Hydrogen Desorption Capacity Research Articles

Effect of multi-wall carbon nanotubes supported nano-nickel and TiF3 addition on hydrogen storage properties of magnesium hydride

Multi-wall carbon nanotubes supported nano-nickel (Ni/MWCNTs) with superior catalytic effects was introduced to magnesium hydride by the process of hydriding combustion synthesis (HCS) and mechanical milling (MM). The effect of different Ni/MWCNTs contents (5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%) on the hydrogenation and dehydrogenation properties of the composite was investigated systematically. It is revealed that Mg85-(Ni/MWCNTs)15 composite shows the best comprehensive hydrogen storage properties, which absorbs 5.68 wt.% hydrogen within 100 s at 373 K and releases 4.31 wt.% hydrogen within 1800 s at 523 K under initial hydrogen pressures of 3.0 and 0.005 MPa, respectively. The in situ formed nano-Mg2Ni and MWCNTs have excellent catalytic effect on the hydrogenation and dehydrogenation performances of MgH2. To further improve the hydrogen absorption/desorption properties, TiF3 was added to the Mg–Ni/MWCNTs system. The result shows that TiF3 addition has little influence on the thermodynamic performance, but affects greatly the kinetic properties. The Mg85-(Ni/MWCNTs)15-TiF3 composite exhibits an appreciably enhanced hydrogen desorption performance at low temperature, and the hydrogen desorption capacity within 1800 s at 473 K for the TiF3-added composite is approximately four times the capacity of Mg85-(Ni/MWCNTs)15 under the same condition. The catalytic effects during hydrogenation and dehydrogenation have been discussed in the study.

Hydrogen adsorption and desorption with 3D silicon nanotube-network and film-network structures: Monte Carlo simulations

Hydrogen is clean, sustainable, and renewable, thus is viewed as promising energy carrier. However, its industrial utilization is greatly hampered by the lack of effective hydrogen storage and release method. Carbon nanotubes (CNTs) were viewed as one of the potential hydrogen containers, but it has been proved that pure CNTs cannot attain the desired target capacity of hydrogen storage. In this paper, we present a numerical study on the material-driven and structure-driven hydrogen adsorption of 3D silicon networks and propose a deformation-driven hydrogen desorption approach based on molecular simulations. Two types of 3D nanostructures, silicon nanotube-network (Si-NN) and silicon film-network (Si-FN), are first investigated in terms of hydrogen adsorption and desorption capacity with grand canonical Monte Carlo simulations. It is revealed that the hydrogen storage capacity is determined by the lithium doping ratio and geometrical parameters, and the maximum hydrogen uptake can be achieved by a 3D nanostructure with optimal configuration and doping ratio obtained through design optimization technique. For hydrogen desorption, a mechanical-deformation-driven-hydrogen-release approach is proposed. Compared with temperature/pressure change-induced hydrogen desorption method, the proposed approach is so effective that nearly complete hydrogen desorption can be achieved by Si-FN nanostructures under sufficient compression but without structural failure observed. The approach is also reversible since the mechanical deformation in Si-FN nanostructures can be elastically recovered, which suggests a good reusability. This study may shed light on the mechanism of hydrogen adsorption and desorption and thus provide useful guidance toward engineering design of microstructural hydrogen (or other gas) adsorption materials.

Improved hydrogen storage properties of combined Ca(BH4)2 and LiBH4 system motivated by addition of LaMg3 assisted with ball milling in H2

A combined Ca(BH4)2+LiBH4 system with improved hydrogen storage properties is obtained by the addition of a particulate LaMg3 alloy assisted with ball milling in a H2 atmosphere. It is found that LaMg3 is mostly hydrogenated to symbiotic low crystalline MgH2 and amorphous La-containing hydride of fine particles after the milling, which are homogenously embedded in the Ca(BH4)2+LiBH4 matrix. The multi-hydride system shows significant improvements in both hydrogen storage thermodynamics and kinetics. Particularly, the system with LaMg3 addition in a molar ratio of 0.3 shows an overall superior hydrogen storage property. The main dehydrogenation starts from ca. 200 °C, which is 100 °C lower than the main dehydrogenation temperature of the pristine Ca(BH4)2+LiBH4 system. Re-hydrogenation initiates at a low temperature of ca. 150 °C, and the system maintains 70% of its first hydrogen desorption capacity after 5 cycles. The mechanism of the improved hydrogen storage properties of the combined system is discussed.

