YMgGa as a hydrogen storage compound

The hydrogen absorption and desorption properties of the recently found ternary phase YMgGa have been studied. This compound absorbs 2.2 wt% hydrogen during the first cycle, but only 1.1 wt% can be stored reversibly for the following cycles under the applied pressure and temperature conditions. Hydrogen absorption and desorption properties were investigated by measuring the thermal desorption spectra and the pressure-composition isotherms while the crystal structure was determined using X-ray diffraction (XRD). The compound absorbs hydrogen at pressures above 0.2 MPa and 250 °C by decomposing into YH₃ and MgGa. This reaction is reversed when heating the hydride in a He atmosphere; hydrogen is released and the YMgGa phase is partially recovered together with YGa₂ and YH₂. The reformation of YMgGa occurs at temperatures below 450 °C on the expenses of hydrogen desorption from YH₂. This is not expected under these temperature conditions as YH₂ normally does not desorb hydrogen below 800 °C.     

Synthesis and hydrogen storage behavior of Mg-Co-H system at nanometer scale

There are few reports on the hydrogen storage behavior study of Mg-Co-H system in the literature, although Mg₂CoH₅ has a much higher hydrogen capacity than Mg₂NiH₄. This is due to the great difficulty in the synthesis of Mg₂CoH₅ and Mg₂Co in convenient conditions. Here we successfully synthesized the nanostructured Mg₂CoH₅ and Mg₂Co from Mg and Co nanoparticles prepared by hydrogen plasma-metal reaction method. The reaction mechanism of the synthesis of the Mg-Co-H system was studied. The morphology of the Mg-Co-H system in nanometer scale was observed. The hydrogen absorption curves and the pressure-composition isotherm (P-C-T) properties of the Mg-Co-H system were studied. The van’t Hoff equations and the formation enthalpies and entropies of the produced Mg₂CoH₅ and Mg₃CoH₅ were obtained. The results were discussed by comparing with the corresponding ones of Mg-Co-H system by other groups and the ones of nanostructured Mg-H and Mg-Ni-H systems by our group.     

Structural and Electronic Properties of Li2Mg(NH)2 for Hydrogen Storage: First-principles Study

The structural and electronic properties of Li₂Mg(NH)₂ for hydrogen storage have been studied by first-principles calculation. The optimal unit cell parameters and the distance of N-H are determined, which are in good agreement with the experimental data. The bulk modules and the energies of zero pressure are obtained by using Murnaghan equation of states. The results show that the α-Li₂Mg(NH)₂ is a ground state configuration. The overlap population analysis shows that the N-Li/Mg ionic characteristics and N-H interaction of αphase are weaker than those of βphase. The valence band is dominated by the presence of N s and p states, hybridized with the H s state.     

High-capacity hydrogen storage of magnesium-decorated boron fullerene

By theoretical analysis, we have explored the feasibility of functionalizing boron fullerene (B₈₀) by adsorbing Mg atoms for the application as hydrogen storage nanomaterials. Our results show that due to the charge transfer from Mg to B atoms Mg atoms reside above the pentagonal faces of the B₈₀ cage. The electric field induced around the positive charged Mg atoms polarizes H₂ molecules, and the resulting binding is strong enough to adsorb H₂ without dissociation. Further calculations indicated that the 12Mg-decorated-B₈₀ has a high hydrogen storage capacity storing up to 96 H₂ molecules with an ideal binding energy of 0.20 eV/H₂ according to the approximation of GGA and 0.5 eV/H₂ according to LDA, corresponding to a hydrogen uptake of 14.2%. This suggested a possible method of engineering new structure for high-capacity hydrogen storage materials with the reversible adsorption and desorption of hydrogen molecules.     

Pressure induced structural phase transition of OsB2: First-principles calculations

Orthorhombic OsB₂ was synthesized at 1000 °C and its compressibility was measured by using the high-pressure X-ray diffraction in a Diacell diamond anvil cell from ambient pressure to 32 GPa [R.W. Cumberland, et al. (2005)]. First-principles calculations were performed to study the possibility of the phase transition of OsB₂. An analysis of the calculated enthalpy shows that orthorhombic OsB₂ can transfer to the hexagonal phase at 10.8 GPa. The calculated results with the quasi-harmonic approximation indicate that this phase transition pressure is little affected by the thermal effect. The calculated phonon band structure shows that the hexagonal P 6₃/mmc structure (high-pressure phase) is stable for OsB₂. We expect the phase transition can be further confirmed by the experimental work.     

