Hydrogen Desorption Temperature Research Articles

Nanoconfinement of borohydrides in hollow carbon spheres: Melt infiltration versus solvent impregnation for enhanced hydrogen storage

Nanoconfinement of complex hydrides and in particular borohydrides has appeared as a powerful method to modify the hydrogen storage properties of hydrides. However, the improvements obtained strongly depend upon the synthetic method. Herein, we assessed the effectiveness of melt infiltration and solvent impregnation under the same experimental conditions and with a porous carbon, to enable an effective nanoconfinement of borohydrides and further release of hydrogen at low temperatures. Owing to the different wetting conditions of borohydrides at the carbon surface, solvent impregnation was found to lead to the lowest hydrogen desorption temperatures with a desorption temperature as low as 100 °C achieved for nanoconfined LiBH4 and Mg(BH4)2. In this case, some reversibility of the hydrogen release was also observed at 300 °C under 6 MPa. In contrast, melt infiltration led to higher hydrogen desorption temperatures (>300 °C) owing to the difficulty of better confining the molten hydrides within the carbon porosity and no hydrogen reversibility was observed. The improvements in the hydrogen storage properties of borohydrides is thus extremely sensitive to the synthetic conditions (e.g. temperature) and this point toward the need of better approaches to enable the control of the properties of complex hydrides at the nanoscale.

The Influence of Size and Shape of Pd Nanoparticles on the Performances of Pd/Beta Catalysts for n‐Heptane Hydroisomerization

AbstractSeveral Pd/Beta catalysts with cubic (9 nm, 12 nm, 16 nm) and truncated‐octahedral (18 nm) Pd nanoparticles (NPs) were prepared to investigate the effect of size and shape of Pd NPs for n‐heptane hydroisomerization. Characterizations confirmed that the cubic Pd NPs solely exposed {100} crystal plane and truncated‐octahedral Pd NPs were enclosed by {100} and {111} crystal planes, and that the desorption temperature of subsurface hydrogen on Pd NPs showed size and shape dependence. Hydroisomerization results exhibits that the catalyst with 9 nm cubic Pd NPs displayed the higher isomers selectivity compared to the catalyst with 12 nm cubic NPs, 18 nm truncated octahedral NPs and 16 nm cubic NPs at similar conversion. This result suggested the size and shape dependence of (de)hydrogenation activity of Pd NPs, and further revealed the key role of subsurface hydrogen in determining the (de)hydrogenation activity.

Significant Thermodynamic Destabilization and Superior Hydrogen Storage Properties of Nanocrystalline Mg-20 wt % Ti–Cr–Vx (x = 0.4, 0.6, 0.8; Ti/Cr = 2:3) Composites Synthesized by Reactive Ball Milling

Nanocrystalline Mg-20 wt % Ti–Cr–Vx (x = 0.4, 0.6, 0.8; Ti/Cr = 2:3) composites were synthesized by reactive ball milling of Mg and Ti–Cr–Vx powders for 8 h under 5.0 MPa H2 at room temperature. The morphology, crystal structure, and isothermal hydrogen ab-/desorption properties of the materials were investigated. The as-synthesized nanocomposites comprise β-MgH2, γ-MgH2, and Ti–Cr–Vx–Hy (1.88 < y < 1.92) as confirmed by X-ray diffraction analysis. High-resolution transmission electron microscopy images show that both β-MgH2 and γ-MgH2 co-existed in a single nanocrystalline. Differential scanning calorimetry results reveal that Mg-20 wt % Ti0.16Cr0.24V0.6 powders possess the lowest hydrogen desorption temperature at 224 °C with the apparent activation energy of 76.32 kJ/mol for dehydrogenation. The nanocrystalline Mg-20 wt % Ti0.16Cr0.24V0.6 powders exhibit excellent dehydrogenation kinetics. They can desorb 5.67 wt % H2 in 20 min at 270 °C under 0.01 MPa H2 pressure, compared with only 0.10 wt % H2 for a...