Hydrogen storage properties of MgH2 + 20 wt.% Na2WO4 composite

The hydrogen storage properties of MgH2 ball milled with 20wt.% Na2WO4 have been investigated. The MgH2+20wt.% Na2WO4 composite has favorable hydrogenation and dehydrogenation properties as well as low decomposition temperature. When compared with the pristine MgH2, the total hydrogen absorption capacity of MgH2+20wt.% Na2WO4 composite increased from 0.98wt.% to 2.27wt.% in 20min at 423K, and the maximum hydrogen desorption capacity of MgH2+20wt.% Na2WO4 composite increased by 1.3wt.% at 573K. DTA and the Kissinger desorption kinetics analysis results indicated that the dehydrogenation activation energy of MgH2+20wt.% Na2WO4 composite is 83.10kJ/mol, 39kJ/mol lower than that of the pristine MgH2. The XRD pattern provided that the in-situ formed MgWO4, acting as the catalyst during ball milling, improved the hydrogen storage properties of MgH2.

Effect of Sc substitution on hydrogen storage properties of Ti–V–Cr–Mn alloys

The microstructure and hydrogen absorption/desorption properties of (40-x)Ti–40V–10Cr–10Mn-xSc (x = 0, 5, 10, 15) were investigated. The result shows that the Sc-free sample has a V-based solid solution phase with body-center cubic structure (BCC phase), while the Sc-contained samples consist of a BCC phase, a C14-type Laves phase, a Sc-based hydride phase with face-center cubic (FCC) structure (derived from hydrogen decrepitation process). The hydrogen absorption kinetic process can be described by chemical reaction mechanism when x = 0, 10, 15 and 3-D diffusion mechanism when x = 5. As the Sc content increases, the hydrogen absorption capacity at 298 K first decreases and then increases, getting the minimum when x = 5. However, the hydrogen desorption capacity and hysteresis at 298 K are gradually improved with Sc content increasing.

Influence of annealing treatment on the microstructure and hydrogen storage performance of Ti1.02Cr1.1Mn0.3Fe0.6 alloy for hybrid hydrogen storage application

The as-cast Ti1.02Cr1.1Mn0.3Fe0.6 alloy for hybrid hydrogen storage vessel application was annealed at different temperatures (873K, 973K, 1123K, 1173K) for 2h, and annealed at 1123K for different time (2, 5, 8h) respectively, and their microstructure and hydrogen storage properties were investigated systematically. The results show that the as-cast alloy has a single C14 Laves phase, and all annealed alloys consist of a C14 Laves main phase and a secondary phase. After annealing at different temperatures for 2h, the hydrogen absorption pressure at 298K decreases, however, the maximum hydrogen storage capacity and desorption pressures at 318K decrease slightly too. As the annealing time extends, the hydrogen absorption plateau pressure at 298K and hydrogen desorption plateau pressure at 318K increase, and the hydrogen desorption capacity increases first and then decreases, which reaches the highest desorption capacity of 1.721wt.% at the annealing time of 5h. Among the studied alloys, the alloy annealed at 1123K for 5h has the best overall properties for hybrid hydrogen storage application, its hydrogen absorption plateau at 298K is 29.09MPa, its hydrogen desorption plateau pressure at 318K is 45.12MPa, its hydrogen storage capacity is 1.721wt.% and its dissociation enthalpy (ΔHd) is 17.78kJ/mol H2.

