiumei Pan, Jingping Zhang and Rongshun Wang
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 36) pp:10846-10856
Publication Date(Web):26 Jul 2010
DOI:10.1039/C004284F
Singlet and triplet potential energy surfaces for the reactions of oxygen atoms (3P and 1D) with CF3CN have been studied computationally to evaluate the reaction mechanisms, possible products, and rate constants. On the triplet surface, six kinds of pathway are revealed, namely: direct fluorine abstraction, C-addition/elimination, N-addition/elimination, substitution, insertion and F-migration. The results show that the reaction should occur mainly through the C-addition/elimination mechanism involving the chemically activated CF3C(O)N* intermediate, and the major products are CF3 and NCO. The rate constants for C-addition/elimination channel of the reaction of O(3P) with CF3CN have been determined by using RRKM statistical rate theory and compared with the experimental data. On the singlet surface, the atomic oxygen can easily insert into the C–F or C–C bond of CF3CN, forming the insertion intermediates FOCF2CN and CF3OCN, and O(1D) can add to the carbon or nitrogen atom of the CN group in CF3CN, forming the addition intermediates CF3C(O)N and CF3CNO; both approaches are found to be barrierless. The decomposition and isomerization of some intermediates were also modeled at the QCISD(T)/6-311+G(2df)//B3LYP/6-311+G(d) level for the better understanding of the O(1D) with CF3CN chemistry. The decomposition products CF3 and NCO arising from CF3OCN and CF3NCO are the dominant species. Further comparison with similar reactions is also summarized.
Co-reporter:Xiu-Juan Jia;You-Jun Liu;Jing-Yu Sun;Hao Sun
Theoretical Chemistry Accounts 2010 Volume 127( Issue 1-2) pp:49-56
Publication Date(Web):2010 September
DOI:10.1007/s00214-009-0702-1
The mechanisms of CH2I with NO2 reaction were investigated on the singlet and triplet potential energy surfaces (PESs) by the UB3LYP method. The energetic information is further refined at the UCCSD(T) and UQCISD(T) levels of theory. Our results indicated that the title reaction is more favorable on the singlet PES thermodynamically, and less competitive on the triplet one. On the singlet PES, the title reaction is most likely to be initiated by the carbon-to-oxygen approach forming the adduct IM1 (H2ICONO-trans) without any transition state, which can isomerizes to IM2 (H2ICNO2) and IM3 (H2ICONO-cis), respectively. The most feasible pathway is the 1, 3-I shift with C–I and O–N bonds cleavage along with the N–I bond formation of IM1 lead to the product P1 (CH2O + INO), which can further dissociate to give P3 (CH2O + I + NO). The competitive pathway is 1, 3-H shift associated with O–N bond rupture of IM1 to form P2 (CHIO + HNO). The theoretically obtained major product CH2O and adducts IM1 and IM2 are in good agreement with the kinetic detection in experiment. The similarities and discrepancies between CH2I + NO2 and CH2Br + NO2 reactions are discussed in terms of the electronegativity of halogen atom and the barrier height of the rate-determining process. The present study may be helpful for further experimental investigation of the title reaction.
Co-reporter:Xiujuan Jia, Youjun Liu, Jingyu Sun, Hao Sun, Zhongmin Su, Xiumei Pan and Rongshun Wang
The Journal of Physical Chemistry A 2010 Volume 114(Issue 1) pp:417-424
Publication Date(Web):December 1, 2009
DOI:10.1021/jp908228h
A dual-level direct dynamic method is employed to study the reaction mechanisms of CF3CHFOCF3 (HFE-227 mc) with the OH radical and Cl atom. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the BH&H-LYP/6-311G(d,p) level, and the energetic information along the MEPs is further refined by MC-QCISD theory. The classical energy profile is corrected by the interpolated single-point energies (ISPE) approach, incorporating the small-curvature tunneling effect (SCT) calculated by the variational transition state theory (VTST). The rate constants are in good agreement with the experimental data and are found to be k1 = 2.87 × 10−21T2.80 exp(−1328.60/T) and k2 = 3.26 × 10−16T1.65 exp(−4642.76/T) cm3 molecule−1 s−1 over the temperature range 220−2000 K. The standard enthalpies of formation for the reactant CF3CHFOCF3 and product radical CF3CFOCF3 are evaluated via group-balanced isodesmic reactions, and the corresponding values are −454.06 ± 0.2 and −402.74 ± 0.2 kcal/mol, respectively, evaluated by MC-QCISD theory based on the BH&H-LYP/6-311G(d, p) geometries. The theoretical studies provide rate constants of the title reactions and the enthalpies of formation of the species, which are important parameters in determining the atmospheric lifetime and the feasible pathways for the loss of HFE-227 mc.
