Dehydrogenation Temperature Research Articles

Enhancing performance of microbolometers by utilizing low-temperature polycrystalline silicon

In response to the urgent need for advanced noncontact temperature sensing technologies to mitigate pandemic transmission, there has been a notable surge in global demand. Thermal cameras, combined with infrared sensors, are critical not only for high-resolution imaging but also for cost-effective commercialization. Amorphous silicon-based microbolometers offer advantages in terms of integration and cost compatibility with conventional silicon processes. However, they suffer from limitations in their electrical properties, particularly in the noise-equivalent temperature difference. This study examines the effectiveness of low-temperature polycrystalline silicon (poly-Si) as an active material for microbolometer cells compared to amorphous silicon, focusing on improving the temperature coefficient of resistance (TCR) and lowering the noise density. Our investigation reveals that various parameters, such as dehydrogenation temperatures ranging from 350 to 550 °C, diverse laser annealing techniques (including single, step and multishot methods), and laser power density levels ranging from 150 to 300 mJ/cm2, influence the grain size trends of poly-Si. Using these methods, we produced poly-Si films with grain sizes ranging from 15 to 40 nm, which were used as the active layer in bolometer cells. The final part of our study assessed the TCR and noise density in devices with different poly-Si grain sizes. The TCR/noise density ratio was 3.5 times better in poly-Si devices compared to amorphous silicon devices. This study evaluates poly-Si as an active material for microbolometers, paving the way for future research and development in next-generation infrared sensor technology.

Model catalytic studies on the thermal dehydrogenation of the benzaldehyde/cyclohexylmethanol LOHC system on Pt(111).

We investigated the dehydrogenation reaction and the thermal robustness of the liquid organic hydrogen carrier (LOHC) couple benzaldehyde/cyclohexylmethanol on a Pt(111) model catalyst in situ in synchrotron radiation photoelectron spectroscopy- and complementary temperature-programmed desorption experiments. The system stores hydrogen in a cyclohexyl group and a primary alcohol functionality and achieves an attractive hydrogen storage capacity of 7.0 mass%. We observed a stepwise dehydrogenation mechanism, characterized by a low temperature dehydrogenation of the alcohol group at 235 K. However, stability limitations challenge the system's applicability as reversible hydrogen storage solution, as the resultant aldehyde was found to decompose during the dehydrogenation of its cyclohexyl group (between 250 and 350 K). A comparison of cyclohexylmethanol with the structurally related secondary alcohol (1-cyclo-hexylethanol; 6.3 mass% hydrogen) revealed a parallel stepwise dehydrogenation pattern for both compounds, but a technically relevant superior thermal robustness of the latter. This demonstrates the influence of the alcohol group's substitution degree on the dehydrogenation characteristics of alcohol-functionalized LOHC compounds. Density functional theory calculations are in good agreement with the experimentally observed stability trend.

FeNi3 alloy doped carbon spheres for improving hydrogen storage performance of MgH2

MgH2 is one of the ideal hydrogen storage materials because of its high hydrogen storage density, but the thermodynamic stability and slow kinetics of Mg/MgH2 system hinder its practical application. Transition metal catalyst doping has become an important strategy to improve the hydrogen storage kinetics of MgH2. In this work, FeNi3@CS was prepared by solvothermal method with carbon spheres (CS) as the support, and introduced into Mg/MgH2 system to prepare MgH2–FeNi3@CS composite. The initial dehydrogenation temperature of MgH2–FeNi3@CS composite is 565 K, which is 100 K lower than additive-free MgH2. At 423 K, MgH2–FeNi3@CS composite could absorb 4.5 wt% H2, while the hydrogen absorption capacity of MgH2 without additives is only 2.0 wt%. After 10 cycles, the hydrogenation and dehydrogenation capacity could be maintained at 5.6 wt% and 4.5 wt%, respectively. In addition, the activation energy of MgH2–FeNi3@CS composite decreased by 52 kJ/mol compared with MgH2. FeNi3 was in situ converted to Mg2NiH4 and Fe after hydrogenation-ball milling, which were considered as the catalytic active substances in Mg/MgH2 system. The synergistic catalysis of Mg2Ni/Mg2NiH4, Fe and carbon materials has a positive effect on improving the hydrogen storage performance of Mg/MgH2 system.