A comparative study of particle swarm optimization and its variants for phase stability and equilibrium calculations in multicomponent reactive and non-reactive systems

Particle swarm optimization is a novel evolutionary stochastic global optimization method that has gained popularity in the chemical engineering community. This optimization strategy has been successfully used for several applications including thermodynamic calculations. To the best of our knowledge, the performance of PSO in phase stability and equilibrium calculations for both multicomponent reactive and non-reactive mixtures has not yet been reported. This study introduces the application of particle swarm optimization and several of its variants for solving phase stability and equilibrium problems in multicomponent systems with or without chemical equilibrium. The reliability and efficiency of a number of particle swarm optimization algorithms are tested and compared using multicomponent systems with vapor–liquid and liquid–liquid equilibrium. Our results indicate that the classical particle swarm optimization with constant cognitive and social parameters is a reliable method and offers the best performance for global minimization of the tangent plane distance function and the Gibbs energy function in both reactive and non-reactive systems.     

Probing the structure, stability and hydrogen storage properties of calcium dodecahydro-closo-dodecaborate

Calcium borohydride can reversibly store up to 9.6 wt% hydrogen; however, the material displays poor cyclability, generally associated with the formation of stable intermediate species. In an effort to understand the role of such intermediates on the hydrogen storage properties of Ca(BH₄)₂, calcium dodecahydro-closo-dodecaborate was isolated and characterized by diffraction and spectroscopic techniques. The crystal structure of CaB₁₂H₁₂ was determined from powder XRD data and confirmed by DFT and neutron vibrational spectroscopy studies. Attempts to dehydrogenate/hydrogenate mixtures of CaB₁₂H₁₂ and CaH₂ were made under conditions known to favor partial reversibility in calcium borohydride. However, up to 670 K no notable formation of Ca(BH₄)₂ (during hydrogenation) or CaB₆ (during dehydrogenation) occurred. It was demonstrated that the stability of CaB₁₂H₁₂ can be significantly altered using CaH₂ as a destabilizing agent to favor the hydrogen release.     

First-principles calculations of stability of graphene-like BC_3 monolayer and its high-performance potassium storage

With increasing demand for renewable energy,graphene-like BC_3 monolayer as high performance electrode materials for lithium and sodium batteries are drawing more attention recently.However,its structural stability,potassium storage properties and strain effect on adsorption properties of alkali metal ions have not been reported yet.In this work,phonon spectra,AIMD simulations and elastic constants of graphene-like BC_3 monolayer are investigated.Our results show that graphene-like BC_3 monolayer possesses excellent structural stability and the maximum theoretical potassium storage capacity can reach up to 1653 mAh/g with the corresponding open circuit voltages 0.66 V.Due to potassium atom can be effectively adsorbed at the most energetically favorable h-CC site with obvious charge transfer,making adsorbed graphene-like BC_3 monolayer change from semiconductor to metal which is really good for electrode utilization.Moreover,the migrations potassium atom on the graphene-like BC_3 monolayer is rather fast with the diffusion barriers as low as 0.12 eV,comparing lithium atom with a relatively large diffusion barrier of 0.46 eV.Additionally,the tensile strains applied on the graphene-like BC_3 monolayer have marginal effect on the adsorption and diffusion performances of lithium,sodium and potassium atoms.     

Preparation and hydrogen storage properties of nanostructured Mg2Cu alloy

We successfully synthesized Mg₂Cu alloys from the metal nanoparticles, which are produced from hydrogen plasma-metal reaction method, in two ways. One is under 0.1 MPa argon at 673 K and the other is under 4.0 MPa hydrogen at 673 K. The structure, morphology and reaction mechanism were studied. The hydrogen absorption and the pressure-composition isotherm properties of the obtained Mg₂Cu alloy under hydrogen were studied. The van’t Hoff equation and the formation enthalpy and entropy of the resulting hydride (MgH₂+MgCu₂) were obtained from the equilibrium plateau pressures of the desorption isotherms. Nanostructured Mg₂Cu shows excellent hydrogen storage properties because nanostructured materials have more surface area and more defects, which means more nucleation sites with hydrogen, and smaller particles, which means shorter diffusion distance for hydrogen in the alloys particles.     