Counting electrons - A new approach to tailor the hydrogen sorption properties of high-entropy alloys

We have investigated the structure and hydrogen storage properties of a series of quaternary and quintary high-entropy alloys related to the ternary system TiVNb with powder X-ray diffraction (PXD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and manometric measurements in a Sieverts apparatus. The alloys have body-centred cubic (bcc) crystal structures and form face-centred cubic (fcc) metal hydrides with hydrogen-to-metal ratios close to 2 by hydrogenation. The onset temperature for hydrogen desorption, Tonset, decreases linearly with the valence-electron concentration, VEC. Moreover, the volumetric expansion per metal atom from the bcc alloys to the fcc hydrides, [(V/Z)fcc−(V/Z)bcc]/(V/Z)bcc, increases linearly with the VEC. Therefore, it seems that a larger expansion of the lattice destabilizes the metal hydrides and that this effect can be tuned by altering the VEC. Kissinger analyses performed on the DSC measurements indicate that the destabilization is a thermodynamic rather than kinetic effect.Based upon these insights we have identified TiVCrNbH8 as a material with suitable thermodynamics for hydrogen storage in the solid state. This HEA-based hydride has a reversible hydrogen storage capacity of 1.96 wt% H at room temperature and moderate H2-pressures. Moreover, it is not dependent on any elaborate activation procedure to absorb hydrogen.

First-principles study of Pd single-atom catalysis to hydrogen desorption reactions on MgH2(110) surface

MgH2 is a promising and popular hydrogen storage material. In this work, the hydrogen desorption reactions of a single Pd atom adsorbed MgH2(110) surface are investigated by using first-principles density functional theory calculations. We find that a single Pd atom adsorbed on the MgH2(110) surface can significantly lower the energy barrier of the hydrogen desorption reactions from 1.802 eV for pure MgH2(110) surface to 1.154 eV for Pd adsorbed MgH2(110) surface, indicating a strong Pd single-atom catalytic effect on the hydrogen desorption reactions. Furthermore, the Pd single-atom catalysis significantly reduces the hydrogen desorption temperature from 573 K to 367 K, which makes the hydrogen desorption reactions occur more easily and quickly on the MgH2(110) surface. We also discuss the microscopic process of the hydrogen desorption reactions through the reverse process of hydrogen spillover mechanism on the MgH2(110) surface. This study shows that Pd/MgH2 thin films can be used as good hydrogen storage materials in future experiments.

Investigation of structural, electronic and lattice dynamical properties of XNiH3 (X = Li, Na and K) perovskite type hydrides and their hydrogen storage applications

XNiH3 (X = Li, Na, and K) perovskite type hydrides have been studied by using Density Functional Theory (DFT) and these materials are found to be stable and synthesizable. The X-ray diffraction patterns have been obtained and they indicate that all materials have the polycrystalline structure. The electronic properties have been investigated and it has been found that these structures show metallic character. The Bader partial charge analysis has also been performed. In addition, the elastic constants have been calculated and these materials are found to be mechanically stable. Using these elastic constants, the mechanical properties such as bulk modulus, shear modulus, Poisson's ratio have been obtained. Moreover, the Debye temperatures and thermal conductivities have been studied. The anisotropic elastic properties have been visualized in three dimensions (3D) for Young's modulus, linear compressibility, shear modulus and Poisson's ratio as well as with the calculation of the anisotropic factors. Additionally, the dynamical stability has been investigated and obtained phonon dispersion curves show that these materials are dynamically stable. Also, the thermal properties including free energy, enthalpy, entropy and heat capacity have been studied. The hydrogen storage properties have been examined and the gravimetric hydrogen storage capacities have been calculated as 4.40 wt%, 3.57 wt% and 3.30 wt% for LiNiH3, NaNiH3 and KNiH3, respectively. Furthermore, the hydrogen desorption temperatures have been obtained as 446.3 K, 419.5 K and 367.5 K for LiNiH3, NaNiH3 and KNiH3, respectively.

MgTiO3Hx and CaTiO3Hx perovskite compounds for hydrogen storage applications

The first principle calculations are used to investigate hydrogen storage properties of MgTiO3Hx and CaTiO3Hx (x = 0, 3, 6, and 8) perovskite compounds in cubic phase (Pm3 m). In order to examine the stability of these compounds, formation enthalpies are calculated and all compounds (except MgTiO3H6 and MgTiO3H8) are found to be stable. The second order elastic constants and related polycrystalline elastic moduli (e.g., shear modulus, Young's modulus, Poisson's ratio, Debye temperature, sound velocities) are determined and the results are discussed in detail. The mechanical stability determination indicates that MgTiO3, CaTiO3, and CaTiO3H6 compounds are only stable compounds and also MgTiO3 and CaTiO3H6 are ductile while CaTiO3 is a brittle material. Also, the mechanical anisotropy is discussed via two-dimensional (2D) and three-dimensional (3D) surfaces for mechanical stable compounds and they are found to have anisotropic behaviour (except linear compressibility for MgTiO3, CaTiO3). Electronic band structure and corresponding partial density of states (PDOS) and charge density have been plotted. Bader charge analysis have been done. MgTiO3 has metallic behaviour whereas CaTiO3 and CaTiO3H6 have semiconductor behaviour. Among all compounds, CaTiO3H6 is found to be only one that could be used in the hydrogen storage applications. For this compound, the gravimetric hydrogen storage capacity is calculated as 4.27 wt% and the hydrogen desorption temperature is obtained as 827.1 K.