Ni/V-MgnHm nanoclusters: Recent advances toward improving the dehydrogenation thermodynamics for efficient hydrogen storage

Understanding the properties of solid-state materials at the nanoscale is a crucial scientific endeavor in the pursuit of a sustainable energy future. Since magnesium hydride is the most practical material for hydrogen storage, research is still ongoing to reduce the enthalpy for dehydrogenation. In this computational theory, we systematically investigated the enthalpy of dehydrogenation of MgnHm nanoclusters of different sizes (0.5–2.8 nm) through density functional theory (DFT) and ab-initio molecular dynamic (AIMD) simulations. Our results revealed that increasing the MgnHm nanocluster size can remarkably improve the formation energy compared to the MgH2-bulk stabilization; the formation energy shifted from −65.12 kJ/mol for (0.5 nm)-MgnHm nanocluster to −51.37 kJ/mol for (2.8 nm)-MgnHm nanocluster. As compared to bulk phase, the lower stability of the nanoclusters indicates that it is much easier to desorb hydrogen from the surface. According to the effects of compressive/tensile strains, (2.8 nm)-MgnHm nanocluster does not improve the dehydrogenation temperature in the desired direction. Unlike metal doping, 9.10%@Ni and 10.14%@V-doped (2.8 nm)-MgnHm nanocluster exhibit formation energies of −47.27 and −46.34 kJ/mol with calculated desorption temperatures of 362.89 and 355.75 K, respectively, which ensures the room temperature applicability of this hydrogen storage material.

Research on the modification of magnesium hydride by two-dimensional layered Mo2Ti2C3 MXene

One of the most important technologies for the sustainable development of energy in the future is solid-state hydrogen storage. This study employed etching methods to fabricate two-dimensional layered catalyst Mo2Ti2C3 MXene, which was compared with unetched MAX phases Mo2Ti2AlC3 and Ti3C2, as well as Mo2C. Through mechanical ball milling, these materials were mixed with MgH2 to prepare composite materials, including MgH2 + Ti2C3, MgH2 + Mo2C, MgH2 + Mo2Ti2AlC3, and MgH2 + Mo2Ti2C3. According to the study, Mo2Ti2C3 demonstrates the synergistic catalytic actions of Ti and Mo in contrast to Ti2C3 and Mo2C. The composite material MgH2 + Mo2Ti2C3 lowers the initial dehydrogenation temperature of MgH2 to 180 °C, which is 165 °C lower than pure MgH2. After 30 min at 250 °C, the dehydrogenation amount is approximately 5.85 wt%. Hydrogen absorption begins at 40 °C and reaches approximately 5.75 wt% at 150 °C. Additionally, it maintains a reversible hydrogen storage capacity of up to 96 % even after 20th cycles at 300 °C. This is because Mo2Ti2C3 has one less layer of Al than Mo2Ti2AlC3, which results in a wider interlayer spacing, more active sites for MgH2, and facilitates hydrogen molecule dissociation and recombination.

In-situ formation of V and Mg2Co/Mg2CoH5 for boosting the hydrogen storage properties of MgH2

Among the potential candidates for solid-state hydrogen storage, magnesium hydride (MgH2) exhibits high storage capacity of 7.6 wt%. However, its commercial application is hindered by the unsatisfactory kinetics properties and stable thermodynamics. In this study, we synthesized porous spherical CoV₂O₆ and incorporated it into MgH2, reducing the initial dehydrogenation temperature of MgH2 to 190 °C. Additionally, rapid hydrogen uptake was also observed, approaching 6.5 wt% H2 within 1000 s at 190 °C. A notable decrease of 45.78 kJ/mol in the apparent activation energy (Ea) for dehydrogenation signifies an improved dehydrogenation kinetic. The formation of Mg2Co/Mg2CoH5, along with the presence of single-valence and multi-valence vanadium, facilitated multiple electron transfer pathways. In particular, vanadium elongated the Mg–H bond is responsible for the high catalytic activity in boosting the hydrogen storage performance of MgH2. These findings provide new intuitions for further research to enhance the kinetic properties of hydrogen adsorption and desorption in magnesium hydride.