Decaying behaviors of V40(TiCr)51Fe8Mn hydrogen storage alloys with different particle sizes

The decaying behaviors of V40(TiCr)51Fe8Mn hydrogen storage alloys with different particle sizes from −60 to −500meshes were investigated systematically in this work. XRD results indicated that particle sizes of the alloys affect little on the phase transformation from Body-centered Cubic (BCC) to Body-centered Tetragonal (BCT) before and after hydrogenation and dehydrogenation, respectively. The hydrogen desorption capacities of the alloys decrease with increasing the number of hydrogen absorption–desorption cycles, but their decaying rates can be obviously restrained as starting particle sizes change from −60 down to −400meshes. Data fitting showed that the variation of the hydrogen desorption capacity has a similar exponential rule to cycle numbers as that of the micro-strain in the alloys. Possible reasons of the capacity decay are discussed. However, a superfine alloy with −500meshes showed much larger decaying rate, which was possibly attributed to the poisoning of foreign gases. Generally speaking, the smaller the particle size, the less the micro-strain in the lattice. Namely, the alloy powders with finer sizes have less micro-stress and correspondingly better cycling stability (within −400 meshes in this work).

Advanced high-pressure metal hydride fabricated via Ti–Cr–Mn alloys for hybrid tank

Ti–Cr–Mn-based alloys with a C14-type Laves structure have been investigated for potential application in hybrid high-pressure metal hydride tanks for fuel cell vehicles. The effects of partial substitution of Ti by Zr, and of Cr by Mo and W, on the hydrogen storage properties of Ti–Cr–Mn-based alloys have been systematically investigated. Among these alloys, (Ti0.85Zr0.15)1.1Cr0.9Mo0.1Mn shows the best overall properties, with a hydrogen desorption pressure and capacity of 9.54 atm and 1.78 wt% at 0 °C. The kinetics and cycling stability are also discussed for on-board hybrid high-pressure metal hydride tank applications. According to calculations, the volumetric H2 density of the hybrid system can reach the Department of Energy (DOE) 2017 target, while its gravimetric density remains at a high value of 2.72 wt% when 28% of the inner volume in a hybrid hydrogen metal hydride tank is filled with this alloy.

Effects of graphite content and compaction pressure on hydrogen desorption properties of Mg(NH2)2–2LiH based tank

Cylindrical lab-scale tank based on compacts of Mg(NH2)2–2LiH–0.07KOH mixed with expanded natural graphite (ENG) was designed. And the influences of ENG content and compaction pressure on the hydrogen desorption properties of the tank, including bed temperature, hydrogen flow rate and desorption capacity were investigated under the constant flow rate mode. As the ENG content increases, the heat transfer property of the hydride bed improves significantly, which results in the rise of the central temperature of the hydride bed and the increase of the hydrogen desorption time at the constant flow rate. As the compaction pressure increases, the hydrogen permeability of the hydride bed decreases obviously, but the entire desorption process changes a little. The results indicate that the heat transfer behavior of the hydride bed dominates the hydrogen desorption process of the tank.

Effects of compaction pressure and graphite content on hydrogen storage properties of Mg(NH2)2–2LiH hydride

Preparation of hydride–graphite compacts serves as an effective method to improve the volumetric hydrogen storage density and the effective thermal conductivity for light complex hydrides. This paper presents the effects of compaction pressure and expanded natural graphite (ENG) content on the hydrogen storage properties of the Mg(NH2)2–2LiH–0.07KOH compacts. The results show that the hydrogen desorption kinetics of the 1st sorption cycle decreases with the increase of the compaction pressure. However, the compacts exhibit the similar hydrogen desorption kinetics and capacities from the 2nd sorption cycles on regardless of the compaction pressure. The ENG addition significantly enhances the desorption kinetics because of the improvement of the heat transfer performance of the hydride. Furthermore, the volumetric hydrogen storage density of the hydride reaches 47 g/L after the compaction at 365 MPa, but it reduces by increasing the ENG content.