First-principles calculations of the Ti-doping effects on layered NaNiO2 cathode materials for advanced Na-ion batteries

The NaNiO₂ structure is a promising cathode material for sodium ion batteries due to its reasonably high capacity (～120 mAh/g), environmental friendliness and the low cost of required raw materials. First-principles calculations have been carried out to study the Ti ions doped NaNi_1-xTi_xO₂ (x = 0, 0.037, 0.056, 0.083 and 0.167) phases. Results show that Ti doping can lead to a higher average intercalation voltage and improved electronic conductivity. The optimized NaNi_0.917Ti_0.083O₂ sample can effectively suppress the volume change of the unit cell by 4% upon full desodiation and an increased ion mobility was found in this sample by nudged elastic band calculation. We suggest that the NaNi_0.917Ti_0.083O₂ cathode could be a promising candidate for Na-ion batteries.     

焙烧温度对复合储氧材料性能的影响

自上世纪80年代初期以来,稀土铈氧化物(CeO2)作为一种储氧材料已在汽车三效催化剂(TWC)中得到了广泛应用。众所周知,CeO2在富氧和富燃条件下有储氧和释放氧的功能,CeO2在缺氧条件下可通过Ce4 转化成Ce3 而释放出氧气,在富氧条件下Ce3 又可氧化成Ce4 而吸收氧,即2CeO2(Ce2O3 1/2     

生物油储存稳定性实验研究

对松木和玉米芯快速热解制取的生物油进行储存稳定性实验,经过储存老化后的生物油黏度增大,水分含量和固体颗粒物含量增加,pH值、热值、密度无明显变化。通过GC-MS对储存前后生物油中主要组分进行定量分析表明,生物油经过储存后,羟基丙酮、乙酸、糠醛等主要组分的含量明显下降,而2-甲氧基苯酚、4-甲基-2-甲氧基-苯酚、4-甲基-苯酚的含量有所上升。核磁共振的碳谱分析表明,经过储存后生物油中甲氧基碳和双氧-烷基碳的含量降低,而芳基碳和不饱和碳的含量增大,生物油的芳香度有所提高。     

Evaluation of repulsive particle swarm method for phase equilibrium and phase stability problems

Phase equilibrium and stability problems are of crucial importance in simulation, design and optimization of several separation processes. Recently, these problems have been solved using minimization of Gibbs free energy, using global optimization techniques. In this paper, repulsive particle swarm (RPS), a recent global optimization technique is explored for the solution of phase stability and phase equilibrium.     

Green laser ablation-based synthesis of functional nanomaterials for generation,storage, and detection of hydrogen

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Ti,Cr, Al和B合金化元素对α-Nb5Si3力学性能和电子结构的影响

采用基于密度泛函理论(DFT)的第一性原理方法,通过比较形成能(E_form)、价电子浓度(VEC)、弹性常数(C_ij)、剪切模量(G)与体模量(B)的比值(G/B)以及派-纳力(τ_P-N)等参量的变化,研究了Ti、Cr、Al和B合金化对D8₁结构的α-Nb₅Si₃结构稳定性和力学性能的影响. 研究表明：合金化元素Ti、Cr、Al和B分别优先占据α-Nb₅Si₃中Nb^4c、Nb^4c、Si^4a和Si^8h位置;添加不同含量合金化元素的α-Nb₅Si₃仍保持稳定的D8₁结构;Ti、Al和B合金化使α-Nb₅Si₃的脆性增加,而随着Cr含量的增加,α-Nb₅Si₃的韧性逐渐增强. 此外,态密度(DOS)和Mulliken布居等电子结构的计算结果表明：Ti、Al和B合金化导致α-Nb₅Si₃脆性增加的主要原因是提高了共价键的强度;而Cr合金化的增韧作用主要来源于共价键数量的减少和强度的削弱,以及更多的反键态被占据.     

First-principles investigations on structural,electronic and elastic properties of BeSe under high pressure

The structural, electronic and elastic properties of BeSe in both B3 and B8 structures have been studied by first-principles calculations within the generalized gradient approximation (GGA). The calculated lattice parameters and bulk modulus of BeSe are in reasonable agreement with previous results. The predicted value of phase transition pressure from B3 to B8 is 50.24 GPa, which is well in line with the experimental data (56 ± 5 GPa). The calculation of the electronic band structure shows that the energy gap is indirect for B3 and B8 phases. Especially, the elastic constants of B8 BeSe under high pressure were studied for the first time. The bulk modulus, shear modulus, compressional and shear wave velocities of B8 BeSe evaluated from elastic constants as a function of pressure were investigated. In addition, Poisson's radio, elastic anisotropy and Debye temperature were analyzed successfully.     

