Hydrogen Desorption Properties Of MgH2 Research Articles

The anionic Tx defects of Nb2CTx MXene as the effective catalytically active center for the Mg-based hydrogen storage materials

While early transition metal-based materials, such as MXene, has emerged as an efficient catalyst for the Mg-based hydrogen storage materials, their strong interaction with hydrogen resulted in the high hydrogen diffusion barrier, hindering further improvement of catalytic activity. A MXene is characterized by rich anionic groups on its surface, significantly affecting electronic and catalytic functionalities. Using Nb2CTx as an example, we herein illustrate the critical role of anionic Tx defects on controlling hydrogen dissociation and diffusion processes in Mg-based hydrogen storage materials. The hydrogen desorption properties of MgH2 can be significantly enhanced by utilizing Tx controllable Nb2CTx, and it can release 3.57 wt.% hydrogen within 10 min under 240 °C with the reduced dehydrogenation activation barrier. It also realized stable de/hydrogenation reactions for at least 50 cycles. DFT studies combined with kinetic analysis revealed that the catalyst‒hydrogen interaction could be systematically controlled by optimizing surface Tx defect density, accelerating the hydrogen dissociation and diffusion processes at the same time. These results demonstrate that the Tx defects serve as the effective catalytically active centers of Nb2CTx, offering a flexible catalyst design guideline.

Enhanced hydrogen desorption properties of MgH2 by highly dispersed Ni: The role of in-situ hydrogenolysis of nickelocene in ball milling process

Magnesium hydride is a promising hydrogen storage material and how to improve its sorption kinetics is one of challenges in practical applications. In this paper, a new approach is proposed to catalyze MgH2 with highly dispersed Ni nanoparticles by in-situ hydrogenolysis of nickelocene (NiCp2) in ball milling process. After ball milling under 4 MPa hydrogen atmosphere for 15 h, the MgH2–16.1 wt% NiCp2 sample exhibits a homogeneous morphology where the in-situ formed Ni nanoparticles with size of ~8 nm are highly dispersed in MgH2 matrix. During initial dehydrogenation, Ni would react with MgH2 to form Mg2Ni which inherits the configuration of its high dispersion. In the subsequent hydrogen absorption and desorption cycles, the much fine and highly dispersed Ni-based catalytic phase contributes to the superior hydrogen desorption kinetics of MgH2 with a high-capacity retention rate of ~96% after 50 cycles. This work demonstrates that the in-situ formation of highly dispersed catalytic species is beneficial for improving hydrogen storage properties of MgH2.

Hydrogen Desorption Properties of MgH2 + 10 wt% SiO2 + 5 wt% Ni Prepared by Planetary Ball Milling

MgH2 is a very hopeful material for application as hydrogen storage material in the solid form. This is due to its reversibility and its ability to store large amounts of hydrogen, which is 7.6 wt%. However, this material still has weaknesses, namely high operating temperature and slow kinetic reactions. Various attempts have been made to overcome this weakness, including downsizing and adding catalyst. In this study, double catalyst was used, namely natural silica extracted from rice husk ash and nickel nano powder, with a composition of MgH2 + 10 wt% SiO2 + 5 wt% Ni. The purpose of this research was to study the effect of downsizing and using these catalysts to the thermodynamic and kinetic properties of the hydrogen storage material MgH2. Samples were prepared by using High Energy Ball Milling (HEBM), with variations in milling time of 1, 5, 10, and 15 hours. The X-ray Diffraction (XRD) pattern showed the presence of an impurity phase in the samples milled for 10 and 15 hours. It also showed a reduction in grain size with increasing milling time. However, agglomeration has occurred in the samples milled for 15 hours. From the Scanning Electron Microscope (SEM) results can be seen that the sample with longer milling time, were homogeneously distribute. Thermal investigation showed that the lowest desorption temperature was achieved in samples with milling time of 5 and 10 hours, namely 287 °C and 288 °C. This study shows that natural silica catalyst plays a role in improving the thermodynamic characteristics of MgH2, while Ni plays a role in improving the kinetic characteristics of MgH2. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Effects of single– and co– substitution of Ti and Fe on vacancy formation and dehydrogenation from MgH2 (110) surface: Ab initio study

In this paper, we studied the effect of single- and co-substitution of Ti and Fe on vacancy formation and hydrogen desorption on MgH2 (110) surface through first principles calculations. In the surface, we calculated and compared total electronic energies for all possible co-substitution systems in order to determine the preferential Ti and Fe co-substitution site. Substitution energy showed that Ti and Fe co-substitution is more energetically favourable than single-substitution of Ti or Fe in the surface. The bond length, DOS and Bader atomic charge were estimated in order to understand bonding mechanism between atoms. We also calculated formation energy for H, Mg and complex Mg-H vacancies and hydrogen desorption energies. More importantly, it was found that improvement in vacancy formation and hydrogen desorption becomes more obvious in Ti and Fe co-substitution system than single-substitution system. Our results indicated that Ti and Fe co-substitution in MgH2 (110) surface could be more effective method to improve poor hydrogen desorption properties of MgH2 than Ti or Fe single-substitution.