Co-reporter:Fang Wang, Hao Sun, Jingyu Sun, Xiujuan Jia, Yunju Zhang, Yizhen Tang, Xiumei Pan, Zhongmin Su, Lizhu Hao and Rongshun Wang
The Journal of Physical Chemistry A 2010 Volume 114(Issue 10) pp:3516-3522
Publication Date(Web):February 23, 2010
DOI:10.1021/jp910754b
Both singlet and triplet potential energy surfaces for the reaction of ground-state formaldehyde (CH2O) and ozone (O3) are theoretically investigated at the BMC-CCSD//BHandHLYP/6-311+G(d,p) level. Various possible isomerization and dissociation pathways are probed. Hydrogen abstraction, oxygen abstraction, and C-addition/elimination are found on both the singlet and the triplet surfaces. The major products for the total reaction are HCO and HOOO, which are generated via hydrogen abstraction. The transition state theory (TST) and multichannel RRKM calculations have been carried out for the total and individual rate constants for determinant channels over a wide range of temperatures and pressures.
Co-reporter:Hao Sun;Hongwei Gong;Huiling Liu;Fang Wang;Xiumei Pan
Theoretical Chemistry Accounts 2010 Volume 126( Issue 1-2) pp:15-25
Publication Date(Web):2010 May
DOI:10.1007/s00214-009-0646-5
The structures, energetics, dipole moments, vibrational spectra, rotational constants, and isomerization of singlet SiC4 isomers were explored using ab initio methods. Five types of isomers, a total of 11 minima, connected by 11 interconversion transition states, were located on the potential energy surface at the MP2/6-311G(d, p) level. More accurate energies were obtained at the G3(MP2) level. With the highest isomerization barrier, a C2v tetra-angular cone possesses the largest kinetic stability. The lowest-lying structure, linear SiCCCC is also highly kinetically stabilized. Besides, D2d bicyclic c-Si(CC)2, C2v five-membered ring c-SiCCCC, another C2v tetra-angular cone isomer and C3v trigonal bipyramid isomer are also considered to be kinetically stable, because their isomerization barriers are all over 10 kcal/mol. Other isomers cannot be kinetically stabilized with considerably low isomerization barriers. Investigation on the vibrational spectra, dipole moments, and rotational constants for SiC4 isomers are valuable for their detections in the interstellar space and laboratory.
Co-reporter:Li-Qun Sun, Ming-Juan Li, Rui-Hui Cui, Hai-Ming Xie and Rong-Shun Wang
The Journal of Physical Chemistry C 2010 Volume 114(Issue 7) pp:3297-3303
Publication Date(Web):February 1, 2010
DOI:10.1021/jp910422g
An optimum nanomicro structure of LiFePO4/o-polyacene (LiFePO4/O-PAS) with a high proportion of ortho linkages has been constructed using special processing technologies. O-PAS produces a thin, uniform conductive network because of its unique structure with low-branching and long-range order. The nanomicro structure of the composite cooperates with O-PAS to improve the electronic conductivity and lithium ion mobility, decrease the specific surface area, and improve the quality of the prepared electrode, which are the key factors for the large scale manufacture of lithium iron phosphate materials.
Co-reporter:Shu-Wei Tang, Jing-Dong Feng, Li-Li Sun, Feng-Di Wang, Hao Sun, Ying-Fei Chang, Rong-Shun Wang
Journal of Molecular Graphics and Modelling 2010 Volume 28(Issue 8) pp:891-898
Publication Date(Web):June 2010
DOI:10.1016/j.jmgm.2010.03.009
A systematic study on the geometrical structures and electronic properties of C68X4 (X = H, F, and Cl) fullerene compounds has been carried out on the basis of density functional theory. In all classical C68X4 isomers with two adjacent pentagons and one quasifullerene isomer [Cs:C68(f)] containing a heptagon in the framework, the Cs:0064 isomers are most favorable in energy. The addition reaction energies of C68X4 (Cs:0064) are high exothermic, and C68F4 is more thermodynamically accessible. The C68X4 (Cs:0064) possess strong aromatic character, with nucleus independent chemical shifts ranging from −22.0 to −26.1 ppm. Further investigations on electronic properties indicate that C68F4 and C68Cl4 could be excellent electron-acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities (3.29 and 3.15 eV, respectively). The Mulliken charge populations and partial density of states are also calculated, which show that decorating C68 fullerene with various X atoms will cause remarkably different charge distributions in C68X4 (Cs:0064) and affect their electronic properties distinctly. Finally, the infrared spectra of the most stable C68X4 (Cs:0064) molecules are simulated to assist further experimental characterization.
Co-reporter:L.Q. Sun, R.H. Cui, A.F. Jalbout, M.J. Li, X.M. Pan, R.S. Wang, H.M. Xie
Journal of Power Sources 2009 Volume 189(Issue 1) pp:522-526
Publication Date(Web):1 April 2009
DOI:10.1016/j.jpowsour.2008.10.120
Nano-crystallized LiFePO4 has been synthesized with a simple three-step-synthesis technology in the presence of nano-ferric oxide as iron source and polyacence (PAS) as a reductive agent and high conductive carbon source. The use of PAS increases the conductivity and prevents the particles growth. The most feasible calcined temperature and time was investigated and the best cell performance was delivered by the sample calcined at 700 °C for 4 h. This material shows excellent specific capacity and cycle efficiency at high current rates, almost no capacity loss can be observed up to 100 cycles which make it more superior as an optimum power cell cathode material.