Hydrothermal synthesis and phase stability of Pb stabilized ZrO2 nanoparticles

The Pb doped metastable tetragonal ZrO₂ (t-ZrO₂:Pb) nanoparticles have been successfully synthesized by hydrothermal method. Pb ion doping has great effects on the phases, crystallite sizes and optical band gaps. Systematic structural characterization revealed that the introduction of Pb ion results in lattice expansion. The as-prepared t-ZrO₂:Pb with ca 4–6 nm in size has high specific surface area (>150 m²/g) and narrow particle size distributions. The diffuse reflectance spectra investigated that the band gap shifts from ultraviolet (E_g = 5.19 eV) for pure ZrO₂ to the visible region for t-ZrO₂:Pb and the gap can be effectively adjusted with the content of Pb in nanocrystals. Through thermal treatment, Pb ion doped in ZrO₂ crystals was excluded with increasing temperature. At 800 °C, the three t-ZrO₂:Pb samples of ZPO-2, ZPO-3 and ZPO-4 still contained the pure tetragonal phase, in which Pb content were not reduced to zero, while the transformation from tetragonal to monoclinic phase occurred due to zero Pb content in ZPO-1. The reason to this transformation and stabilized mechanism of Pb ion in ZrO₂ were discussed.     

Synthesis and phase behavior of polyurethanes end-capped with fluorinated phosphatidylcholine head groups

A series of fluorinated phosphatidylcholine polyurethane macromolecular additives were synthesized by solution polymerization using methylenebis(phylene isocyanates)(MDI) and 1,4-butanediol(BDO) as hard segments,a new phoshporycholine,2-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoro-10-(2-hydroxyethoxy)decyloxy) ethyl phosphorycholine (HDFOPC) as end-capper,and four polydiols,poly(tetramethylene glycol)s(PTMG),polydimethylsiloxane(PDMS), poly(1,6-hexyl-1,5-pentylcarbonate)(PHPC) and poly(propylene glycol)(PPG) as soft segments,respectively.The chemical structures of the synthesized polyurethanes were characterized by ~1H-NMR and FTIR.DSC and DMA were employed to study the phase behavior of these novel polyurethanes due to their great influences on the surface properties,and hence their interactions with bio-systems.The results showed that phase separation of the fluorinated phosphatidylcholine end-capped polyurethanes was increased in comparison with that of normal polyurethanes.The effect of fluorinated phosphatidylcholine end-capped groups on the phase behavior was further demonstrated by analyzing the degree of hydrogen-bonding between hard and soft segments.     

Preparation and characterization of ordered porous carbons for increasing hydrogen storage behaviors

We prepared ordered porous carbons (PCs) by using a replication method that had well-organized mesoporous silica as a template with various carbonization temperatures in order to investigate the possibility of energy storage materials. The microstructure and morphologies of the samples are characterized by XRD, TEM, and FT-Raman spectroscopy. N₂ adsorption isotherms are analyzed by the t-plot method, as well as the BET and the H–K method in order to characterize the specific surface area, pore volume, and pore size distribution of the samples, respectively. The capacity of the hydrogen adsorption of the samples is evaluated by BEL-HP at 77 K and 1 bar. From the results, we are able to confirm that the synthesis of the samples can be accurately governed by the carbonization temperature, which is one of the effective parameters for developing the textural properties of the carbon materials, which affects the behaviors of the hydrogen storage.     

First-principles simulations of the electrode|electrolyte interface

We review a direct dynamics method for the simulation of metal|water interfaces. The occupancy of on-top binding sites for water in this model as applied to a (100) surface of ‘copper' is very sensitive to potential. We suggest that this may account for some previously unexplained features of X-ray data on water structure and noble metal|water interfaces. We discuss the problem of statistical fluctuations on the occupancy of such tightly bound water molecules in such simulations. Though the problem is not too serious for charged interfaces, the problem of accounting for fluctuations at zero charge can be quite formidable, as we illustrate for the (100) surface of copper.