Improved hydrogen desorption properties of magnesium hydride with TiFe0.8Mn0.2, graphite and iron addition

The high dehydrogenation temperature of magnesium-based hydride (MgH2) is still a challenge as a potential hydrogen storage material in automobile applications. To improve the hydrogen desorption properties of MgH2; we selected TiFe0.8Mn0.2, graphite and Fe as additives. We prepared the Mg–graphite, Mg–TiFe0.8Mn0.2–Fe, Mg–TiFe0.8Mn0.2–graphite, Mg–Fe–graphite and Mg–TiFe0.8Mn0.2–Fe–graphite composites with high-energy ball milling under argon atmosphere. We investigated the effects of graphite and Fe addition to the desorption mechanism of TiFe0.8Mn0.2 using X-ray diffractometer (XRD), scanning electron microscope, differential scanning calorimeter and pressure-composition-temperature measurements using Sievert apparatus. We observed MgH2 in Mg–TiFe0.8Mn0.2–graphite, Mg–Fe–graphite and Mg–TiFe0.8Mn0.2–Fe–graphite with XRD analyses after hydrogenation at 200 °C under a hydrogen pressure of 2.5–2.6 MPa. As compared to pure milled MgH2 powder, we found that the dehydrogenation peak temperatures are decreased by 90, 160 and 165 °Cfor Mg–TiFe0.8Mn0.2–graphite, Mg–Fe–graphite, and Mg–TiFe0.8Mn0.2–Fe–graphite composites, respectively. The co-addition of TiFe0.8Mn0.2, graphite, and Fe exhibit the synergistic effects in improving the hydrogen desorption properties of MgH2.

In-situ Formed Al from the Hydrogenation of Al12Mg17 on Hydrogen Desorption Properties of MgH2

The influence of in-situ formed Al from hydrogenation of Al12Mg17 on hydrogen desorption properties of MgH2 was studied in this paper. Pure Al powders were also added to MgH2 by mechanical milling method and corresponding desorption properties was studied for comparison. Both of the samples showed enhanced hydrogen desorption properties than pure MgH2 while in-situ formed Al exhibited better catalyst effects than metallic Al powders.

Improved hydrogen desorption properties of MgH2 by graphite and NiF2 addition: experimental and first-principles investigations

The high dehydrogenation temperature is still the impediment for the practical application of magnesium-based hydride (MgH2) as a potential hydrogen storage medium. In order to improve the hydrogen desorption properties of MgH2, the graphite and NiF2 are selected as additives, and the MgH2–graphite and MgH2–graphite–NiF2 composites are prepared by high-energy ball milling. Using experimental X-ray diffraction, scanning electron microscopy, differential scanning calorimetry characterizations and first-principle calculations, the effects and mechanisms of graphite and NiF2 addition on the hydrogen desorption properties of MgH2 are systematically investigated. Experimental results show that the single addition of graphite is beneficial to the refinement of MgH2 grains and particles. The size of MgH2 particles can be further decreased after the co-addition of graphite and NiF2. Either the single addition of graphite or the co-addition of graphite and NiF2 reduces the dehydrogenation temperature of MgH2. As compared with pure milled MgH2, the dehydrogenation peak temperatures are decreased by 31 and 63 °C for MgH2–graphite and MgH2–graphite–NiF2 composites, respectively. Apparently, the co-addition of graphite and NiF2 exhibits the synergistic catalytic effects in improving the hydrogen desorption properties of MgH2. The first-principle calculations reveal that the co-addition of graphite and NiF2 leads to the structural distortion of MgH2 and results in the charge transfer between the additives and MgH2, which induce the weakened structural stability and decreased dehydrogenation enthalpy of MgH2. These may be the underlying reasons for the reduced dehydrogenation temperature of MgH2 with graphite and NiF2 addition.

