Papers by Keyword: Hydrogen Storage

Abstract: In this research, AZ31 and AZ91 magnesium alloys were used as hydrogen storage materials to compare the effects of equal channel angular pressing (ECAP) and high energy ball milling (HEBM) processes on the hydrogen storage properties. In addition, the effects of using different AZ magnesium alloys (AZ31 and AZ91) with the same processes and parameters on the hydrogen storage properties were investigated. The results show that the crystal size of AZ magnesium alloy has been decreased by both ECAP and HEBM processes. It was also revealed that AZ31 magnesium alloy processed by ECAP route B_C with 8 passes has faster absorption and desorption rate than AZ31 magnesium alloy processed by HEBM ball material ratio 30:1 with 300rpm. The capacity of two samples is 7.0 and 6.8 wt.%. The AZ91 magnesium alloy processed by HEBM ball material ratio 30:1 with 300rpm has faster hydrogen absorption and desorption rate than that of AZ91 magnesium alloy processed by ECAP route B_C with 8 passes at 375^oc. The capacity of two samples is both 6.7 wt.%.

Abstract: From first principles density functional theory, Li-decorated octagraphene and its usage as a hydrogen storage media is theoretically investigated. Octagraphene is a versatile structure with periodic sp² – bonded carbon atomic planar sheet. This carbon allotrope consists of carbon octagons and rectangular lattices with two bond lengths. The Li binding energy in octagraphene is 2.5 eV, which is much higher than that of pristine graphene. Maximum of four hydrogen molecules can be adsorbed on Li decorated on one side of octagraphene and this leads to a gravimetric storage capacity of 2.4 wt% with an average adsorption binding energy of 0.35eV/H2. Li decorated on both sides of octagraphene, attains a gravimetric storage capacity of 8.1 wt% with an average binding energy of 0.23 eV/ H2. Thus, the structure investigated here is flattering for the reversible hydrogen adsorption/ desorption at the room temperature.

Abstract: Hydrous hydrazine is a promising hydrogen carrier material because of its high content of hydrogen (8.0 wt.%) and easy recharging as a liquid. Amorphous Ni_8.1Co_1.0Pt_0.9/Ce₂O₃ nanoparticles with low precious-metal content were synthesized by a facile co-reduction method at room temperature under ambient atmosphere. The increased degree of amorphization was attributed to the introduction of Ce₂O₃. The resultant Ni_8.1Co_1.0Pt_0.9/Ce₂O₃ nanocomposite was employed as an efficient nanocatalyst towards the decomposition of hydrous hydrazine to H₂, and exhibited excellent catalytic activity and 100% H₂ selectivity. Turnover frequency (TOF) value catalyzed by amorphous Ni_8.1Co_1.0Pt_0.9/Ce₂O₃ is 93.75 h^-1, which is much higher than Ni_8.1Co_1.0Pt_0.9 (4.39 h^-1) at 298 K. The development of the improved catalytic performance and low-cost catalyst with amorphous structure is believed to strongly promote the practical application of hydrous hydrazine as a hydrogen storage material.

Abstract: Metal-organic frameworks (MOFs: MIL-125)-graphene oxide (GO) composite (MO) was synthesized by solvothermal method. All the materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. Then their hydrogen storage properties were systematically tested under 1 bar and 77K. The composite material MO-1 possesses higher surface area than the parent material MIL-125 and shows a remarkable H₂ capacity up to 2.5 wt% (38% increases vs. MIL-125).

Abstract: We have studied the diffusive mobility of hydrogen molecules confined in different size cages in clathrate hydrates. In clathrate hydrate H₂ molecules are effectively stored by confinement in two different size cages of the nanoporous host structure with accessible volumes of about 0.50 and 0.67 nm diameters, respectively. For the processes of sorption and desorption of the stored hydrogen the diffusive mobility of the molecules plays a fundamental role. In the present study we have focused on the dynamics of the H₂ molecules inside the cages as one aspect of global guest molecule mobility across the crystalline host structure. We have found that for the two cage sizes different in diameter by only 34 % and in volume by about a factor of 2.4, the dimension can modify the diffusive mobility of confined hydrogen in both directions, i.e. reducing and surprisingly enhancing mobility compared to the bulk at the same temperature. In the smaller cages of clathrate hydrates hydrogen molecules are localized in the center of the cages even at temperatures >100 K. Confinement in the large cages leads to the onset already at T=10 K of jump diffusion between sorption sites separated from each other by about 2.9 Å at the 4 corners of a tetrahedron. At this temperature bulk hydrogen is frozen at ambient pressure and shows no molecular mobility on the same time scale. A particular feature of this diffusive mobility is the pronounced dynamic heterogeneity: only a temperature dependent fraction of the H₂ molecules was found mobile on the time scale covered by the neutron spectrometer used. The differences in microscopic dynamics inside the cages of two different sizes can help to explain the differences in the parameters of macroscopic mobility: trapping of hydrogen molecules in smaller pores matching the molecule size can to play a role in the higher desorption temperature for the small cages.