The design of Mg–Ti–V–Nb–Cr lightweight high entropy alloys for hydrogen storage

In this study, body-centered-cubic Ti24V18Nb6Cr12 high entropy alloy (HEA) is selected as the matrix to design Mg–Ti–V–Nb–Cr lightweight HEAs. Based on first-principles calculations, the hydrogen storage properties of a series of Mg–Ti–V–Nb–Cr HEAs are systematically investigated. The designed Mg-based HEAs are found to be stable after hydrogenation and exhibit high gravimetric hydrogen storage capacities (HSCs). Particularly, the gravimetric HSC of Mg6Ti24V18Cr12 HEA is as high as 4.091 wt%. Besides, the dehydrogenation temperature of the Mg–Ti–V–Nb–Cr HEAs decreases obviously with increasing Mg content, which results from the weakened bonding strength of <M-H> pairs. This study demonstrates that the Mg6Ti24V18Cr12 HEA is a potential candidate for hydrogen storage.

Enhanced hydrogen kinetics of Mg–Ni–La alloys via slight Y element additive

Alloying represents an effective approach for addressing challenges related to over stable thermodynamics and slow kinetics in magnesium alloys. The incorporation of Y dopant served to enhance the quantity of grain boundaries and phase boundaries, thereby addressing the issue of high dehydrogenation temperature observed in Mg85–Ni10–La5, which can be decreased to 273.3 °C after the addition of 0.5 wt% Y additive. In addition, the initial hydrogenation rate of Mg85–Ni10–La4.5-Y0.5 reached up to 3.42 wt% H2 at 260 °C and the apparent activation energy for dehydriding was decreased from 115.31 to 86.05 kJ/mol. Theoretical calculations suggested that the hydrogen adsorption energy of Mg85–Ni10–La4.5-Y0.5 was dramatically lower than that of Mg85–Ni10–La5, improving hydrogenation properties. The consistency between theoretical calculations and experimental outcomes provided a valuable reference for the selection of suitable magnesium-based hydrogen storage materials.

Effect of hydrogenation on fatigue crack growth resistance of diffusion bonded TC4 titanium alloy laminates

A method was proposed to improve the fatigue crack growth (FCG) resistance of TC4 (Ti6Al4V) titanium alloy laminate by hydrogenation/low-temperature diffusion bonding/dehydrogenation (H-DB-DH) combined process. Effects of hydrogen contents and different dehydrogenation temperatures on FCG behaviors and tensile properties as well as microstructures were investigated. Residual hydrogen contents beneath fatigue fracture surfaces were measured to determine the safe dehydrogenation temperature. The hydrogen content of 0.3 wt% and dehydrogenation temperature of 780 °C are optimal to produce TC4 laminate with a 9.87 % improvement of FCG life compared with the diffusion bonded one without hydrogenation. FCG rate decrease results from the comprehensive effect of recrystallization volume fraction increase, grain refinement, mean geometrically necessary dislocations (GNDs) density decrease and texture intensity weakness as well as texture diversity improvement. This paper provides theoretical support for fatigue property improvement of titanium alloy by hydrogen diffusion bonding process.

Mxene-supported NbVH nanoparticles as efficient catalysts for reversible hydrogen storage in magnesium borohydride

Bimetallic niobium vanadium hydride nanoparticles (NbVH NPs) anchored on Ti3C2 were synthesized using a facile ball milling method as an effective catalyst for the dehydrogenation kinetics and reversibility of Mg(BH4)2. It was found that the onset dehydrogenation temperature of the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite was 105.7 °C and released 9.07 wt% of hydrogen at 330 °C, while undoped Mg(BH4)2 only released 4.2 wt% of H2 from 248 °C to 330 °C. Additionally, the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite achieved remarkable hydrogen release of over 9.44 wt% at a temperature as low as 230 °C, indicating unexpected dehydrogenation kinetics. In the reversible hydrogen desorption tests, Mg(BH4)2 + 30NbVH NPs@Ti3C2 released 5.98 wt% of H2 in the 2nd cycle at 250 °C and maintained a reversible capacity of 4.35 wt% after 10 cycles, demonstrating a remarkable enhancement in reversibility. The enhancement in the dehydrogenation kinetics of Mg(BH4)2 could be attributed to the greatly reduced activation energies from 343 kJ·mol−1 and 138.3 kJ·mol−1 to 103.7 kJ·mol−1 and 124 kJ·mol−1. Investigations on the evaluation of catalyst and Mg(BH4)2 during reversible hydrogen storage have revealed that NbVH NPs actually acted as a “bidirectional hydrogen pump”, facilitating both the hydrogen release and uptake from Mg(BH4)2. This strategy of multi-component hydrides may show a new way to design effective catalysts for solid-state hydrogen storage materials.

