Hailiang Chu

Stepwise phase transition in the formation of lithium amidoborane.

A stepwise phase transition in the formation of lithium amidoborane via the solid-state reaction of lithium hydride and ammonia borane has been identified and investigated. Structural analyses reveal that a lithium amidoborane-ammonia borane complex (LiNH(2)BH(3).NH(3)BH(3)) and two allotropes of lithium amidoborane (denoted as alpha- and beta-LiNH(2)BH(3), both of which adopt orthorhombic symmetry) were formed in the process of synthesis. LiNH(2)BH(3).NH(3)BH(3) is the intermediate of the synthesis and adopts a monoclinic structure that features layered LiNH(2)BH(3) and NH(3)BH(3) molecules and contains both ionic and dihydrogen bonds. Unlike alpha-LiNH(2)BH(3), the units of the beta phase have two distinct Li(+) and [NH(2)BH(3)](-) environments. beta-LiNH(2)BH(3) can only be observed in energetic ball milling and transforms to alpha-LiNH(2)BH(3) upon extended milling. Both allotropes of LiNH(2)BH(3) exhibit similar thermal decomposition behavior, with 10.8 wt % H(2) released when heated to 180 degrees C; in contrast, LiNH(2)BH(3).NH(3)BH(3) releases approximately 14.3 wt % H(2) under the same conditions.

Growth of Crystalline Polyaminoborane through Catalytic Dehydrogenation of Ammonia Borane on FeB Nanoalloy

CAS [KGCX2-YW-806, KJCX2-YW-H21, 2009AA05Z108, 2010CB631304]; US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]

Synthesis of N-doped hierarchical carbon spheres for CO2 capture and supercapacitors

N-doped hierarchical carbon spheres have been synthesized via a soft template and hydrothermal method using melamine as a nitrogen source. The obtained carbon spheres possess a high nitrogen content and well-developed porosity. These carbon spheres are examined as absorbents for CO2 capture and as electrode materials for supercapacitors. Due to the high nitrogen content and hierarchical pore size distribution, the carbons show high CO2 uptakes of 2.2–4.4 mmol g−1 at 298 K and 1 bar. Furthermore, we observe that the carbon spheres exhibit excellent performance as supercapacitor electrodes with a high specific capacitance of 356 F g−1 at a current density of 0.2 A g−1. These carbon spheres as promising materials will exhibit excellent performance in various fields.

N-Doped carbon supported Co3O4 nanoparticles as an advanced electrocatalyst for the oxygen reduction reaction in Al–air batteries

Low-cost and high-performance catalysts are highly desirable for the oxygen reduction reaction (ORR) in metal–air batteries. Herein, a Co3O4/N-doped Ketjenblack (Co3O4/N-KB) composite is proposed as a high performance catalyst for Al–air batteries. The synergistic effect between Co3O4 and N-KB enables the Co3O4/N-KB composite to have a much higher cathodic current, a much more positive half-wave potential and more electron transfer in comparison with Co3O4 or N-KB alone. The Co3O4/N-KB composite favors a direct four electron pathway in the ORR process, and its ORR current density even outperforms the commercial Pt/C (20 wt%). Al–air batteries using the as-prepared catalyst in the air electrode were constructed, which displayed a high discharge voltage plateau of ∼1.52 V, comparable to that of the commercial Pt/C. The developed Co3O4/N-KB composite here could meet the requirements of large-scale application of metal–air batteries due to the much cheaper cobalt source and more economically commercialized carbon source compared to the commercial Pt/C.

Fabrication and characterization of a novel nanoporous Co–Ni–W–B catalyst for rapid hydrogen generation

A highly active nanoporous Co–Ni–W–B alloy has been prepared using chemical reduction in an ethanol solution and tested as a novel catalyst for hydrolysis of ammonia borane. Compared with the alloy prepared in an aqueous solution, the as-prepared alloy shows a much higher surface area and hydrogen generation rate.

Metathesis of alkali-metal amidoborane and FeCl3 in THF

Metathesis of LiNH2BH3 and FeCl3 in THF solution was investigated in detail. Instead of formation of expected Fe amidoborane i.e., 3LiNH2BH3 + FeCl3 → 3LiCl + Fe(NH2BH3)3, 1.5 equiv. H2/LiNH2BH3 together with LiCl and a black precipitate was produced as a result of salt metathesis and reduction of Fe3+ by BH3. The hydrogen was desorbed in two steps involving a homogeneous interaction of the two starting chemicals to form [Fe(H2NBH2)3] precipitate and subsequent solid-state dissociation of [Fe(H2NBH2)3] to yield a polymeric product, [Fe(HNBH)3]n, respectively. FTIR evidenced the persistence of B–H and N–H stretches in the above two solid products and following the dissociation of [Fe(H2NBH2)3] to release 1 equiv. H2/LiNH2BH3 the B–N bond strengthened. Mossbauer and XAFS both indicated that Fe atoms in these solids are in very similar chemical environments, linking to the neighbouring N and B atoms and bearing slightly positive charge. Most likely, H2NBH2 in [Fe(H2NBH2)3] binds to Fe as a π-bound ligand. The mechanism of salt metathesis and reduction of Fe3+ was confirmed based on simulation work on the homogeneous reaction process.