Co-reporter:Kui-Zhan Shao, Ya-Hui Zhao, Xin-Long Wang, Ya-Qian Lan, De-Jun Wang, Zhong-Min Su and Rong-Shun Wang
Inorganic Chemistry 2009 Volume 48(Issue 1) pp:10-12
Publication Date(Web):December 5, 2008
DOI:10.1021/ic801439q
A polynuclear zinc compound, [Zn7(BTA)7(OABDC)(μ3-OH)2(μ2-OH)2·H2O] (1), has been prepared by using benzotriazole (HBTA) and 5-oxyacetatoisophthalic acid (H3OABDC) as ligands under hydrothermal conditions. For compound 1, an unprecedented metallophthalocyanine-like “Zn2(μ3-OH)2⊂[Zn4BTA4]” subunit is constructed from η3-BTA ligands and Zn atoms and further linked via μ2-OH, outer four-connected Zn atoms, and 5-oxyacetateisophthalic acid to form a novel three-dimensional framework.
Co-reporter:Jiawei Wang, Jing Liu, Guiling Yang, Xianfa Zhang, Xuedong Yan, Xiumei Pan, Rongshun Wang
Electrochimica Acta 2009 Volume 54(Issue 26) pp:6451-6454
Publication Date(Web):1 November 2009
DOI:10.1016/j.electacta.2009.05.002
Polyethylene glycol (PEG, mean molecular weight of 10,000) has been used to prepare a Li3V2(PO4)3/C cathode material by a simple solid-state reaction. The Raman spectra shows that the coating carbon has a good structure with a low ID/IG ratio. The images of SEM and TEM show that the carbon is dispersed between the Li3V2(PO4)3 particles, which improves the electrical contact between the corresponding particles. The electronic conductivity of Li3V2(PO4)3/C composite is 7.0 × 10−1 S/cm, increased by seven orders of magnitude compared with the pristine Li3V2(PO4)3 (2.3 × 10−8 S/cm). At a low discharge rate of 0.28C, the sample presents a high discharge capacity of 131.2 mAh/g, almost achieving the theoretical capacity (132 mAh/g) for the reversible cycling of two lithium. After 500 cycles, the discharge capacity is 123.9 mAh/g with only 5.6% fading of the initial specific capacity. The Li3V2(PO4)3/C material also exhibits an excellent rate capability with high discharge capacities of 115.2 mAh/g at 1C and 106.4 mAh/g at 5C.
Co-reporter:Xuedong Yan, Guiling Yang, Jing Liu, Yucui Ge, Haiming Xie, Xiumei Pan, Rongshun Wang
Electrochimica Acta 2009 Volume 54(Issue 24) pp:5770-5774
Publication Date(Web):1 October 2009
DOI:10.1016/j.electacta.2009.05.048
The cathode material is synthesized from FeC2O4·2H2O and LiH2PO4 by a solid-state reaction using citric acid as a carbon source. The electric conductivity of the synthesized LiFePO4 has been raised by eight orders of magnitude from 10−9 S cm−1. The LiFePO4/C composite shows a greatly enhanced rate performance and the cyclic stability at room temperature. It delivers an initial discharge capacity of 128 mAh g−1 at 4C, which is retained as high as 92% after 1000 cycles. In addition, the tested low temperature character is attractive. At −20 °C, the composite exhibits a discharge capacity of 110 mAh g−1 at 0.1C. The homogenous morphology, the porous surface, the small particles inside and the conductive carbon observed contribute much to obtain the favorable electrochemical performance.
Co-reporter:Jing Liu, Jiawei Wang, Xuedong Yan, Xianfa Zhang, Guiling Yang, Abraham F. Jalbout, Rongshun Wang
Electrochimica Acta 2009 Volume 54(Issue 24) pp:5656-5659
Publication Date(Web):1 October 2009
DOI:10.1016/j.electacta.2009.05.003
A simple high-energy ball milling combined with spray-drying method has been developed to synthesize LiFePO4/carbon composite. This material delivers an improved tap density of 1.3 g/cm3 and a high electronic conductivity of 10−2 to 10−3 S/cm. The electrochemical performance, which is especially notable for its high-rate performance, is excellent. The discharge capacities are as high as 109 mAh/g at the current density of 1100 mA/g (about 6.5C rate) and 94 mAh/g at the current density of 1900 mA/g (about 11C rate). At the high current density of 1700 mA/g (10C rate), it exhibits a long-term cyclability, retaining over 92% of its original discharge capacity beyond 2400 cycles. Therefore, the as-prepared LiFePO4/carbon composite cathode material is capable of such large-scale applications as hybrid and plug-in hybrid electric vehicles.
Co-reporter:Xianfa Zhang, Jiawei Wang, Zijia Yu, Rongshun Wang, Haiming Xie
Materials Letters 2009 Volume 63(Issue 28) pp:2523-2525
Publication Date(Web):30 November 2009
DOI:10.1016/j.matlet.2009.09.001
Porous carbon material with high surface area and highly mesoporous structure has been successfully prepared from phenol–formaldehyde resin by combining Polyethylene Glycol (PEG) and ZnCl2 as activation agents. The as-prepared carbon material exhibits large specific double layer capacitance of 122 F g− 1 at 120 mA g− 1 in the electrolyte of 1 M Et4NBF4/PC, which is attributed to its high specific surface area and well-developed mesopores. Moreover, it can retain as high as 86.88% of its initial specific capacitance, when the specific current increases from 120 mA g− 1 to 2 A g− 1. It is also found that the energy density of this material still maintains up to 21.2 Wh kg− 1 at the power density of 2400 W kg− 1.