Effect of LiCe(BH4)3Cl with a high Li ion conductivity on the hydrogen storage properties of Li[sbnd]Mg[sbnd]N[sbnd]H system

The effect of LiCe(BH4)3Cl on the hydrogen storage properties of Mg(NH2)22LiH system was studied systematically, which has a high Li ion conductivity. The hydrogen desorption temperatures for LiMgNH system shift to lower temperatures by 0.05LiCe(BH4)3Cl doping with the onset temperature of dehydrogenation decreasing by 40 °C and the peak temperature decreasing by 30 °C. The Mg(NH2)22LiH–0.03LiCe(BH4)3Cl composite exhibits an improved comprehensive hydrogen storage properties, which can reversibly store about 5.0 wt% hydrogen at 160 °C, and released hydrogen as much as 8.6 times faster than that of the Mg(NH2)22LiH composite at 160 °C. The results indicated that the LiCe(BH4)3Cl-containing sample exhibited much better cycling properties than that of Mg(NH2)22LiH sample. XRD and FTIR results show that the structure of LiCe(BH4)3Cl does not change before and after hydrogen absorption/desorption, indicating it plays the catalytic effect. The hydrogen desorption activation energy of Mg(NH2)22LiH doped with 0.03LiCe(BH4)3Cl was reduced by 37.5%. The rate-controlling step of desorption shifted from the diffusion to the chemical reaction by the addition of LiCe(BH4)3Cl, indicating that the diffusion rates of small ions like H+, Li+ and Mg2+ in LiMgNH system are significantly enhanced, which could be well explained by the improved ionic conductivity of LiCe(BH4)3Cl doped sample.

Low temperature de/hydrogenation in the partially crystallized Mg60Ce10Ni20Cu10 metallic glasses induced by milling with process control agents

Slow hydrogen de/absorption kinetics and high hydrogen desorption temperature are still great challenges for both crystalline and amorphous Mg-based alloys. In this work, through using ethanol (E) and ethylene glycol (EG) as milling process control agents (PCAs), partial and controllable crystallization of the melt-spun Mg60Ce10Ni20Cu10 metallic glass was achieved. The microstructure of the as-milled powders and corresponding hydrides was characterized by DSC, SEM, TEM and XRD. De/hydrogenation properties were measured by automatic Sieverts-type apparatus and TG-MS. It was found that the PCAs could lead to partial crystallization of the Mg60Ce10Ni20Cu10 metallic glass due to the dissolving of oxygen into the amorphous structure from PCAs. The introduction of a small amount of the nanocrystals promoted greatly hydrogen de/absorption properties of the melt-spun Mg60Ce10Ni20Cu10 alloy. The hydrogenation temperature could be decreased to below 100 °C and the initial hydrogen desorption temperature of the EG-added hydride could be decreased to below 150 °C. The structure evolution of the de/hydrogenated samples of the EG-added powder was also studied. The hydrogen-induced crystallization was evidently observed in the hydrogenated sample. The ethanol and ethylene glycol was found to be effective milling PCAs to create a composite structure of amorphous and crystalline, and the composite structure greatly enhanced the de/hydrogenation properties. However, the structural stability and reversibility of such composite structure during hydrogenation were still great challenges.

Improved hydrogen storage performances of Mg-Y-Ni-Cu alloys by melt spinning

In the article, melt spinning was successfully applied to prepare Mg25-xYxNi9Cu (x = 0, 1, 3, 5, 7) alloys. The alloys were detected by the equipment of TEM and XRD to describe the structure of the alloys. Sievert’s apparatus, DSC and TGA connected with a H2 detector were utilized to investigate properties of absorbing and desorbing hydrogen. We utilized Arrhenius and Kissinger methods to reckon activation energy for desorbing hydrogen from the alloy hydrides. It is found that melt spinning and Y substitution for Mg visibly decrease the thermodynamic parameters (ΔH and ΔS) as well as make starting hydrogen desorption temperature obviously decline. For this kind of alloy, Y taking place of Mg distinctly decreases the hydrogen absorption capacity. The hydrogen absorption capacity augments at first and afterward declines following spinning rate increasing. Y replacing Mg and melt spinning slightly impair the kinetics for absorbing hydrogen, but make the kinetics for desorbing hydrogen significantly improved. The activation energy of desorbing hydrogen from the alloys markedly lowers following the proportion of Y and spinning rate increasing, which is identified as the root-cause that affect the velocity of hydrogen desorption reaction.