Effect of CO on hydrogen storage performance of KF doped 2LiNH2 + MgH2 material

(2LiNH2+MgH2) material is one of the most promising hydrogen storage materials. In applications, CO impurity in hydrogen has an effect on the hydrogen storage performance of (2LiNH2+MgH2) material. In this work, the effect of CO on the hydrogen storage properties of KF doped (2LiNH2+MgH2) material was investigated by using hydrogen containing 1mol% CO as the hydrogenation gas source. The results indicate that the hydrogen desorption capacity of the hydride decreases from 4.73wt.% to 3.88wt.% after 5 hydrogenation cycles. The decrease of the capacity is attributed to the permanent loss of the NH2 caused by the formation of Li2CN2 and KCN. Moreover, the hydrogen desorption kinetics declines obviously, and the dehydrogenation activation energy increases from 122.1kJ/mol to 132.0kJ/mol. Furthermore, it is found that the hydrogen desorption kinetics cannot be recovered to the initial level after re-milling. The main reason for these is that the catalytic effect on (Mg(NH2)2+2LiH+0.05KF) system disappears due to the transformation from KH to KCN.

Effect of Mg content on structure, hydrogen storage properties and thermal stability of melt-spun Mgx(LaNi3)100−x alloys

Amorphous Mgx(LaNi3)100−x (x = 40, 50, 60, 70) alloys with ribbon shape (5 mm wide, 0.2 mm thick) have been prepared by rapid solidification, using a melt-spinning technique. Their microstructure, hydrogen storage properties and thermal stability were studied by means of XRD, SEM, PCTPro2000 and DSC analysis, respectively. The results indicated that when Mgx(LaNi3)100−x alloys have been hydrogenated at 573 K under 2 MPa hydrogen pressure, LaH3 phase is formed in the case of x (x = 40, 50, 60, 70), Mg2NiH4 phase formed in the case of x (x = 40, 50, 60, 70), Mg2NiH0.3 phase formed in the case of x (x = 40, 50), and MgH2 phase formed in the case of x = 70. Experimental data of hydrogen desorption kinetics, tested at 523 K, 573 K and 623 K, are in good agreement with Avrami–Erofeev equation. The maximum hydrogen absorption capacity is 2.71 wt.% for Mg70(LaNi3)30 and 2.35 wt.% for Mg70(LaNi3)30, the increase of hydrogen desorption capacity is in the order of x = 70 > x = 60 > x = 50 > x = 40. Based on DSC analysis, the activation energies for dehydrogenation of these samples are calculated to be 122 ± 2 kJ/mol (x = 40) > 101 ± 3 kJ/mol (x = 50) > 84 ± 5 kJ/mol (x = 60) > 64 ± 3 kJ/mol (x = 70), which are in agreement with the results of hydrogen desorption kinetics.

Effects of Co Substitution for Ni on Microstructures and Electrochemical Properties of LaNi3.8 Hydrogen Storage Alloys

The effects of Co partial substitution for Ni on the microstructures and the electrochemical properties of the LaNi3.8-type phase LaNi3.8-xCox (x=0.0, 0.2, 0.4, 0.6) alloys were systematically studied. All the alloys mainly consist of LaNi5-type phase, rhombohedral Ce5Co19-type phase and hexagonal Pr5Co19-type phase. With increasing Co content, the relative abundance of each phase changes while the cell volume increases monotonously, which lower the hydrogen desorption pressure down to the desirable range (0.01~0.1 MPa) for hydride electrode of Ni/MH battery. All the Co-containing alloys display an enhanced cycle ability compared to LaNi3.8 alloy. The LaNi3.4Co0.4 alloy has the biggest discharge capacity, which is consistence with the solid hydrogen desorption capacity of the alloy. The LaNi3.6Co0.2 alloy exhibits the best rate performance corresponding to its maximum exchange current density (Io) and minimum charge transfer resistance (Rct).