Co-reporter:Hao Sun, Hongwei Gong, Xiumei Pan, Lizhu Hao, ChiaChung Sun, Rongshun Wang and Xuri Huang
The Journal of Physical Chemistry A 2009 Volume 113(Issue 20) pp:5951-5957
Publication Date(Web):April 27, 2009
DOI:10.1021/jp9006262
A direct ab initio dynamics method was used to study the mechanism and kinetics of the reaction CF3CHFOCH3 + OH. Two reaction channels, R1 and R2, were found, corresponding to H-abstraction from a —CH3 group and a —CHF group, respectively. The potential energy surface (PES) information was obtained at the G3(MP2)//MP2/6-311G(d,p) level. The standard enthalpies of formation for the reactant (CF3CHFOCH3) and products (CF3CHFOCH2 and CF3CFOCH3) were evaluated via isodesmic reactions at the same level. Furthermore, the rate constants of two channels were calculated using the canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions over a wide temperature range of 200−3000 K. The dynamic calculations demonstrate that reaction R1 dominates the overall reaction when the temperature is lower than 800 K whereas reaction R2 becomes more competitive in the higher temperature range. The calculated rate constants and branching ratios are both in good agreement with the available experimental values.
Co-reporter:Xiu-Juan Jia;You-Jun Liu;Jing-Yu Sun;Yi-Zhen Tang
Theoretical Chemistry Accounts 2009 Volume 124( Issue 1-2) pp:105-113
Publication Date(Web):2009 September
DOI:10.1007/s00214-009-0587-z
Theoretical investigations are carried out on the reaction Cl + CH2FCl by means of direct dynamics method. The minimum energy path (MEP) is obtained at the MP2/6-311G(d, p) level. The energetic information is further improved by single-point energy calculations using QCISD(T)/6-311++G(d, p) method. The kinetics of this reaction are calculated by canonical variational transition state theory incorporating with the small-curvature tunneling correction over a wide temperature range of 220–3,000 K, and rate constant expression are found to be k(T) = 1.48 × 10−17T2.04exp(−913.91/T). For the title reaction, H-abstraction reaction channel is the major channel at the lower temperatures. At higher temperatures, the contribution of Cl-abstraction reaction channel should be taken into account.
Co-reporter:Xiu-Juan Jia;Xiu-Mei Pan;Jing-Yu Sun;Yi-Zhen Tang
Theoretical Chemistry Accounts 2009 Volume 122( Issue 3-4) pp:207-216
Publication Date(Web):2009 March
DOI:10.1007/s00214-008-0500-1
The radical-molecule reaction mechanisms of CH2Br and CHBrCl with NO2 have been explored theoretically at the UB3LYP/6-311G(d, p) level. The single-point energies were calculated using UCCSD(T) and UQCISD(T) methods. The results show that the title reactions are more favorable on the singlet potential energy surface than on the triplet one. For the singlet potential energy surface of CH2Br + NO2 reaction, the association of CH2Br with NO2 is found to be a barrierless carbon-to-oxygen attack forming the adduct IM1 (H2BrCONO-trans), which can isomerize to IM2 (H2BrCNO2), and IM3 (H2BrCONO-cis), respectively. The most feasible pathway is the 1, 3-Br shift with C–Br and O–N bonds cleavage along with the N–Br bond formation of IM1 lead to the product P1 (CH2O + BrNO) which can further dissociate to give P4 (CH2O + Br + NO). The competitive pathway is the 1, 3-H-shift associated with O–N bond rupture of IM1 to form P2 (CHBrO + HNO). For the singlet potential energy surface of CHBrCl + NO2 reaction, there are three important reaction pathways, all of which may have comparable contribution to the reaction of CHBrCl with NO2. The theoretically obtained major products CH2O and CHClO for CH2Br + NO2 and CHBrCl + NO2 reactions, respectively, are in good agreement with the kinetic detection in experiment.
Co-reporter:Yi-Zhen Tang;Ya-Ru Pan;Bing He;Jing-Yu Sun
Theoretical Chemistry Accounts 2009 Volume 122( Issue 1-2) pp:67-76
Publication Date(Web):2009 January
DOI:10.1007/s00214-008-0485-9
The mechanisms of CH2SH with NO2 reaction were investigated on the singlet and triplet potential energy surfaces (PES) at the BMC-CCSD//B3LYP/6-311 + G(d,p) level. The result shows that the title reaction is more favourable on the singlet PES thermodynamically, and it is less competitive on the triplet PES. On the singlet PES, the initial addition of CH2SH with NO2 leads to HSCH2NO2 (IM2) without any transition state, followed by a concerted step involving C–N fission and shift of H atom from S to O giving out CH2S + trans-HONO, which is the major products of the title reaction. With higher barrier height, the minor products are CH2S + HNO2, formed by a similar concerted step from the initial adduct HSCH2ONO (IM1). The direct abstraction route of H atom in SH group abstracted by O atom might be of some importance. It starts from the addition of the reactants to form a weak interaction molecular complex (MC3), subsequently, surmounts a low barrier height leading to another complex (MC2), which gives out CH2S + trans-HONO finally. Other direct hydrogen abstraction channels could be negligible with higher barrier heights and less stable products.