Thermodynamic and Kinetic Regulation for Mg‐Based Hydrogen Storage Materials: Challenges, Strategies, and Perspectives

AbstractMg‐based hydrogen storage materials have drawn considerable attention as the solution for hydrogen storage and transportation due to their high hydrogen storage density, low cost, and high safety characteristics. However, their practical applications are hindered by the high dehydrogenation temperatures, low equilibrium pressure, and sluggish hydrogenation and dehydrogenation (de/hydrogenation) rates. These functionalities are typically determined by the thermodynamic and kinetic properties of de/hydrogenation reactions. This review comprehensively discusses how the compositeization, catalysts, alloying, and nanofabrication strategies can improve the thermodynamic and kinetic performances of Mg‐based hydrogen storage materials. Since the introduction of various additives leads the samples being a multiple‐phases and elements system, prediction methods of hydrogen storage properties are simultaneously introduced. In the last part of this review, the advantages and disadvantages of each approach are discussed and a summary of the emergence of new materials and potential strategies for realizing lower‐cost preparation, lower operation temperature, and long‐cycle properties is provided.

Efficient hydrogen absorption and dehydrogenation of synergistically catalyzed Mg10Fe by MoS2 and Y2O3 via one-step synthesis and multistage regulation

To effectively deal with the long preparation period and low hydrogen absorption capacity issue of Mg-based hydrogen storage materials. One-step multistage control strategy and high-pressure hydrogenation have been employed to prepare Mg10Fe-M (M = MoS2 or Y2O3 or both) composites. The phase composition, microstructure, morphology, non-isothermal dehydrogenation thermodynamics and isothermal dehydrogenation kinetics at different milling time (2, 4, 8 h) were explored, and the catalytic hydrogen absorption and discharge mechanism of Mg10Fe–MoS2–Y2O3 was proposed. The addition of MoS2 nanoflowers and Y2O3 powder can synergistically regulate and improve the hydrogenation capacity and dehydrogenation temperature of Mg10Fe. The hydrogen absorption and dehydrogenation of Mg10Fe–MoS2–Y2O3 in short time milling for 2 h are 3.64 wt% and 3.27 wt% respectively. After extending the milling time to 8 h, the thermodynamic and kinetic behavior of Mg10Fe-M (M = MoS2 or Y2O3 or both) is greatly improved. Kinetically, the hydrogenation or dehydrogenation capacity increases significantly, Mg10Fe–MoS2 doesn't need activation, and the hydrogenation capacity reaches 5.42 wt% at 623 K, with a yield of about 85.9 % in 60 min. Thermodynamically, the initial dehydrogenation peak temperature drops to about 310 °C, and the apparent activation energy also decreases significantly, among which Mg10Fe–MoS2–Y2O3 was 91.87 kJ/mol. These are attributed to the fact that MoS2 nanoflowers provide many active sites for H2 adsorption and H atom dissociation. Synchro-efficient synthesis and regulation of Mg-rich composite hydrogen storage materials are expected to shorten the synthesis cycle, improve the hydrogen storage performance, and lay a material foundation for the design and development of solid hydrogen storage devices.

Low-temperature hydrogen release exceeding 7 wt% from LiBH4-mannitol composites

Among conventional hydrogen storage materials, LiBH4 has been regarded as one of the best hydrogen transporters due to its relatively large hydrogen capacities. However, because of its extraordinarily high dehydrogenation temperatures, LiBH4 was not suitable for hydrogen storage due to its stable thermodynamic features. Herein, we present a novel approach to LiBH4 that uses solid-state multi-hydroxyl mannitol as a reactant, regulating hydrogen release below 69.9 °C. More than 7 wt% H2 could be released with ultra-fast rates at 140 °C from the LiBH4-mannitol composite. XRD, FTIR, and SEM tests revealed that the reaction between mannitol (Hδ+) and LiBH4 (Hδ−) to produce hydrogen was accompanied by the generation of large amounts of heat in situ, which further promoted the decomposition of LiBH4 for hydrogen production, exceeding the theoretical dehydrogenation amount of Hδ+- Hδ− reaction. This work indicates possibilities for the development of fast and easy high-capacity hydrogen generation systems based on complex hydrides.

