Reduction In Hydrogen Capacity Research Articles

Superior Reversible Hydrogen Storage Properties and Mechanism of LiBH4–MgH2–Al Doped with NbF5Additive

LiBH4 is one of the most potential candidates for hydrogen storage materials among several sorts of complex borohydrides. Utilizing reactive hydride composites on LiBH4 could destabilize the thermodynamics and improve dehydrogenation behaviors, such as the excellent reversibility of LiBH4–MgH2 and the fast dehydrogenation of LiBH4–Al. The strategy of combining both outstanding effects of MgH2 and Al to form LiBH4–MgH2–Al system has been proposed. However, reduction of hydrogen capacity during cycles has not been solved for the LiBH4–MgH2–Al system, which is considered as the principal problem. In this work, we investigated the reversible hydrogen storage performance and reaction mechanism of LiBH4–MgH2–Al doped with/without NbF5 additive. It can be found that the dehydrogenation of 4LiBH4–MgH2–Al can release about 9.0 wt % H2 quickly without incubation period, compared with 2LiBH4–MgH2. Moreover, it is the first time to achieve completely reversible hydrogen desorption property of LiBH4–MgH2–Al by doping ...

Effects of tungsten addition on hydrogen absorption and permeation properties of Nb40Ti30Ni30 alloy

Tungsten was added to Nb40Ti30Ni30 alloys to investigate its effects on microstructure, hydrogen permeability and hydrogen absorption properties. Tungsten-added alloys consisted of a primary (Nb, Ti) phase and TiNi+(Nb, Ti) eutectic structure, although tungsten concentrated at the center of the primary phase. Tungsten addition did not change their hydrogen permeability. However, the hydrogen capacity decreased with increasing tungsten content, and 20% reduction of hydrogen capacity was attained by adding 5% tungsten. After annealing, tungsten was dissolved homogeneously in the primary phase, and segregation disappeared. The hydrogen permeability and capacity of the annealed alloy were 50% higher and 10% lower, respectively, than those of tungsten-free alloy. Thus, tungsten can reduce hydrogen capacity without degrading hydrogen permeability, which is expected to improve the resistance to hydrogen embrittlement.

Microstructure and Hydrogen Storage Properties of Ti1V0.9Cr1.1 Alloy with Addition of x wt % Zr (x = 0, 2, 4, 8, and 12)

The effect of adding Zr on microstructure and hydrogen storage properties of BCC Ti1V0.9Cr1.1 synthesized by arc melting was studied. The microstructures of samples with Zr were multiphase with a main BCC phase and secondary Laves phases C15 and C14. The abundance of secondary phases increased with increasing amount of zirconium. We found that addition of Zr greatly enhanced the first hydrogenation kinetics. The addition of 4 wt % of Zr produced fast kinetics and high hydrogen storage capacity. Addition of higher amount of Zr had for effect of decreasing the hydrogen capacity. The reduction in hydrogen capacity might be due to the increased secondary phase abundance. The effect of air exposure was also studied. It was found that, for the sample with 12 wt % of Zr, exposure to the air resulted in appearance of an incubation time in the first hydrogenation and a slight reduction of hydrogen capacity.

Mg-based Nanocomposites for Hydrogen Storage Containing Ti-Cr-V Alloys as Additives

In this study, we have investigated the synthesis, microstructure and hydrogen storage properties of Mg-based nanocomposites containing different concentrations of TiCrV and TiCr1.2V0.8 alloys. The Mg-based nanocomposites of Mg containing Ti-Cr-V additives were prepared by reactive milling (RM) under hydrogen atmosphere. The structural characterization revealed the presence of the β-MgH2, γ-MgH2 and BCC phases in the powders samples after RM. In addition, a very refined and homogenous microstructure with average MgH2 crystallite size of around 10-12 nm was observed, including a nanometric dispersion of the additives in the magnesium hydride matrix. The doping with TiCrV and TiCr1,2V0,8 greatly improves the hydrogen desorption behavior of Mg in comparison with the sample without additive, resulting in the lowest onset temperature (240 oC) for the sample containing 5%mol. of TiCrV. Very fast absorption and desorption kinetics at 275 oC and 300 oC (7 minutes and 5 minutes for full desorption and absorption, respectively) were observed in the samples containing TiCrV and TiCr1,2V0,8 without any notable difference between the type of additive used in comparison with the pure sample. However, a slight reduction in hydrogen capacity is observed in the mixtures than for the pure sample (6.7 wt.% against 7.3 wt.%).

