Junzhi Yang

In situ hybridization of LiNH2–LiH–Mg(BH4)2 nano-composites: intermediate and optimized hydrogenation properties

Nano-composites of LiNH(2)-LiH-xMg(BH(4))(2) (0 ≤ x ≤ 2) were prepared by plasma metal reaction followed by a nucleation growth method. Highly reactive LiNH(2)-LiH hollow nanoparticles offered a favorable nucleus during a precipitation process of liquid Mg(BH(4))(2)·OEt(2). The electron microscopy results suggested that more than 90% of the obtained nano-composites were in the range 200-400 nm. Because of the short diffusion distance and ternary mixture self-catalyzing effect, this material possesses enhanced hydrogen (de)sorption attributes, including facile low-temperature kinetics, impure gases attenuation and partial reversibility. The optimal hydrogen storage properties were found at the composition of LiNH(2)-LiH-0.5Mg(BH(4))(2), which was tentatively attributed to a Li(4)(NH(2))(2)(BH(4))(2) intermediate. 5.3 wt% hydrogen desorption could be recorded at 150 °C, with the first 2.2 wt% release being reversible. This work suggests that controlled in situ hybridization combined with formula optimization can improve hydrogen storage properties.

Excellent hydrogen sorption kinetics of thick Mg–Pd films under mild conditions by tailoring their structures

500 nm thick Mg–Pd films with different structures were prepared and their hydrogen storage properties were investigated. Results indicated that thin Ti interlayers in the Mg bulk film could significantly improve the hydrogen sorption kinetics and reversibility, offering an effective way to improve the hydrogen storage properties of thick Mg-based films.

Two pillared-layer metal–organic frameworks constructed with Co(II), 1,2,4,5-benzenetetracarboxylate, and 4,4′-bipyridine: syntheses, crystal structures, and gas adsorption properties

Two new metal–organic frameworks (MOFs) [Co2(btec)(bipy)2(DMF)]·DMF·3H2O (1) (btec = 1,2,4,5-benzenetetracarboxylate; bipy = 4,4′-bipyridine; DMF = N,N′-dimethylformamide) and Co2(btec)(bipy)(DMF)2 (2) were synthesized with the same starting materials under different solvothermal conditions. The higher temperature favors the generation of compound 2, while the slightly lower temperature with the higher bipy ratio leads to the porous structure of compound 1. Their structures are determined by single-crystal X-ray diffractions. Compound 1 is a 3D pillared-layer framework with interconnected channels along two directions after the removal of free guest molecules. The BET (Brunauer–Emmett–Teller) surface area of 1 was calculated to be 596 m2 g−1 by nitrogen adsorption at 77 K. The hydrogen adsorption isotherm at 77 K shows an excess uptake of 1.1 wt% at 15 bar. The heat (Qst) of hydrogen adsorption was estimated to be 7.3 kJ mol−1 at zero coverage. In compound 2, the wave-like layers constructed with btec are further pillared by bipy, giving rise to the 3D framework with the 1D channels occupied by coordinated DMF molecules.

Preparation and Dehydrogenation Properties of Lithium Hydrazidobis(borane) (LiNH(BH3)NH2BH3)

LiNH(BH3)NH2BH3, the first example of metal-substituted hydrazine bisborane (HBB), is synthesized via the reaction between HBB and n-butyllithium in ether solution. (11)B NMR and Fourier transform infrared spectroscopy indicate a new structure, in which one of the N-H bonds is replaced by a N-Li bond. The X-ray diffraction pattern of the product also indicates the formation of a new crystal structure. This compound releases hydrogen at 126 and 170 °C with satisfactory purity and exhibits superior hydrogen storage properties compared with HBB. Differential scanning calorimetry measurement suggests the dehydrogenation reaction of this compound is less exothermic than that of HBB.

Thickness induced uniaxial anisotropy and unexpected four-fold symmetry in Co/SiO2/Si films

Co films with thickness ranging from 20 to 160 nm have been fabricated on SiO2/Si substrates by pulsed laser deposition method (PLD). It was found that that the Co crystal tends to have a structure of bulk hcp Co with the increase of the Co film thickness, and the coercivity of the Co film decreases with increasing film thickness due to the change of the grain size. A uniaxial anisotropy was found in Co films with thickness less than 120 nm, while the Co films with thickness more than 120 nm show an unexpected four-fold anisotropy which is ascribed to the existence of two types (directions) of strongly exchange-coupled hcp Co grains.

Magnetic properties of Nd(Fe1-xCox)10.5M1.5 (M=Mo and V) and their nitrides

In this work, alloys of Nd(Fe1-xCox)10.5M1.5 (M=Mo and V) were prepared via arc melting and heat treatment. The nitrides of these alloys were synthesized using a gas-solid state reaction method. The influence of Co substitution for Fe in NdFe10.5Mo1.5 and NdFe10.5V1.5 alloys and their nitrides were investigated. It was found that the lattice parameters a, c, and unit cell volume V decrease with increasing Co content x for Nd(Fe1-xCox)10.5Mo1.5. As compared to their parent alloys, the lattice parameters and unit cells volume increase after nitrogenation, which gives rise to higher Curie temperature, magnetization and magnetocrystalline anisotropy field for nitrides. A small amount of Co substitution for Fe (x≤0.3) can enhance the magnetic properties including Curie temperature, saturation magnetization and magnetocrystalline anisotropy field of the alloys and their nitrides, while higher concentration of Co (x>0.3) will deteriorates these magnetic properties, especially for the nitrides, due to the modific...

Tunnel-structured Na(0.54)Mn(0.50)Ti(0.51)O2 and Na(0.54)Mn(0.50)Ti(0.51)O2/C nanorods as advanced cathode materials for sodium-ion batteries.

Tunnel-structured Na(0.54)Mn(0.50)Ti(0.51)O2 nanorods have been synthesized by a facile molten salt method. These nanorods are grown in the direction normal to the sodium-ion tunnels, greatly shortening the diffusion distance of sodium ions and benefiting the transfer kinetics. Thus, the nanorods show significant enhancements in terms of reversible capacity, cycling stability and rate capability. The electrochemical performance could be further promoted via carbon coating to ∼122 mA h g(-1) after 150 cycles at 0.2 C or ∼85 mA h g(-1) after 400 cycles at 1 C.