Xuebin Yu

Synthesis of uniform TiO2@carbon composite nanofibers as anode for lithium ion batteries with enhanced electrochemical performance

Very large area, uniform TiO2@carbon composite nanofibers were easily prepared by thermal pyrolysis and oxidization of electrospun titanium(IV) isopropoxide/polyacrylonitrile (PAN) nanofibers in argon. The composite nanostructures exhibit the unique feature of having TiO2 nanocrystals encapsulated inside a porous carbon matrix. The unique orderly-bonded nanostructure, porous characteristics, and highly conductive carbon matrix favour excellent electrochemical performance of the TiO2@carbon nanofiber electrode. The TiO2@carbon hybrid nanofibers exhibited highly reversible capacity of 206 mAh g−1 up to 100 cycles at current density of 30 mA g−1 and excellent cycling stability, indicating that the composite is a promising anode candidate for Li-ion batteries.

Significantly improved dehydrogenation of LiBH4 destabilized by TiF3

The hydrogen storage properties of LiBH4 ball milled with TiF3 were investigated. It was found that the LiBH4–TiF3 mixture exhibited significantly improved dehydrogenation properties. For example, the LiBH4–TiF3 (mole ratio: 3 : 1) sample started to release hydrogen at around 100 °C, and the hydrogen desorption capacity reached 5.0 wt% at 250 °C. Furthermore, the dehydrogenated product can be partially rehydrogenated at 100 atm H2 and 350 °C. X-Ray diffraction (XRD), infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) characterizations revealed that the decreased dehydrogenation conditions in the LiBH4–TiF3 system resulted from an exothermic reaction of 3LiBH4 + TiF3 → 3LiF + TiB2 + B + 6H2, which improved both its thermodynamics and kinetics. As the above reaction is exothermic, the reverse reaction is not feasible, further investigations indicated that the rehydrogenation may be due to the formation of another borohydride.

Graphene oxide based recyclable dehydrogenation of ammonia borane within a hybrid nanostructure.

The recyclable dehydrogenation of ammonia borane (AB) is achievable within a graphene oxide (GO)-based hybrid nanostructure, in which a combined modification strategy of acid activation and nanoconfinement by GO allows AB to release more than 2 equiv of pure H(2) at temperatures below 100 °C. This process yields polyborazylene (PB) as a single product and, thus, promotes the chemical regeneration of AB via reaction of PB with hydrazine in liquid ammonia.

Monodisperse magnesium hydride nanoparticles uniformly self-assembled on graphene.

Monodisperse MgH2 nanoparticles with homogeneous distribution and a high loading percent are developed through hydrogenation-induced self-assembly under the structure-directing role of graphene. Graphene acts not only as a structural support, but also as a space barrier to prevent the growth of MgH2 nanoparticles and as a thermally conductive pathway, leading to outstanding performance.

Structure and decomposition of zinc borohydride ammonia adduct: towards a pure hydrogen release

Zn(BH4)2·2NH3, a new ammine metal borohydride, has been synthesized via simply ball-milling a mixture of ZnCl2·2NH3/2LiBH4. Structure analysis shows that the subsequent complex has a monoclinic structure with unit-cell parameters of a = 6.392(4) A, b = 8.417(6) A, c = 6.388(4) A and β = 92.407(4)° and space group P21, in which Zn atoms coordinate with two BH4 groups and two NH3 groups. The interatomic distances reported herein show that Zn–H bonding in Zn(BH4)2·2NH3 is shorter than Ca–H bonds in Ca(BH4)2·2NH3 and Mg–H in Mg(BH4)2·2NH3. This reduced bond contact leads to an increase in the ionic character of H. This study is able to show a good correlation between the reduced M–H distance and enhanced dehydrogenation behavior of the hydride material. Dehydrogenation results showed that Zn(BH4)2·2NH3/LiCl is able to release 5.36 wt% hydrogen (corresponding to 8.9 wt% for pure Zn(BH4)2·2NH3) below 115 °C within 15 min without concomitant release of undesirable gases such as ammonia and/or boranes, thereby demonstrating the potential of Zn(BH4)2·2NH3 to be used as a solid hydrogen storage material.

Amminelithium Amidoborane Li(NH3)NH2BH3: A New Coordination Compound with Favorable Dehydrogenation Characteristics

The monoammoniate of lithium amidoborane, Li(NH(3))NH(2)BH(3), was synthesized by treatment of LiNH(2)BH(3) with ammonia at room temperature. This compound exists in the amorphous state at room temperature, but at -20 degrees C crystallizes in the orthorhombic space group Pbca with lattice parameters of a = 9.711(4), b = 8.7027(5), c = 7.1999(1) A, and V = 608.51 A(3). The thermal decomposition behavior of this compound under argon and under ammonia was investigated. Through a series of experiments we have demonstrated that Li(NH(3))NH(2)BH(3) is able to absorb/desorb ammonia reversibly at room temperature. In the temperature range of 40-70 degrees C, this compound showed favorable dehydrogenation characteristics. Specifically, under ammonia this material was able to release 3.0 equiv hydrogen (11.18 wt %) rapidly at 60 degrees C, which represents a significant advantage over LiNH(2)BH(3). It has been found that the formation of the coordination bond between ammonia and Li(+) in LiNH(2)BH(3) plays a crucial role in promoting the combination of hydridic B-H bonds and protic N-H bonds, leading to dehydrogenation at low temperature.