Synthesis of three-dimensional graphene aerogel encapsulated n-octadecane for enhancing phase-change behavior and thermal conductivity

We prepared a series of three-dimensional graphene aerogel (3D-GA) encapsulated n-octadecane (OD) composite phase change materials (PCMs) through both solution and vacuum impregnation to ensure that a homogeneous dispersion of OD in the porous structure of 3D-GA was present. At the same time, we also investigated the micro-structure, thermal storage properties, and thermal conductivity of the composite PCMs. We used scanning electron microscopy and Fourier transform infrared spectroscopy to demonstrate that OD was encapsulated effectively in the porous structure of 3D-GA and that the composite PCMs were prepared successfully. Differential scanning calorimetry (DSC) results confirmed that the composite PCMs possess good phase change behavior, fast thermal-response rates and excellent thermal cycling stability. The melting enthalpy and crystallization enthalpy can reach 195.70 J g−1 and 196.67 J g−1, respectively, and have almost no change for 60 DSC thermal cycles. Temperature–time curves suggested that the composite PCMs have excellent thermal regulation properties, and their temperature can be maintained in the range of 21–27 °C for about 640 s in a heating procedure. Thermal conductivity analysis indicated that the thermal conductivities of the composite PCMs are improved significantly by the highly thermally conductive 3D-GA. All these results demonstrated that the composite PCMs possess good comprehensive properties that can be used widely in energy storage systems.

Simple synthesis of graphene-doped flower-like cobalt–nickel–tungsten–boron oxides with self-oxidation for high-performance supercapacitors

In this study, we devised an easy and simple approach to synthesize a composite of flower-like cobalt–nickel–tungsten–boron oxides (Co–Ni–W–B–O) that were doped with reduced graphene oxide (rGO); the composite was designed for supercapacitor applications. A Co–Ni–W–B alloy was first deposited on rGO through one-pot chemical reduction in an ethanol solution at room temperature. The resulting Co–Ni–W–B alloy self-oxidized in air on the rGO surface. The Co–Ni–W–B–O/rGO composites resembled three-dimensional flowers with a high surface area; they also exhibited superior electrochemical performance when compared to most previously reported electrodes based on nickel–cobalt oxides. Furthermore, the Co–Ni–W–B–O/rGO composite prepared in an ethanol solution showed much higher electrochemical performance than the composite prepared in water. The Co–Ni–W–B–O/rGO electrode showed an ultrahigh specific capacitance of 1189.1 F g−1 at 1 A g−1 and exhibited a high energy density of 49.9 W h kg−1 along with remarkable cycle stability (10 000 cycles with 80.7% capacitance retention at 15 A g−1), which is promising for its application in energy storage devices.

Self-assembly synthesis of nitrogen-doped mesoporous carbons used as high-performance electrode materials in lithium-ion batteries and supercapacitors

Nitrogen-doped mesoporous carbons (NMCs) have been employed as electrode materials for energy storage devices such as lithium-ion batteries (LIBs) and supercapacitors due to their high accessible porosity and nitrogen content. However, how to maintain the structural stability of NMCs with abundant nitrogen atoms in their 2D honeycomb lattice is still a significant challenge. Herein, NMCs with a high nitrogen content of 18.86 wt% have been successfully synthesized via a self-assembly route in the presence of guanine as a nitrogen source. Furthermore, the nitrogen content and porosity of NMCs can be tuned by controlling the experimental conditions. Benefiting from the high N content, appropriate specific surface area (455 m2 g−1), and high accessible porosity, NMC exhibits superior electrochemical performance. This NMC anode for LIBs can retain a discharge capacity as high as 610 mA h g−1 with a coulombic efficiency of 98.5% after 50 cycles. In addition, it also displays good potential towards supercapacitor application with a specific capacitance of 227 F g−1 (in 6 M KOH) at a current density of 0.5 A g−1. The enhanced electrochemical performance could be attributed to both the low charge transfer resistance and the incremental electrochemical activity resulting from the existence of optimized nitrogen atoms.

Organic carbon gel assisted-synthesis of Li1.2Mn0.6Ni0.2O2 for a high-performance cathode material for Li-ion batteries

Lithium-rich layered oxide Li1.2Ni0.2Mn0.6O2 with a stable network flake structure has been synthesized through a facile resorcinol–formaldehyde (RF) organic carbon gel-assisted method. The as-prepared sample used as a cathode material in lithium ion batteries (LIBs) was characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and electrochemical measurements. The stable network flake structure is assembled through a dense stack of nanoparticles with an average size of 50–200 nm. As an active material for LIB cathodes, the Li1.2Ni0.2Mn0.6O2 sample shows excellent rate capacities and cycling stability, and delivers a high initial discharge capacity of 273.3 mA h g−1 at 0.1C (1C = 200 mA g−1) between 2.0 V and 4.8 V. When the discharge rate is increased to 2C, an initial capacity of 196.7 mA h g−1 is obtained. After 150 cycles, a discharge capacity of 183.7 mA h g−1 and a high capacity retention of 93.4% are yielded at a rate of 2C.