Effect of Co substitution for La on hydrogen storage properties and thermal stabilities of amorphous Mg60Ni30La10−xCox (x = 0, 2 and 4) alloys prepared by melt spinning

A comparison of the hydrogen storage properties and thermal properties of amorphous Mg60Ni30La10−xCox hydrogen storage alloys prepared by melt spinning has been investigated. A, B and C were used to represent each alloy composition when x = 0, 2 and 4 respectively. Their microstructures, the hydrogen storage properties and the thermal stabilities were analysed by X-ray diffraction (XRD), PCTPro2000 and differential scanning calorimetry (DSC) respectively. After hydrogenation of Mg60Ni30La10−xCox (A, B and C) samples at 573 K under 2 MPa hydrogen pressure, XRD pattern results indicate the formation of new phases of MgH2 (A, B, C), Mg2NiH4 (A, B, C), La4H12·19 (A, B, C), Mg2Ni0·9Co0·1H4 (B), Mg2NiH0·26 (C) and Mg2CoH2 (C). It is observed that the experimental data of hydrogen desorption kinetics at 523, 573 and 623 K are well fitted through Avrami–Erofeev equation, and the hydrogen desorption kinetics is in the order of C>B>A. In addition, with increasing Co content, alloy C has the maximum hydrogen absorption capacity of 3·05 wt-% and the maximum hydrogen desorption capacity of 2·85 wt-%. Based on the results of DSC analysis, dehydrogenation activation energies of these alloys are determined to be 98·31±2·82 kJ mol−1 (A), 96·33±5·61 kJ mol−1 (B) and 78·99±2·98 kJ mol−1 (C), which are in accordance with the results of hydrogen desorption kinetics.

Superior dehydrogenation performance of nanoscale lithium borohydride modified with fluorographite

A significant enhancement in the dehydrogenation performance of LiBH4 is achieved by modifying with fluorographite (FGi). In-depth investigations show that the dehydrogenation thermodynamics and kinetics of LiBH4 are strongly improved by ball milling LiBH4 with FGi. The ball-milled LiBH4–FGi (mass ratio of 1:1) composite starts to release hydrogen without impurity gas at around 180 °C, and obtains a hydrogen desorption capacity of 7.2 wt% below 200 °C in seconds, which is improved dramatically compared with pristine ball-milled LiBH4. Microscopic morphology indicates that numerous ∼90 nm spots formed on the surface of FGi. Based on the microstructure analyses combined with hydrogen storage performances, the prominent effect of FGi is largely attributed to the nano-modifying effect and the exothermic reaction between LiBH4 and FGi during the dehydrogenation process. Furthermore, partial reversibility of the LiBH4–FGi composite has been demonstrated and the mechanism underlying the cycling capacity loss is discussed. The use of FGi may shed light on future study on searching for new strategies to improve both the thermodynamics and kinetics of light-metal complex hydrides.

A comparative study for synthesis methods of nano-structured (9Ni–2Mg–Y) alloy catalysts and effect of the produced alloy on hydrogen desorption properties of MgH2

9Ni–2Mg–Y alloy powders were prepared by arc melting, induction melting, mechanical alloying, solid state reaction and subsequent ball milling processes. The results showed that melting processes are not suitable for preparation of 9Ni–2Mg–Y alloy due to high losses of Mg and Y. Therefore, 9Ni–2Mg–Y alloy powder was prepared by three methods including: 1) mechanical alloying, 2) mechanical alloying + solid state reaction + ball milling, and 3) mixing + solid state reaction + ball milling. The prepared 9Ni–2Mg–Y alloy powders were compared for their catalytic effects on hydrogen desorption of MgH2. It is found that 9Ni–2Mg–Y alloy powder prepared by mechanical alloying + solid state reaction + ball milling method has a smaller particle size (1–5 μm) and higher surface area (1.7 m2 g−1) than that of other methods. H2 desorption tests revealed that addition of 9Ni–2Mg–Y alloy prepared by mechanical alloying + solid state reaction + ball milling to MgH2 decreases the hydrogen desorption temperature of MgH2 from 425 to 210 °C and improves the hydrogen desorption capacity from 0 to 3.5 wt.% at 350 °C during 8 min.