Co-reporter:Haiying Yu, Xianfa Zhang, A.F. Jalbout, Xuedong Yan, Xiumei Pan, Haiming Xie, Rongshun Wang
Electrochimica Acta 2008 Volume 53(Issue 12) pp:4200-4204
Publication Date(Web):1 May 2008
DOI:10.1016/j.electacta.2007.12.052
In recent years, spinel lithium titanate (Li4Ti5O12) as a superior anode material for energy storage battery has attracted a great deal of attention because of the excellent Li-ion insertion and extraction reversibility. However, the high-rate characteristics of this material should be improved if it is used as an active material in large batteries. One effective way to achieve this is to prepare electrode materials coated with carbon. A Li4Ti5O12/polyacene (PAS) composite were first prepared via an in situ carbonization of phenol–formaldehyde (PF) resin route to form carbon-based composite. The SEM showed that the Li4Ti5O12 particles in the composite were more rounded and smaller than the pristine one. The PAS was uniformly dispersed between the Li4Ti5O12 particles, which improved the electrical contact between the corresponding Li4Ti5O12 particles, and hence the electronic conductivity of composite material. The electronic conductivity of Li4Ti5O12/PAS composite is 10−1 S cm−1, which is much higher than 10−9 S cm−1 of the pristine Li4Ti5O12. High specific capacity, especially better high-rate performance was achieved with this Li4Ti5O12/PAS electrode material. The initial specific capacity of the sample is 144 mAh/g at 3 C, and it is still 126.2 mAh/g after 200 cycles. By increasing the current density, the sample still maintains excellent cycle performance.
Co-reporter:Kui-Zhan Shao, Ya-Hui Zhao, Yan Xing, Ya-Qian Lan, Xin-Long Wang, Zhong-Min Su and Rong-Shun Wang
Crystal Growth & Design 2008 Volume 8(Issue 8) pp:2986
Publication Date(Web):July 18, 2008
DOI:10.1021/cg800103b
A novel chiral coordination polymer with a bikitaite zeolite framework has been constructed based on asymmetrical tetrahedral building blocks, in which the original chiralities derive from the configurational effect of benzotriazole ligands and transfer to the whole network through four distinct single helical chains.
Co-reporter:Yi-Zhen Tang;Jing-Yu Sun;Hao Sun;Ya-Ru Pan
Theoretical Chemistry Accounts 2008 Volume 119( Issue 4) pp:297-303
Publication Date(Web):2008 March
DOI:10.1007/s00214-007-0383-6
The mechanisms of the reaction of NCCO with molecular oxygen are investigated at the G3MP2//B3LYP/6-311G(d,p) levels for the first time. The calculation results show that two mechanisms are involved, namely, O attack on α atom mechanism and O attack on β atom mechanism, with six products yielded. The most feasible channel is the addition of O2 to β atom in NCCO radical leading to the energy-rich intermediate IM1, NCC(O)OO, which can isomerize to a four-center-structure IM3, and then undergoes C–C and O–C bond fission to form P1(NCO + CO2) finally. The barriers are 27.3 and 25.4 kcal/mol, respectively. For other channels involved in the two mechanisms, with less stable initial adducts and higher barrier, they are less conceivable dynamically and thermochemically.
Co-reporter:Hao Sun;Nannan Tan;Hongqing He;Xiumei Pan;Zhongmin Su
Theoretical Chemistry Accounts 2008 Volume 119( Issue 5-6) pp:501-509
Publication Date(Web):2008 April
DOI:10.1007/s00214-008-0415-x
The calculations of the geometry optimizations, energies, dipole moments, vibrational spectra, rotational constants, and isomerization of doublet SiC3H species were performed using density functional theory and ab initio methods. Four types of isomers, a total of 18 minima, connected by 16 interconversion transition states, were located on the potential energy surface (PES) at the B3LYP/6-311G (d, p) level. More accurate energies were obtained at the CCSD(T)/6-311G(2df, 2p), and G3(MP2) levels. With the highest isomerization barrier, the lowest lying structure, linear A1 possesses the largest kinetic stability. Besides, the isomerization barriers of A2, A4, C2, F1, F4 and F5 are over 10 kcal/mol, and these isomers are also considered to be higher kinetically stable. Other isomers cannot be kinetically stabilized with considerably low isomerization barriers. Investigation on the bonding properties and the computations of vibrational spectra, dipole moments, and rotational constants for SiC3H isomers are helpful for understanding their structures and also valuable for their detections in the interstellar space and laboratory.