Enhanced hydrogen desorption properties of magnesium hydride by coupling non-metal doping and nano-confinement

Magnesium hydride (MgH2) offers excellent capacity to store hydrogen, but it suffers from the high desorption temperature (>283 °C for starting release hydrogen). In this work, we calculated the hydrogen desorption energy of Mg76H152 clusters with/without non-metal dopants by density functional theory method. Phosphorus (P), as identified as the best dopant, can reduce the reaction energy for releasing one hydrogen molecule from 0.75 eV (bulk MgH2) to 0.20 eV. Inspired by the calculation, P-doped ordered mesoporous carbon (CMK-3) was synthesized by one-step method and employed as the scaffold for loading MgH2 nanoparticles, forming MgH2@P/CMK-3. Element analysis shows that phosphorus dopants have been incorporated into the CMK-3 scaffold and magnesium and phosphorus elements are well-distributed in carbon scaffold hosts. Tests of hydrogen desorption confirmed that P-doping can remarkably enhance the hydrogen release properties of nanoconfined MgH2 at low temperature, specifically ∼1.5 wt. % H2 released from MgH2@P/CMK-3 below 200 °C. This work, based on the combination of computational calculations and experimental studies, demonstrated that the combined approach of non-metal doping and nano-confinement is promising for enhancing the hydrogen desorption properties of MgH2, which provides a strategy to address the challenge of hydrogen desorption from MgH2 at mild operational conditions.

Synergistically thermodynamic and kinetic tailoring of the hydrogen desorption properties of MgH2 by co-addition of AlH3 and CeF3

The hydrogen desorption properties of MgH2 are thermodynamically and kinetically improved by the synergistic addition of AlH3 and CeF3.

Effect of Synthesized MgNi4Y Catalyst on Hydrogen Desorption Properties of Milled MgH2

It has been reported that ball milling and adding catalyst can improve hydrogen desorption properties of MgH2. In this study, simultaneous effect of adding catalyst and ball milling on hydrogen desorption properties of MgH2 was studied. Mechanical alloying and heat treatment methods were used to synthesize MgNi4Y intermetallic as a catalyst. In this regard, pure Mg, Ni, and Y elemental powders were ball milled in different conditions and then heat treated at 1073 K (800 °C) for 4 hours. XRD and FESEM methods were used to investigate properties of the samples. It was found that, after 10 hours of ball milling and then heat treating at 1073 K (800 °C), MgNi4Y intermetallic was formed almost completely. The results of Sievert tests showed that as-received MgH2 did not release any significant amount of hydrogen at 623 K (350 °C). But, after ball milling for 10 hours, 0.8 wt pct hydrogen was released from MgH2 at 623 K (350 °C) in 40 minutes. Adding 10 wt pct catalyst via ball milling to MgH2 led to releasing 3.5 wt pct hydrogen in the same conditions. In addition, increasing ball milling time from 10 to 65 hours increased the amount of released hydrogen from 51 to 85 pct of theoretical hydrogen desorption value and improved kinetic of desorption process.

Effect of microwave irradiation on the hydrogen desorption properties of MgH2/LiBH4 composite

The effect of microwave irradiation on the hydrogen desorption properties of MgH2+xLiBH4 (x=0–30wt%) composite was systematically investigated. The results show that the composite can be heated rapidly with the addition of LiBH4 by microwave heating which brings about the fast dehydrogenation of MgH2. The heating rate of the samples depends on the content of LiBH4 and the microwave power, because LiBH4 acts as a microwave absorber above 107°C. Isothermal kinetic results showed that the amount of hydrogen released from MgH2+10wt% LiBH4 under microwave is 5 times more than that of under conventional heating at 300°C in 30min. After five cycles of hydrogen sorption at 350°C, the sample can be heated even more rapidly by microwave heating. These results demonstrate that the microwave heating is an effective technology to improve the hydrogen desorption kinetics of the MgH2/LiBH4 composite with high energy efficiency. Causes for the improved microwave heating were discussed and a potential mechanism was proposed.

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.

Hydrogen desorption properties of MgH2 catalysed with NaNH2

To improve hydrogen desorption properties of MgH2, mechanical milling of MgH2 with low concentration (2 and 5%) of NaNH2 has been performed. Pre-milling of MgH2 for 10 h has been done and then six samples have been synthesised with different milling times from 15 to 60 min. Microstructural characterisation has been performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser scattering measurements (PSD), and correlated to desorption properties examined using Differential Scanning Calorimetry (DSC) and Hydrogen Sorption Analyser (HSA). Thermal analysis shows that desorption temperatures are shifted towards lower values. It also highlights the significance of milling time and additive concentration on desorption behaviour.