Study on glass-forming ability and hydrogen storage properties of amorphous Mg60Ni30La10 − xCox (x = 0, 4) alloys

Mg60Ni30La10−xCox (x=0, 4) amorphous alloys were prepared by rapid solidification, using a melt-spinning technique. X-ray diffraction and differential scanning calorimetry analysis were employed to measure their microstructure, thermal stability and glass-forming ability, and hydrogen storage properties were studied by means of PCTPro2000. Based on differential scanning calorimetry results, their glass-forming ability and thermal stability were investigated by Kissinger method, Lasocka curves and atomic cluster model, respectively. The results indicate that glass-forming ability, thermal properties and hydrogen storage properties in the Mg-rich corner of Mg–Ni–La–Co system alloys were enhanced by Co substitution for La. It can be found that the smaller activation energy (ΔΕ) and frequency factor (υ0), the bigger value of B (glass transition point in Lasocka curves), and higher glass-forming ability of Mg–Ni–La–Co alloys would be followed. In addition, atomic structure parameter (λ), deduced from atomic cluster model is valuable in the design of Mg–Ni–La–Co system alloys with good glass-forming ability. With an increase of Co content from 0 to 4, the hydrogen desorption capacity within 4000s rises from 2.25 to 2.85wt.% at 573K.

Ni–B-doped NaAlH4 hydrogen storage materials prepared by a facile two-step synthesis method

By directly introducing Ni–B into NaAlH4 system using a facile two-step synthesis method, the effects of Ni–B on NaAlH4 were systematically investigated. NaAlH4 can be completely formed after 30 h milling under 1 MPa hydrogen pressure. In addition, the dehydrogenation kinetics of as-prepared NaAlH4 after different milling times were investigated. As the dehydrogenation temperature rises, both the hydrogen desorption capacity and dehydrogenation rate quickly increase. The apparent activation energy E a for Ni–B-doped NaAlH4 is calculated to be 61.91 kJ·mol−1 for the first dehydrogenation step. More importantly, the dehydrogenation temperature of as-prepared NaAlH4 nanocrystalline can be reduced to about 100 °C.

Determination of kinetic parameters and hydrogen desorption characteristics of MgH2-10 wt% (9Ni–2Mg–Y) nano-composite

Hydrogen desorption kinetic parameters of MgH2 compounds were measured and compared with published gas solid reaction models. The compounds investigated in this study were as-received MgH2, ball milled MgH2, and MgH2 ball milled with 9Ni–2Mg–Y catalyst compound. It was determined that different models were necessary to fit the hydrogen desorption data collected at different temperatures on the same sample, indicating that desorption mechanisms changed with respect to temperature. Addition of (9Ni–2Mg–Y) alloy as a catalyst to MgH2 increased the hydrogen desorption capacity of MgH2 from zero (for as-received MgH2) to about 5 wt% at 350 °C within 500 s. The activation energy value was determined as 187 kJ/mol H2 for the as-received MgH2, 137 kJ/mol H2 for 20 h ball milled MgH2, and 62 kJ/mol H2 for 20 h ball milled MgH2-10 wt% (9Ni–2Mg–Y) nano-composite by the Arrhenius and Kissinger methods. Moreover, the integral heat of H2 desorption for the MgH2-10 wt% (9Ni–2Mg–Y) nano-composite was measured to be about 78 ± 0.5 kJ/mol H2 by adsorption micro-calorimetry consistent with the results of the Arrhenius and Kissinger methods.

Influence of structure of activated carbon with superhigh specific surface area on hydrogen storage capacity

Abstract