Papers by Keyword: Hydrogen Storage

Abstract: The geometrical structures of platinum atoms adsorbed on graphene were optimized using plane wave pseudopotential method with generalized gradient approximation based upon the density functional theory. Adsorption energies of both intrinsic graphene and platinum atoms adsorbed on graphene were calculated theoretically. The results show that: Compared with the intrinsic, H2 molecules are strongly adsorbed onto the platinum atoms adsorbed on graphene with higher adsorbed energy. The difference between the highest hydrogen molecule occupied molecular orbital and the 1owest unoccupied molecular orbital is significantly reduced. Between hydrogen and other atoms, the charge transfers are apparent increased. All are help for hydrogen storage.

Abstract: Magnesium is light, abundant and it can store up to 7.6 wt. % of hydrogen forming MgH₂ and accordingly it is a promising material for hydrogen storage. Processing of Mg-based mixtures by high-energy ball milling (HEBM) can produce materials with high level H-sorption properties. In the present report, we display and compare the effects of different nanocrystalline additives (MgF₂, Fe, NbH_0,89, FeF₃, VF₃) on the formation of MgH₂ by reactive milling. The H-desorption behavior of the as-prepared nanocomposites is also evaluated. A combined catalytic effect is observed due to the synergic action of MgF₂ and Fe (or NbH_0,89) on the hydrogenation rate during processing. The transition metal fluorides promote as well the MgH₂ synthesis. By using more energy-intensive milling conditions and adequate additives in given proportions (e.g. 5 mol. % FeF₃), is shown to be very effective for a full and fast synthesis (4 h) of MgH₂ by reactive milling.

Abstract: We synthesized ceramic-type Mg₂Ni alloys (hydrogen storage alloy) by sintering at high temperature in Ar atmosphere and applied the sintered materials to the anode of the metal hydride batteries. As a result, it was found that the samples were obtained as sintered alloys, mainly composed of hexagonal phase with a little MgO. The discharge capacity of the sintered sample was more than 150 mAhg^-1 on the 1st cycle. It decreased to lower than 50 mAhg^-1 after a few cycles, but the capacity was maintained over 20 cycles. The cycling capacity retention is due to the packed fusion of the alloy particles by sintering, which denotes a good effect of sintering method to prepare alloy materials.

Abstract: Ammonia borane (AB) hydrides have been employed as disposable hydrogen (H2) sources for fuel cell applications, due to their high hydrogen capacity. In this paper, ammonia borane (AB) complex with high purity was synthesized by chemical method, using the low cost raw materials of NaBH4, CO2, and NH3. The thermal dynamic for the synthesis process is analyzed. The phase composition for the obtained ammonia borane (AB) complex powders was detected by X-ray diffraction (XRD) characterization. The results suggest that, very high purity ammonia borane (AB) complex powders were obtained, which was quite in agreement with the standard index of ammonia borane.

Abstract: This work presents a first-principles molecular dynamics study of hydrogen storage in Li doped single-wall carbon nanotubes (SWCNTs). The decomposition and adsorption between Li atom and H2 molecular are studied by bonds analysis and energy evolvement of interaction process. The modify effects of Li doped SWCNTs are studied by band structure and of states density analysis, as well as the structure transformation of SWCNTs. The enhanced hydrogen storage in Li doped SWCNTs at room temperature and common pressure is studied by first principles molecular dynamics simulation. The relationship between dope position of Li atoms and hydrogen storage also studied, and finally confirm the best dope position and provide a reference for the further research of alkali metals doped CNT.

Abstract: Hydrogen is considered a promising alternative energy carrier that can potentially facilitate the transition from fossil fuels to sources of clean energy because of its prominent advantages such as high energy density, great variety of potential sources, light weight and low environmental impact (water is the sole combustion product). Due to low price and abundance magnesium should be considered as a potential candidate for hydrogen storage. Recent progress in the application of Magnesium-based nanostructured and composite materials in hydrogen storage is presented in this review. The main focus is on the synthesis of composite material, the design of nanocomposite material, the improvement of the thermodynamical properties and kinetics of hydrogenation/dehydrogenation and the improvement of resistance towards oxygen contamination.