Mechanical milling of Mg, Ni and Y powder mixture and investigating the effects of produced nanostructured MgNi4Y on hydrogen desorption properties of MgH2

It has been reported that intermetallic compounds could be used to improve hydrogen storage properties of Mg-based alloys. In this study, an attempt was made to synthesize the MgNi4Y compound from pure Ni, Mg and Y elemental powders via the combination of mechanical milling and heat treatment methods. In this regard, powders were ball milled in different conditions and then heat treated at 400 and 600 °C for 4 h to investigate the effect of temperature on the formation of MgNi4Y intermetallic compound. The characteristics of mixtures were evaluated via (XRD) and (SEM) methods. It was found from the results of XRD analysis that ternary intermetallic compound was not formed completely via ball milling alone. Nanostructured intermetallic compound was formed after heat treatment of milled powder at 600 °C for 25 h. Furthermore, addition of 5 and 10 wt% of the produced intermetallic compound to MgH2 decreased hydrogen desorption temperature and increased released hydrogen content.

NiB nanoparticles: A new nickel-based catalyst for hydrogen storage properties of MgH2

In this paper, amorphous NiB nanoparticles were fabricated by chemical reduction method and the effect of NiB nanoparticles on hydrogen desorption properties of MgH2 was investigated. Measurements using temperature-programmed desorption system (TPD) and volumetric pressure–composition isotherm (PCI) revealed that both the desorption temperature and desorption kinetics have been improved by adding 10 wt% amorphous NiB. For example, the MgH2–10 wt%NiB mixture started to release hydrogen at 180 °C, whereas it had to heat up to 300 °C to release hydrogen for the pure MgH2. In addition, a hydrogen desorption capacity of 6.0wt% was reached within 10 min at 300 °C for the MgH2–10 wt%NiB mixture, in contrast, even after 120 min only 2.0 wt% hydrogen was desorbed for pure MgH2 under the same conditions. An activation energy of 59.7 kJ/mol for the MgH2/NiB composite has been obtained from the desorption data, which exhibits an enhanced kinetics possibly due to the additives reduced the barrier and lowered the driving forces for nucleation. Further cyclic kinetics investigation using high-pressure differential scanning calorimetry technique (HP-DSC) indicated that the composite had good cycle stability.

Effects of nano-confinement on the hydrogen desorption properties of MgH2

MgH2 particles were synthesized by wet impregnation within the pores of the mesoporous materials SBA15 and CMK3. XRD and TEM results of Mg/SBA15 compounds revealed MgO surface impurities, indicating non-compatibility of SBA15 for the synthesis of MgH2 particles within SBA15 pores. No impurity phase was detected in Mg/CMK3 compounds. Thermal desorption behavior of MgH2/CMK3 compounds were studied by varying the MgH2 loading amount in CMK3. TPD results of MgH2/CMK3 compounds demonstrated that the onset and maximum hydrogen desorption temperatures were significantly influenced by the MgH2 loading amount. MgH2/CMK3 compounds with 20wt% loading released hydrogen at a temperature of 253°C. Its corresponding decomposition enthalpy was equal to 52.38±2.16kJ/mol H2. Furthermore, TEM images of this sample demonstrated the existence of well-dispersed MgH2 nanocrystallites (d∼4nm) inside the pores of CMK3 template.

Changes of structural and hydrogen desorption properties of MgH2 indused by ion irradiation

Changes in structural and hydrogen desorption properties of MgH2 induced by ion irradiation have been investigated. MgH2 powder samples have been irradiated with 45 keV B3+ and 120 keV Ar8+ions, with ion fluence of 1015 ions/cm2. The effects of ion irradiation are estimated by numerical calculations using SRIM package. The induced material modifications and their consequences on hydrogen dynamics in the system are investigated by XRD, particle size distribution and TPD techniques. Changes of TPD spectra with irradiation conditions suggest that there are several mechanisms involved in desorption process which depend on defect concentration and their interaction and ordering. The results confirmed that the near-surface area of MgH2 and formation of a substoichiometric MgHx (x<2) play a crucial role in hydrogen kinetics and that various concentrations of induced defects substantially influence H diffusion and desorption kinetics in MgH2. The results also confirm that there is possibility to control the thermodynamic parameters by controlling vacancies concentration in the system.