Effects of Substitution of Al and Bi for Ni on Structure and Hydrogen Storage Properties of LaNi4.7-xAl0.3Bix (x=0.1, 0.2, 0.3) Alloy

In this research, the effects of Al and Bi substitution for Ni on the microstructure and hydrogen absorption/desorption properties of LaNi4.7-xAl0.3Bix (x=0.1, 0.2, 0.3) alloys were investigated. The results showed that substituting Ni with Al led to a desirable decrease in absorption/desorption plateau pressure as well as to hysteresis without a reduction in hydrogen capacity. However, Bi substitution reduced the hydrogen capacity and increased the absorption/desorption plateau pressure of the samples. The formation of the (Al,Ni) intermetallic and Bi phases at grain boundaries was found to be the main reason for the changes in hydrogen storage properties.

Effects of Ti-Based Additives on the Hydrogen Storage Properties of aLiBH4/CaH2Destabilized System

The hydrogen storage properties of a destabilizedLiBH4/CaH2system ball-milled withTiCl3,TiF3, andTiO2additives have been investigated. It is found that the system withTiCl3additive has a lower dehydrogenation temperature than the ones with other additives. Further study shows that a higher amount ofTiCl3is more effective in reducing the desorption temperature of theLiBH4/CaH2system, since it leads to a lower activation energy of dehydrogenation. The activations energies for mixtures containing 4, 10, and 25 mol% ofTiCl3are 141, 126, and 110 kJ/mol, respectively. However, the benefits of higher amounts ofTiCl3are offset by a larger reduction in hydrogen capacity of the mixtures.

High-Throughput Synthesis and Screening of Hydrogen-Storage Alloys

Libraries of mixed-metal hydride materials are synthesized on a silicon microfabricated array of "hot-plate" MEMS devices, which allow high-throughput screening using temperature programmed desorption and infrared thermography. The heating plate of the MEMS device is a membrane with low heat capacity, allowing fast and localized temperature control and the extraction of calorimetric data from thermography. The combination of the synthetic method and screening chip allows a fast determination of the desorption temperature and hydrogen content of the materials. Mixed metal hydrides are synthesized directly. The potential of the method is exemplified by presenting results for the sorption properties of Mg xNi 1- x hydride thin-film materials. The results are consistent with the literature, showing the highest hydrogen capacity and desorption temperature for the MgH 2 phase in Mg-rich compositions and the promotion of a lower temperature desorption from the Mg 2NiH 4 phase, with a concomitant reduction in hydrogen capacity.

Hydrogen sorption performance of pure magnesium during continued cycling

Preliminary investigations of the hydrogen absorption - desorption by commercially pure magnesium powder under continuous operation show little or no reduction in hydrogen capacity up to 70 cycles and high temperature exposure exceeding 1200 h. Absorption was studied at 260°–425°C and hydrogen pressures up to 2.0 MPa above equilibrium. Desorption was with a few exceptions done at 400°C at hydrogen pressures below 150 kPa. For practical application the hydrogen exchange may be limited to 75–90% of the complete metal to stoichiometric hydride reaction. A change of the macroscopic structure of the powder into a highly porous, sintered agglomerate did not reduce the hydrogen capacity or the reaction rate. Although this change in structure caused no deterioration of the cycling performance a further development may not be acceptable. For observation over a much larger number of cyclings a fully automated, triple line cycling facility permitting simultaneous testing under different conditions has been constructed.