Co-reporter:Jing-Yu Sun;Yi-Zhen Tang;Hao Sun;Xiu-Juan Jia
Theoretical Chemistry Accounts 2008 Volume 121( Issue 1-2) pp:33-41
Publication Date(Web):2008 September
DOI:10.1007/s00214-008-0443-6
A detailed computational study has been performed on the mechanism and kinetics of the C2H + CH3CN reaction. The geometries were optimized at the BHandHLYP/6–311G(d, p) level. The single-point energies were calculated using the BMC-CCSD, MC-QCISD and QCISD(T)/6–311+G(2df, 2pd) methods. Five mechanisms were investigated, namely, direct hydrogen abstraction, C-addition/elimination, N-addition/elimination, C2H–to–CN substitution and H-migration. The kinetics of the title reaction were studied using TST and multichannel RRKM methodologies over a wide range of temperatures (150–3,000 K) and pressures (10−4–104 torr). The total rate constants show positive temperature dependence and pressure independence. At lower temperatures, the C-addition step is the most feasible channel to produce CH3 and HCCCN. At higher temperatures, the direct hydrogen abstraction path is the dominant channel leading to C2H2 and CH2CN. The calculated overall rate constants are in good agreement with the experimental data.
Co-reporter:Yi-Zhen Tang;Ya-Ru Pan;Jing-Yu Sun;Hao Sun
Theoretical Chemistry Accounts 2008 Volume 121( Issue 3-4) pp:201-207
Publication Date(Web):2008 October
DOI:10.1007/s00214-008-0466-z
The mechanism for the CH2SH + O2 reaction was investigated by DFT and ab initio chemistry methods. The geometries of all possible stationary points were optimized at the B3LYP/6-311+G(d,p) level, and the single point energy was calculated at the CCSD(T)/cc-pVXZ(X = D and T), G3MP2 and BMC-CCSD levels. The results indicate that the oxidation of CH2SH by O2 to form HSCH2OO is a barrierless process. The most favorable channel is the rearrangement of the initial adduct HSCH2OO (IM1) to form another intermediate H2C(S)OOH (IM3) via a five-center transition state, and then the C–O bond fission in IM3 leads to a complex CH2S. . .HO2 (MC1), which finally gives out to the major product CH2S + HO2. Due to high barriers, other products including cis- and trans-HC(O)SH + HO could be negligible. The direct abstraction channel was also determined to yield CH2S + HO2, with the barrier height of 22.3, 18.1 and 15.0 kcal/mol at G3MP2, CCSD(T)/cc-pVTZ and BMC-CCSD levels, respectively, it is not competitive with the addition channel, in which all stationary points are lower than reactant energetically. The other channels to produce cis- and trans-CHSH + HO2 are also of no importance.
Co-reporter:Yizhen Tang, Rongshun Wang and Baoshan Wang
The Journal of Physical Chemistry A 2008 Volume 112(Issue 23) pp:5295-5299
Publication Date(Web):May 14, 2008
DOI:10.1021/jp800394h
Mechanisms and kinetics of the NCCO + O2 reaction have been investigated using the extrapolated full coupled cluster theory with the complete basis set limit (FCC/CBS) and multichannel RRKM theory. Energetically, the most favorable reaction route involves the barrierless addition of the oxygen atom to one of the carbon atoms of NCCO and the subsequent isomerization−decomposition via the four-center intermediate and transition state, leading to the final products NCO and CO2. At 298 K, the calculated overall rate constant is strongly pressure-dependent, which is in good agreement with the available experimental values. It is predicted that the high-pressure limit rate constants exhibit negative temperature dependence below 350 K. The dominant products are NCO and CO2 at low pressures (ca. <10 Torr) and the NCCO(O2) radical at higher pressures, respectively.
Co-reporter:Yizhen Tang, Hao Sun, Jingyu Sun, Yaru Pan, Zesheng Li, Rongshun Wang
Chemical Physics 2007 Volume 337(1–3) pp:119-124
Publication Date(Web):16 August 2007
DOI:10.1016/j.chemphys.2007.07.003
Abstract
A direct dynamics method is employed to study the mechanism and kinetics of the hydrogen abstraction reaction of C2H5OH with NCO. The optimized geometries and frequencies of the stationary points and the minimum-energy paths (MEPs) are obtained at the MP2/6-311G(d,p) level. In order to obtain more accurate potential energy surface (PES) information and provide more credible energy data for kinetic calculation, the single-point energies along the MEPs are further computed at QCISD(T)/6-311+G(d,p)//MP2/6-311G(d,p) level. The rate constants for three channels of title reaction are calculated by canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions over the wide temperature region 220–1500 K. The theoretical overall rate constants are in good agreement with the available experimental data. For the title reaction, the methylene–H abstraction channel is dominant, while the hydroxyl-H and methyl-H abstraction channels are negligible over the whole temperature region.
Co-reporter:H.-M. Xie;L.-Y. Zhang;J.-R. Ying;R.-S. Wang;A. F. Jalbout;X.-M. Pan;G.-L. Yang;Z.-M. Su;H.-Y. Yu
Advanced Materials 2006 Volume 18(Issue 19) pp:2609-2613
Publication Date(Web):26 SEP 2006
DOI:10.1002/adma.200600578
A novel core/shell compound has been developed by coating a spherical LiFePO4 structure with a specific π-bond character planar polymer (polyacene, PAS). The electronic conductivity, low-temperature character, and tap density of the LiFePO4–PAS composite were significantly improved compared to LiFePO4, which may lead to use in lithium-ion battery applications.