Synergistic catalysis in monodispersed transition metal oxide nanoparticles anchored on amorphous carbon for excellent low-temperature dehydrogenation of magnesium hydride

Magnesium hydride (MgH2) has been considered to be one of the most promising solid-state hydrogen storage materials owing to its high hydrogen capacities, excellent reversibility and abundant source. However, the high dehydrogenation energy barrier and poor kinetics embarrass the practical application of MgH2 in fuel cell. Doping nano-catalyst is deemed to be the most effective method to improve kinetics property of hydrogen storage materials, but the nanoparticles generally suffer from agglomeration and inactivation during the cycling hydrogen storage. Here we present a promising strategy to facilely prepare a high-efficiency transition metal oxide nano-catalyst, TiO2 nanoparticles, in which monodispersed single-crystal-like TiO2 nanoparticles are wrapped with amorphous carbon. The in-situ synthesized TiO2 nanoparticles/amorphous carbon catalyst exhibit superior catalytic effect on the dehydrogenation properties of MgH2. A significant reductions of hydrogen desorption temperature (163.5 °C) and activation energy (69.2 kJ mol−1) have been obtained for the TiO2 nanoparticles/amorphous carbon catalyzed MgH2, which can be fully rehydrogenated with a reversible capacity of about 6.5 wt% at 200 °C within 5 min, and then completely dehydrogenated at 275 °C within 10 min. It is demonstrated that such significantly improved hydrogen desorption properties can be attributed to the in-situ formation of TiO2 nanoparticles, amorphous carbon and multi-valance Ti species, which play the synergistically catalytic roles in the nano-catalyst. In particular, the presence of amorphous carbon in the catalyst can not only prevent the aggregation and growth of catalyst nanoparticles, but also dramatically reduce the desorption energy value of H in MgH2, according to the density functional theory calculation. This finding opens a new venue for the synthesis of monodispersed single-crystal-like TiO2 nanoparticles/amorphous carbon catalyst with high-activity, safety, low cost, and its practical application in MgH2 and other hydrogen storage systems.

Gaseous hydrogen storage properties of Mg-Y-Ni-Cu alloys prepared by melt spinning

For purpose of promoting the hydrogen absorption and desorption thermodynamics and kinetics properties of MgNi-based alloys, partially substituting Y and Cu for Mg and Ni respectively and melt spinning technique were applied for getting Mg25–xYxNi9Cu (x = 0–7) alloys. Their microstructures and phases were characterized with the help of X-ray diffraction and transmission electron microscopy. Their hydrogen absorbing and desorbing properties were tested by a Sievert apparatus, DSC, and TGA, which were connected with a H2 detector. In order to estimate the dehydrogenation activation energy of alloy hydride, both Arrhenius and Kissinger methods were applied for calculation. It is found that their hydriding kinetics notably declines, however, their hydrogen desorption kinetics conspicuously improves, with spinning rate and Y content increasing. Their hydrogen desorption activation energy markedly decreases under the same constraint, and it is found that melt spinning and Y substituting Mg improve the real driving force for dehydrogenation. As for the tendency of hydrogen absorption capacity, it presents an elevation firstly and soon after a decline with the rising of spinning rate, however, it always lowers with Y content growing. With Y content and spinning rate increasing, their thermodynamic parameters (ΔH and ΔS absolute values) visibly decrease, and the starting hydrogen desorption temperatures of alloy hydrides obviously lower.

Dependence of trapping states on the hydrogen content of high-carbon ferrite-austenite dual-phase steel

States of hydrogen present in high carbon ferrite (α)-austenite (γ) dual phase steel were analyzed under various hydrogen charging conditions using thermal desorption analysis (TDA). Specimens including 0%γ and 10%γ in α were prepared. The 10%γ specimen consisted of bainitic ferrite and thermally stable retained austenite. When the 10%γ specimen were charged with hydrogen under high fugacity condition, the amount of hydrogen rapidly increased, the end temperature of hydrogen desorption in TDA profile increased, the hydrogen degassing time at 30 ° C increased, and the trap activation energy increased from about 30 kJ/mol to 47 kJ/mol. This 47 kJ/mol value is in excellent agree with the activation energy of hydrogen diffusion in γ phase. These results probably indicated that hydrogen is not absorbed in γ phase but α phase under lower fugacity conditions, i.e., lower amount of hydrogen. In contrast, hydrogen is absorbed in not only α phase but also γ phase under higher fugacity conditions, i.e., higher amount of hydrogen.