Dispersion of SnO2 nanocrystals on TiO2(B) nanowires as anode material for lithium ion battery applications

TiO2(B)@SnO2 core–shell hybrid nanowires have been synthesized by a facile hydrothermal process and subsequent liquid phase reaction. Hybrid nanowire electrodes exhibit excellent reversible lithium storage capacity rate capability and good cyclability, mainly due to the particular architecture of the composite, which features an open continuous channel along its axis, facilitating lithium ion diffusion, and provides effective mechanical support for the TiO2(B) core, alleviating the stress produced during discharge–charge cycling and also preventing the pulverization of the Sn nanoparticles. Owing to its superior electrochemical performance, this composite could be a promising potential anode material for lithium ion batteries.

TiO2(B)@carbon composite nanowires as anode for lithium ion batteries with enhanced reversible capacity and cyclic performance

Novel TiO2(B)@carbon composite nanowires were simply prepared by a two-step hydrothermal process with subsequent heat treatment in argon. The nanostructures exhibit the unique feature of having TiO2(B) encapsulated inside and an amorphous carbon layer coating the outside. The unique core/shell structure and chemical composition is likely to lead to perfect performance in many applications. In this paper, the results of Li-ion battery testing are presented to demonstrate the superior cyclic performance and rate capability of the TiO2(B)@carbon nanowires. The composite nanowires exhibit a high reversible capacity of 560 mAh g−1 after 100 cycles at the current density of 30 mA g−1, and excellent cycling stability and rate capability (200 mAh g−1 when cycled at the current density of 750 mA g−1), indicating that the composite is a promising anode candidate for Li-ion batteries.

Structure and hydrogen storage properties of the first rare-earth metal borohydride ammoniate: Y(BH4)3·4NH3

The ammine complex of yttrium borohydride Y(BH4)3·4NH3, which contains a theoretical hydrogen capacity of 11.9 wt.%, has been successfully synthesized via a simple ball milling of YCl3·4NH3 and LiBH4. The structure of Y(BH4)3·4NH3, determined by high resolution powder X-ray diffraction, crystallizes in the orthorhombic space group Pc21n with lattice parameters a = 7.1151(1) A, b = 11.4192(2) A, c = 12.2710(2) A and V = 997.02(2) A3, in which the dihydrogen bonds with distances in the range of 2.043 to 2.349 A occurred between the NH3 and BH4− units contribute to the hydrogen liberation via the combination reaction of N–H⋯H–B. Thermal gravimetric analysis combined with mass spectrometer results revealed that the decomposition of Y(BH4)3·4NH3 consists of three steps with peaks at 86 °C, 179 °C and 279 °C, respectively, in which the first and second steps mainly release hydrogen accompanied by a fair amount of ammonia emission, while the third one accounts for a pure hydrogen release. Isothermal dehydrogenation results revealed that over 8.7 wt.% hydrogen was released for Y(BH4)3·4NH3 at 200 °C, which are improved significantly in terms of both capacity and kinetics comparing to Y(BH4)3, in which the hydrogen capacity is only 3.2 wt.% at the same temperature. The favorable dehydrogenation properties presented by the Y(BH4)3·4NH3, i.e., lower dehydrogenation temperature and higher nominal hydrogen contents than that of Y(BH4)3, enable it to be a promising candidate for hydrogen storage. In addition, in situ high resolution X-ray diffraction, differential scanning calorimetry, solid-state 11B nuclear magnetic resonance and Fourier transform infrared spectroscopy measurements were employed to understand the dehydrogenation pathway of Y(BH4)3·4NH3.

A New Ammine Dual‐Cation (Li, Mg) Borohydride: Synthesis, Structure, and Dehydrogenation Enhancement

A new ammine dual-cation borohydride, LiMg(BH(4))(3)(NH(3))(2), has been successfully synthesized simply by ball-milling of Mg(BH(4))(2) and LiBH(4)·NH(3). Structure analysis of the synthesized LiMg(BH(4))(3)(NH(3))(2) revealed that it crystallized in the space group P6(3) (no. 173) with lattice parameters of a=b=8.0002(1) Å, c=8.4276(1) Å, α=β=90°, and γ=120° at 50 °C. A three-dimensional architecture is built up through corner-connecting BH(4) units. Strong N-H···H-B dihydrogen bonds exist between the NH(3) and BH(4) units, enabling LiMg(BH(4))(3)(NH(3))(2) to undergo dehydrogenation at a much lower temperature. Dehydrogenation studies have revealed that the LiMg(BH(4))(3)(NH(3))(2)/LiBH(4) composite is able to release over 8 wt% hydrogen below 200 °C, which is comparable to that released by Mg(BH(4))(3)(NH(3))(2). More importantly, it was found that release of the byproduct NH(3) in this system can be completely suppressed by adjusting the ratio of Mg(BH(4))(2) and LiBH(4)·NH(3). This chemical control route highlights a potential method for modifying the dehydrogenation properties of other ammine borohydride systems.