Role of the in situ formed LiAl(NH)2 and LiNH2 in significantly improving the hydrogen storage properties of the Mg(NH2)2-2LiH systems with Li3AlH6 addition

The Mg(NH2)2-2LiH system has attracted considerable interest due to its high hydrogen capacity and low theoretical dehydrogenation enthalpy. However, its practical application is limited by sluggish kinetics due to the slow mass transfer rate and the stable N-H bond. In response to these problems, this study introduced Li3AlH6 into the Mg(NH2)2-2LiH system, leveraging the mutual destabilization effects between lithium alanates and metal amides to attenuate the stability of the N-H bond in Mg(NH2)2. The results show that the Mg(NH2)2-2LiH-0.1Li3AlH6 composite can reversibly desorb/absorb hydrogen up to 4.33 wt% at 140 °C with an initial dehydrogenation temperature of 90 °C. This represents a significant improvement over the pristine sample's capacity of 1.23 wt% under the same conditions. Phase structure analyses reveal that the in situ formed LiAl(NH)2 and LiNH2 particles during ball milling play a crucial role in decreasing the energy required for cleaving the N-H bond, transferring mass, and initiating nucleation. Dehydrogenation curves suggest that the dehydrogenation process follows the Avrami-Erofe'ev equation, signifying that the process is controlled by both nucleation and diffusion processes. A pronounced correlation exists between dehydrogenation kinetic energy barriers and nucleation energy barriers of the dehydrogenation products. This finding implies that future reductions in operating temperature and enhancements of the dehydrogenation rate in the Mg(NH2)2-2LiH system can be achieved by decreasing the nucleation energy barriers of the dehydrogenation products.

Low-Temperature Catalytic Oxidation of Volatile Organic Compounds (VOCs) using Transition Metal Mixed Oxide Catalysts

This paper discusses the modification of MnOx by doping various metals, such as Cu, supported on cordierite honeycomb ceramics, which were easily synthesized by using the impregnation method. The physicochemical properties were comprehensively featured via the BET, XRD, SEM-EDX and H2-TPR techniques. Activity results suggested that the introduction of doping metals significantly enhanced the catalytic performance of Cu1Mn2Ox compared to single metal oxides. Furthermore, in the catalytic oxidation of benzene and toluene, the monolithic Cu1Mn2Ox catalyst demonstrates the best catalytic performance. It was able to completely oxidize the two compounds at 275oC with a reaction velocity (WHSV) of about 18,000 mL/(g•hr) and pollutant concentrations of 7000 ppm and 12000 ppm, respectively. The formation of a Cu-Mn solid solution with spinel Cooper-Manganese structure was thought to be the cause of the excellent catalytic performance of monolithic Cu1Mn2Ox. This resulted in an increase in the amount of adsorbed oxygen species on the surface and a high lattice oxygen mobility. This can improve catalyst reducibility and oxygen species activity, as demonstrated by significantly higher dehydrogenation temperatures of Cu-Mn composite oxides through H2-TPR. Meanwhile, the monolithic Cu1Mn2Ox catalyst showed good stability in 16 hours of testing and cycle ability test and showed great potential in practical application.

Modification research on the hydrogen storage performance of bimetallic oxide Zn2Ti3O8 on MgH2