Improved hydrogen storage performance of as-milled Sm–Mg–Ni alloy by adding CeO2

To investigate the influence of adding CeO2 on the hydrogen storage characteristics of Sm–Mg–Ni-based SmMg11Ni-type alloy, mechanical milling was utilized to synthesize SmMg11Ni and SmMg11Ni + 5 wt.% CeO2 (named SmMg11Ni–5CeO2) alloys. The microstructure of as-cast and as-milled samples was measured via X-ray diffractometer and transmission electron microscope. Sieverts device was utilized to measure the isothermal hydriding and dehydriding kinetics. The non-isothermal dehydrogenation performance was explored by thermogravimetry and differential scanning calorimetry. The hydrogen desorption activation energy of the compound metal hydride can be computed by both Arrhenius and Kissinger methods. The related data show that adding CeO2 can engender a very slight influence on the hydrogen storage thermodynamics, but it can result in an obvious reduction in hydrogen absorption and desorption capacities. Furthermore, the hydrogen desorption performance of experimental alloys is conspicuously ameliorated by the addition of CeO2, viz. lowering the initial hydrogen desorption temperature and enhancing hydrogen desorption rate. The hydrogen desorption activation energies with and without CeO2 addition are 84.28 and 100.31 kJ/mol, respectively, with an obvious decrease of 16.03 kJ/mol. This is thought to be responsible for the ameliorated hydrogen desorption kinetics by adding CeO2.

Improvement of Hydrogen Desorption Characteristics of MgH₂ With Core-shell Ni@C Composites.

Magnesium hydride (MgH2) has become popular to study in hydrogen storage materials research due to its high theoretical capacity and low cost. However, the high hydrogen desorption temperature and enthalpy as well as the depressed kinetics, have severely blocked its actual utilizations. Hence, our work introduced Ni@C materials with a core-shell structure to synthesize MgH2-x wt.% Ni@C composites for improving the hydrogen desorption characteristics. The influences of the Ni@C addition on the hydrogen desorption performances and micro-structure of MgH2 have been well investigated. The addition of Ni@C can effectively improve the dehydrogenation kinetics. It is interesting found that: i) the hydrogen desorption kinetics of MgH2 were enhanced with the increased Ni@C additive amount; and ii) the dehydrogenation amount decreased with a rather larger Ni@C additive amount. The additive amount of 4 wt.% Ni@C has been chosen in this study for a balance of kinetics and amount. The MgH2-4 wt.% Ni@C composites release 5.9 wt.% of hydrogen in 5 min and 6.6 wt.% of hydrogen in 20 min. It reflects that the enhanced hydrogen desorption is much faster than the pure MgH2 materials (0.3 wt.% hydrogen in 20 min). More significantly, the activation energy (EA) of the MgH2-4 wt.% Ni@C composites is 112 kJ mol−1, implying excellent dehydrogenation kinetics.

Electrochemical deposited Mg-PPy multilayered film to store hydrogen

The stability of magnesium and its hydride (Mg/MgH2) against moisture and oxygen can be improved by forming a multilayered structure with a protective polymeric layer. Herein, we report for the first time the fabrication of such a multilayered structure via an electrochemical deposition method consisting of the successive depositions of Mg on electropolymerised polypyrrole (PPy) films. The thickness of the PPy and the Mg layers was ∼1 μm, which is larger than the Mg/Pd multilayers prepared via physical deposition methods, owing to the higher surface roughness of electropolymerised films. However, such films displayed remarkable hydrogen storage properties. Hydrogenation of the PPy/Mg film was achieved at 100 °C and hydrogen release started from 125 °C with a peak at ∼215 °C. When covered by a second PPy layer, the hydrogen desorption temperature increased slightly to 230 °C. These hydrogen absorption and desorption temperatures are significantly lower than that of pristine Mg/MgH2 micron sized powders and this was achieved without any additional catalyst. Furthermore, such hydrogenated PPy/Mg/PPy film structures were found to be stable in air even after one week.