Co-reporter:Hao Sun, Hongqing He, Hongwei Gong, Xiumei Pan, Zesheng Li, Rongshun Wang
Chemical Physics 2006 Volume 327(Issue 1) pp:91-97
Publication Date(Web):21 August 2006
DOI:10.1016/j.chemphys.2006.03.033
Abstract
A direct ab initio dynamics method is performed to study the mechanism and kinetics of the hydrogen abstraction reaction of CH3CH2F with OH. One transition state is located for α-H abstraction reaction, and two are identified for β-H abstraction. The optimized geometries and frequencies of the stationary points and the minimum-energy paths (MEPs) are calculated at the MP2/6-311G(d,p) level. To verify the reliability of MP2/6-311G(d,p) geometries, the optimizations of the reactants, products and transition states are also performed at the MPW1K/6-311+G(2df,2p) level. In order to obtain the more accurate potential energy surface (PES) information and provide more credible energy data for kinetic calculation, the single-point energies along the MEPs are further refined at G3 level based on the optimized geometries. The rate constants of the three channels are evaluated by using the canonical variational transition-state theory (CVT) with small-curvature tunneling (SCT) correction method over a wide temperature range of 210–3500 K.
Co-reporter:Yingfei Chang, Abraham F. Jalbout, Jingping Zhang, Zhongmin Su, Rongshun Wang
Chemical Physics Letters 2006 Volume 428(1–3) pp:148-151
Publication Date(Web):8 September 2006
DOI:10.1016/j.cplett.2006.06.091
A series of B3LYP/6-31G∗ calculations reveal that the D3 isomer is the most stable isomer of C32 carbon cages. The derivatives of it, including additional productions (C32H2, C32Cl2), hetero-fullerenes (C30B2, C30N2), isoelectronic molecules (C30B22-, C30N22+) and dimers have been investigated at the same level. The results show that, the additional hydrogen atoms and replaced nitrogen atoms can enhance the electronic stabilization of D3 C32. Our calculations suggest that the building block of C32 oligomers which linked by sp3 bonds should be the saturated C32H2 unit.The derivatives of D3 C32 (the most stable isomer of C32 fullerenes) including additional productions (C32H2, C32Cl2), hetero-fullerenes (C30B2, C30N2), isoelectronic molecules (C30B22-, C30N22+) and dimers have been investigated by using the DFT method.
Co-reporter:Hai-ming XIE, Xue-dong VAN, Hai-ying YU, Ling-yun ZHANG, Gui-ling YANG, Yang XU, Rong-shun WANG
Chemical Research in Chinese Universities 2006 Volume 22(Issue 5) pp:639-642
Publication Date(Web):September 2006
DOI:10.1016/S1005-9040(06)60179-7
Co-reporter:Hao Sun, Yizhen Tang, Zhanliang Wang, Xiumei Pan, Zesheng Li, Rongshun Wang
Journal of Molecular Structure: THEOCHEM 2005 Volume 757(1–3) pp:143-148
Publication Date(Web):30 December 2005
DOI:10.1016/j.theochem.2005.09.018
A detailed theoretical survey on the potential energy surface for the CH2CO+NCX(X=O, S) reaction is carried out at the QCISD/6-311+G(d, p)//B3LYP/6-311+G (d, p) level. The geometries, vibrational frequencies and energies of all stationary points involved in the reactions are calculated at the B3LYP/6-311+G(d, p) level. And the more accurate energy information is provided by single point calculations at the QCISD(T)/6-311+G(d, p) level. Relationships of the reactants, transition states, intermediates and products are confirmed by the intrinsic reaction coordinate (IRC) calculations. The calculations suggest that the channel producing CH2NCO+CO is the dominant one, and CH2NCO+CO is the major product for the CH2CO+NCO reaction. The results are in good agreement with experiments. And similarly, product CH2NCS+CO is the most important product for the CH2CO+NCS reaction.
Co-reporter:Min Zhao;Yan-Ling Zhao;Peng-Jun Liu;Ying-Fei Chang;Xiu-Mei Pan;Zhong-Min Su
Chinese Journal of Chemistry 2004 Volume 22(Issue 6) pp:
Publication Date(Web):26 AUG 2010
DOI:10.1002/cjoc.20040220623
The reaction mechanism of OBrO with OH has been studied using the B3LYP/6-311+G(d,p) and the high-level electron-correlation CCSD(T)/6-311+G(d,p) at single-point. The results show that the title reaction could probably proceed by four possible schemes, generating HOBr+O2, HBr+O3, BrO+HO2 and HOBrO2 products, respectively. The main channel is the one to yield HOBr + O2. The whole reaction involves the formation of three-membered, four-membered and five-membered rings, followed by the complicated processes of association, H-shift, Br-shift and dissociation. All routes are exothermic.
Co-reporter:Y.L. Zhao, R.Q. Zhang, R.S. Wang
Chemical Physics Letters 2004 Volume 398(1–3) pp:62-67
Publication Date(Web):1 November 2004
DOI:10.1016/j.cplett.2004.09.078
Abstract
Three representative aromatic carbon compounds, C6H6, C10H8 and C13H9, are chosen to simulate H2 adsorptions in aromatic carbon materials. The calculations of H2 locating on top of the hexagon center, middle of C–C bond and a C atom of these compounds using density functional and the second order Møller–Plesset perturbation theories indicate that the bindings of H2 with these compounds are very weak. However, the binding is significantly enhanced when lithium is introduced between the H2 and the aromatic carbon compound. In particular, the binding energy of H2 at Li adsorbed on top of the C13H9 is as large as 2.5 kcal mol−1, one order of magnitude enhanced. Such a stable H2 adsorption and the moderate adsorption energy facilitate good H2 storage. According to the similarity of surface features and chemical reactivities among the various aromatic carbon compounds and carbon nanotubes, we conjecture that the H2 storage in these materials would all be enhanced by introducing Li.