Abstract: In recent years, solid clathrate gas hydrates are considered to be promising materials for hydrogen storage because they can trap molecular hydrogen within their cages formed by a hydrogen-bond water network. In this paper, we firstly synthesized the nitrogen hydrates, and then used these hydrates for hydrogen storage. The H₂ storage potential in these hydrates is investigated by Raman spectrometry technique. The spectral properties show that the multiple H₂ occupancies of large cages of N₂ hydrates have been realized under mild condition (16 MPa and 255 K) when exposing N₂ hydrates in pressurized H2 gas. The results suggest that nitrogen clathrate hydrates are prospective media for H₂ storage and may help to design and produce new hydrogen storage materials.

Abstract: An overview of recent advances in hydrogen storage is presented in this review. The main focus is on metal hydrides, liquid-phase hydrogen storage material, alkaline earth metal NC/polymer composites and lithium borohydride ammoniate. Boron-nitrogen-based liquid-phase hydrogen storage material is a liquid under ambient conditions, air- and moisture-stable, recyclable and releases H₂ controllably and cleanly. It is not a solid material. It is easy storage and transport. The development of a liquid-phase hydrogen storage material has the potential to take advantage of the existing liquid-based distribution infrastructure. An air-stable composite material that consists of metallic Mg nanocrystals (NCs) in a gas-barrier polymer matrix that enables both the storage of a high density of hydrogen and rapid kinetics (loading in <30 min at 200°C). Moreover, nanostructuring of Mg provides rapid storage kinetics without using expensive heavy-metal catalysts. The Co-catalyzed lithium borohydride ammoniate, Li(NH3)4/3BH4 releases 17.8 wt% of hydrogen in the temperature range of 135 to 250 °C in a closed vessel. This is the maximum amount of dehydrogenation in all reports. These will reduce economy cost of the global transition from fossil fuels to hydrogen energy.

Abstract: The isosteric heat of adsorption was used to study the interaction between hydrogen molecules and the Multi-Walled Carbon Nanotubes (MWCNTs). Characterizations of the MWCNTs sample were carried out based on the N2 adsorption isotherm at 77 K and the images from TEM and HRTEM. Step by step method was used to volumetrically measure hydrogen adsorption isotherms at equilibrium temperature-pressures from 123-310 K and 0-12.3 MPa. Isosteric heats of adsorption at seven excess adsorption amounts and that at zero surface loading were respectively determined by the slopes of the adsorption isosteres and the plot of the temperature dependence of the Henry’s constants. Results show that the limit of the isosteric heat of adsorption at zero surface loading is about and the mean under the experimental condition is about . The values are in the same grade as those of hydrogen on the activated coconut charcoal but smaller than those of hydrogen on the graphitized carbon black P33, the activated carbon AX-21 and the Single-Walled Carbon Nanotubes (SWCNTs). Conclusions are drawn that relatively lower adsorption amounts and the isosteric heat of hydrogen adsorption on the MWCNTs could be ascribed to the small specific surface area and the large mesopores.

Abstract: The effect of annealing treatment on the structure, gaseous hydrogen characteristics and electrochemical properties of the La _0.67 Mg _0.33 Ni _2.5 Co _0.5 alloys was investigated. Alloy structure analyses show that all of the alloys consisted of complex phases such as (La,Mg)₂(Ni,Co)₇ phase, (La,Mg)(Ni,Co)₃ phase and La(Ni,Co)₅ phase. The homogenization of composition was improved by annealing treatment. Gaseous hydrogen characteristics were also improved after annealing. The pulverization of the alloy particles was reduced after annealing treatment, which could improve the cycling stability. Electrochemical experiments show that all of the alloy electrodes exhibited good activation characteristics, that annealing treatment improved the maximum discharge capacities of the alloy electrodes from 371.1 mAh/g (as-cast) to 387.7 mAh/g (1173K). The cyclic stability of alloy electrodes was also improved after annealing. However, the high rate dischargeability characteristics were deteriorated.