Hydrogen storage performances of as-milled REMg11Ni (RE=Y, Sm) alloys catalyzed by MoS2

Abstract To compare the hydrogen storage performances of as-milled REMg11Ni-5MoS2 (mass fraction) (RE=Y, Sm) alloys, which were catalyzed by MoS2, the corresponding alloys were prepared. The hydrogen storage performaces of these alloys were measured by various methods, such as XRD, TEM, automatic Sievert apparatus, TG and DSC. The results reveal that both of the as-milled alloys exhibit a nanocrystalline and amorphous structure. The RE=Y alloy shows a larger hydrogen absorption capacity, faster hydriding rate, lower initial hydrogen desorption temperature, superior hydrogen desorption property, and lower hydrogen desorption activation energy, which is thought to be the reason of its better hydrogen storage kinetics, as compared with RE=Sm alloy.

Synthesis of β-Ti-Nb alloys from elemental powders by high-energy ball milling and their hydrogenation features

The body-centered cubic (BCC or β) titanium alloys are attractive materials for hydrogen storage applications, due to their relatively high absorption capacities that can be attained in some cases, even at room or moderate temperatures. It is known that the ball milling techniques improve the H-absorption/desorption kinetics. Thus, different compositions with Ti/Nb atomic ratios of 1.0, 1.5 and 2.3 were prepared by mechanical alloying (MA) and reactive milling (RM), and the composition effects on the microstructure and the hydrogenation properties were characterized. Both procedures, MA and RM, were able to produce TixNb1-x BCC alloys. It was observed a significant influence of Ti/Nb atomic ratios on lattice parameters, crystallite and particle sizes, effective kinetic parameter, Avrami exponent, hydrogen storage capacities, reversibility, and desorption temperature ranges. The RM synthesized hydrides acquired better H-absorption/desorption properties than the TiNb hydrides produced by mechanical alloying hydrogenated at 250–300 °C. The results demonstrated changes in the hydride nucleation manner and improvement of the hydrogenation rates when the Nb addition is increased.

Study of borohydride ionic liquids as hydrogen storage materials

Abstract Stability of borohydrides is determined by the localization of the negative charge on the boron atom. Ionic liquids (ILs) allow to modify the stability of the borohydrides and promote new dehydrogenation pathways with a lower activation energy. The combination of borohydride and IL is very easy to realize and no expensive rare earth metals are required. The composite of the ILs with complex hydrides decreases the enthalpy and activation energy for the hydrogen desorption. The Coulomb interaction between borohydride and IL leads to a destabilization of the materials with a significantly lower enthalpy for hydrogen desorption. Here, we report a simple ion exchange reaction using various ILs, such as vinylbenzyltrimethylammonium chloride ([VBTMA][Cl]), 1-butyl-3-methylimidazolium chloride ([bmim][Cl]), and 1-ethyl-1-methylpyrrolidinium bromide ([EMPY][Br]) with NaBH4 to decrease the hydrogen desorption temperature. Dehydrogenation of 1-butyl-3-methylimidazolium borohydride ([bmim][BH4]) starts below 100 °C. The quantity of desorbed hydrogen ranges between 2.4 wt% and 2.9 wt%, which is close to the theoretical content of hydrogen. The improvement in dehydrogenation is due to the strong amine cation that destabilizes borohydride by charge transfer.

The use of nano-silicon carbide and nickel as catalyst in magnesium hydrides (MgH2) for hydrogen storage material application

Magnesium (Mg) is currently known as one of the potential candidates for hydrogen absorbent material because theoretically, it has the ability to absorb hydrogen in large quantities of 7.6 wt%. However, the kinetic reaction of Mg is very slow; to absorb hydrogen takes 60 min with high operating temperature (>400 °C). Therefore, we have studied MgH2-Ni-SiC-based storage system. The objective of this study is to improve the hydrogen desorption temperature and the hydrogen desorption capacity. The material preparation was done through mechanical alloying technique. In this method, the milling of the material was carried out within 5 h, 10 h and 15 h, with the ratio of the ball to powder, was 10:1 with the catalyst by 5 wt% and 10 wt% SiC. The results from XRD measurements revealed that the sample was successfully reduced to a nanocrystal scale. The phase emerging from the XRD observation is the phase MgH2 as the main phase and followed by Ni and SiC phase as the minor phase. Our SEM observation showed the irregular particle shape, the particle size in the sample is not homogeneous because of the agglomeration effect and coldwelding that causes the particle size to look larger. Based on the observation with DSC, the temperature obtained in the samples milled 10 h with catalyst 5 wt% SiC was 365 °C.