Co-reporter:Jingyu Sun, Yizhen Tang, Xiujuan Jia, Fang Wang, Hao Sun, Yunju Zhang, ShuWei Tang, Fengdi Wang, Yingfei Chang, Yongji Lu, Xiumei Pan, Jingping Zhang and Rongshun Wang
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 36) pp:NaN10856-10856
Publication Date(Web):2010/07/26
DOI:10.1039/C004284F
Singlet and triplet potential energy surfaces for the reactions of oxygen atoms (3P and 1D) with CF3CN have been studied computationally to evaluate the reaction mechanisms, possible products, and rate constants. On the triplet surface, six kinds of pathway are revealed, namely: direct fluorine abstraction, C-addition/elimination, N-addition/elimination, substitution, insertion and F-migration. The results show that the reaction should occur mainly through the C-addition/elimination mechanism involving the chemically activated CF3C(O)N* intermediate, and the major products are CF3 and NCO. The rate constants for C-addition/elimination channel of the reaction of O(3P) with CF3CN have been determined by using RRKM statistical rate theory and compared with the experimental data. On the singlet surface, the atomic oxygen can easily insert into the C–F or C–C bond of CF3CN, forming the insertion intermediates FOCF2CN and CF3OCN, and O(1D) can add to the carbon or nitrogen atom of the CN group in CF3CN, forming the addition intermediates CF3C(O)N and CF3CNO; both approaches are found to be barrierless. The decomposition and isomerization of some intermediates were also modeled at the QCISD(T)/6-311+G(2df)//B3LYP/6-311+G(d) level for the better understanding of the O(1D) with CF3CN chemistry. The decomposition products CF3 and NCO arising from CF3OCN and CF3NCO are the dominant species. Further comparison with similar reactions is also summarized.
Co-reporter:Jingyu Sun, Rongshun Wang and Baoshan Wang
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 37) pp:NaN16595-16595
Publication Date(Web):2011/08/17
DOI:10.1039/C1CP20836E
The mechanism and kinetics of the reaction of acrylonitrile (CH2CHCN) 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 CC double bond or C atom of –CN group to form the chemically activated adducts, 1-IM1(HOCH2CHCN), 2-IM1(CH2HOCHCN), and 3-IM1(CH2CHCOHN) 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 N2 as bath gas, 1-IM1(OHCH2CHCN) formed by collisional stabilization is the major product in the temperature range of 200–1200 K. The production of CH2CCN and CHCHCNviahydrogen abstractions becomes dominant at high temperatures (1200–3000 K).
Co-reporter:Yuhan Li, Jingping Zhang, Fengmei Yang, Jing Liang, Hao Sun, Shuwei Tang and Rongshun Wang
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 44) pp:NaN24609-24609
Publication Date(Web):2014/10/14
DOI:10.1039/C4CP03628J
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.
Co-reporter:Dai-Huo Liu, Hong-Yan Lü, Xing-Long Wu, Bao-Hua Hou, Fang Wan, Sheng-Da Bao, Qingyu Yan, Hai-Ming Xie and Rong-Shun Wang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 39) pp:NaN19746-19746
Publication Date(Web):2015/07/15
DOI:10.1039/C5TA03556B
Among the transition metal oxides as anode materials for lithium ion batteries (LIBs), the MnO material should be the most promising one due to its many merits mainly relatively low voltage hysteresis. However, it still suffers from inferior rate capabilities and poor cycle life arising from kinetic limitations, drastic volume changes and severe agglomeration of active MnO particulates during cycling. In this paper, by integrating the typical strategies of improving the electrochemical properties of transition metal oxides, we had rationally designed and successfully prepared one superior MnO-based nanohybrid (MnO@C/RGO), in which carbon-coated MnO nanoparticles (MnO@C NPs) were electrically connected by three-dimensional conductive networks composed of flexible graphene nanosheets. Electrochemical tests demonstrated that, the MnO@C/RGO nanohybrid not only showed the best Li storage performance in comparison with the commercial MnO material, MnO@C NPs and carbon nanotube enhanced MnO@C NPs, but also exhibited much improved electrochemical properties compared with most of the previously reported MnO-based materials. The superior electrochemical properties of the MnO@C/RGO nanohybrid included a high specific capacity (up to 847 mA h g−1 at 80 mA g−1), excellent high-rate capabilities (for example, delivering 451 mA h g−1 at a very high current density of 7.6 A g−1) and long cycle life (800 cycles without capacity decay). More importantly, for the first time, we had achieved the discharging/charging of MnO-based materials without capacity increase even after 500 cycles by adjusting the voltage range, making the MnO@C/RGO nanohybrid more possible to be a really practical anode material for LIBs.