Abstract: As hydrogen generation technologies using renewable energy sources are being developed, considerable attention is paid to storage and transportation of hydrogen gas. Metal hydride alloys are considered as promising materials because they are viewed as an attractive alternative to conventional hydrogen storage cylinders and mechanical hydrogen compressors. Compared to storing in a classic gas cylinder, which requires compression of hydrogen at high pressures, metal hydride alloys can store the same amount of hydrogen at nearly room pressure. However, this hydrogen absorption necessitates an effective way to reject the heat released from the exothermic hydriding reaction. In this paper, fin structures are employed to enhance the heat transfer of metal hydride alloys in a cylindrical reactor. Numerical simulations are performed based on a multiple-physics modeling to analyze the transient heat transfer during the hydrogen absorption process. The objective is to minimize the time elapsed for the process and to reduce the hotspot temperature by determining the number and shape of rectangular fins while the total volume of fins used are fixed. The simulation results show that the more fins are applied the better heat transfer is achieved and that there exists an optimal length of the fins.

Abstract: Liquid organic hydrogen carriers (LOHC) are a promising form to store hydrogen. However, the process of dehydrogenation has to be demonstrated for applications with proton exchange membrane (PEM) fuel cells which require very pure hydrogen. Here we document the measured degradation effects due to CO contamination on a PEM fuel cell that is supplied with hydrogen from a LOHC and we want to use later in a maritime application.

Abstract: Metal-organic frameworks (MOFs: copper containing CuBTC)-graphene oxide (GO) composite (CG) was synthesized using microwave heating. The parent material and the composite were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), nitrogen sorption, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (HRTEM) and Raman spectroscopy. Then their hydrogen storage properties were systematically tested. The composite material CG shows a remarkable H₂ capacity up to 2.43 wt% (28.6% increases vs. CuBTC) and higher surface area and pore volume compared to the neat CuBTC. And the particle size of CG is down to nanometer scale.

Abstract: The AlCl₃/Ti co-doped 4MgH₂-Li₃AlH₆ has been successfully synthesized using solid ball-milled method. The effect of AlCl₃/Ti and different preparation conditions on reversible hydrogen storage of 4MgH₂-Li₃AlH₆ were investigated. It was found that the formed Al₃Ti and Al can improve the de/rehydriding performance. The onset temperature of the system dehydrogenation decreased to 58 °C, and it can release hydrogen of 7.2 wt.% at 400 °C. The hydriding of the system was found that the adsorption rate greatly increased from 0.02 to 0.35 wt.% min^-1. The activation energy (E_a) of MgH₂ dehydrogenation decreased from 147 to 113.7 kJ mol^-1 by adding additive AlCl₃ and Ti. The AlCl₃/Ti improved the thermodynamic and kinetic performance of the 4MgH₂-Li₃AlH₆ composite, which was attributed to the high catalytic activity of Al₃Ti and Al.

Abstract: The nitrogen-doped mesoporous carbon spheres have been synthesized via soft-template and hydrothermal synthetic strategies using phenol/formaldehyde resins as carbon sources and melamine as a nitrogen source. The obtained carbon spheres exhibit a spherical morphology with a size range of 3-5 μm, which possess the narrow microporosity (ca. 1.2 nm) and mesoporosity (ca. 4 nm), large surface area (560-1200 m² g^-1) and high nitrogen contents (up to 15.7 wt%). Due to the well-developed porous structure and high nitrogen content, the carbon spheres show high performance for hydrogen storage, and the hydrogen adsorption capacities are in the range of 140-185 cm³ g^-1, which is better than that of most activated carbons. The incorporation of nitrogen into carbons is favored for hydrogen uptake in low pressure.