In this study, flake Zn2Ti3O8, TiO2 and rod ZnO catalysts were successfully synthesized by hydrothermal and calcination methods, and the catalytic performance of the three catalysts for MgH2 was compared. Notably, Zn2Ti3O8 had a significant synergistic enhancement effect on the dehydrogenation temperature and desorption kinetics of MgH2. The experimental results showed that the dehydrogenation of MgH2 + 12 wt% Zn2Ti3O8 composite started at about 195 °C, which was about 150 °C lower than that of pure MgH2. Moreover, at 325 °C, MgH2 released only 3.06 wt% H2 in 20 min, whereas the MgH2 + 12 wt% Zn2Ti3O8 composite released the same amount of hydrogen at 250 °C in 3 min. After complete dehydrogenation, the MgH2 + 12 wt% Zn2Ti3O8 composite initiated hydrogen uptake at 40 °C and absorbed about 6.05 wt% of H2 in 60 min at 200 °C. The hydrogen uptake activation energy and dehydrogenation activation energy of the composites were reduced by 24.56 kJ/mol and 44.67 kJ/mol, respectively, when compared to the pure MgH2. Cycling experiments showed that after 20 cycles, the MgH2 + 12 wt% Zn2Ti3O8 composite maintained good cycling stability and the hydrogen storage capacity was still more than 96 %. Therefore, the composite exhibits excellent catalytic and hydrogen storage properties, and has potential applications in improving the hydrogen release rate and reducing the activation energy.

Effectively enhanced catalytic effect of sulfur doped Ti3C2 on the kinetics and cyclic stability of hydrogen storage in MgH2

Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH2. Herein, the sulfur doped Ti3C2 (S-Ti3C2) was successfully prepared by heat treatment of Ti3C2 MXene under Ar/H2S atmosphere to facilitate the hydrogen release and uptake from MgH2. The S-Ti3C2 exhibited pleasant catalytic effect on the hydriding/dehydriding kinetics and cyclic stability of MgH2. The addition of 5 wt% S-Ti3C2 into MgH2 resulted in a reduction of 114 °C in the starting dehydriding temperature compared to pure MgH2. MgH2 + 5 wt% S-Ti3C2 sample could quickly release 6.6 wt% hydrogen in 17 min at 220 °C, and 6.8 wt% H2 was absorbed in 25 min at 200 °C. Cyclic testing revealed that MgH2 + 5 wt% S-Ti3C2 system achieved a reversible hydrogen capacity of 6.5 wt%. Characterization analysis demonstrated that Ti-species (Ti0, Ti2+, Ti–S, and Ti3+) as active species significantly lowered the dehydrogenation temperature and promoted the re-/dehydrogenation kinetics of MgH2, and sulfur doping can effectively improve the stability of Ti0 and Ti3+, contributing to the improvement of cyclic stability of MgH2. This study provides strategy for the construction of catalysts for hydrogen storage materials.

High cyclic stability and low plateau of Ti2V2Zr/NaH/Al hydrogen storage composite system prepared by ultrasound-assisted ball milling

NaH/Al doped with Ti2V2Zr with the aim of lowering the rehydrogenation pressure, lowering the dehydrogenation temperature, and improving the hydrogenation/dehydrogenation kinetics of NaAlH4. It was found that moderate ultrasonic-assisted wet grinding was beneficial to fine particles efficiently, improved uniformity of particle size, and reduced lattice distortion because its crystalline phase can converge more active hydrogen atoms and reduce the energy barrier of H exchange between the alloy and the matrix, thus improving the comprehensive hydrogen storage performance of the composite systems. It could reversibly store 4.81 wt% of hydrogen and completely hydrogenation under a low hydrogen pressure of 55 atm, its starting and ending dehydrogenation temperatures decrease by 81 and 89 °C, respectively, and the activation energies of the two-step dehydrogenation decrease by 26.7 and 52.7 kJ mol−1 respectively, with a dehydrogenation capacity retention of up to 99.58% over five cycles.

HYDROGEN SORPTION IMPROVEMENT OF NaAlH4 CATALYSED BY K2 SiF6 FOR SOLID STATE HYDROGEN STORAGE

Sodium alanate (NaAlH4) has been recognised as a complex metal hydride that is frequently used as a hydrogen storage material. However, dealing with its poor kinetic characteristics and high decomposition temperatures becomes challenging. This research added potassium hexafluorosilicate (K2SiF6) as a catalyst to reduce the dehydrogenation temperature and improve sorption kinetics compared to the undoped NaAlH4. The dehydrogenation temperature of the NaAlH4 composite with 10 wt.% K2SiF6 addition was determined to be 145°C, a decrease of about 31% compared to 210°C for the undoped NaAlH4. The 10 wt.% K2SiF6-added NaAlH4 samples released roughly 1.77 wt.% hydrogen at 200°C after 60 minutes of dehydrogenation, representing faster dehydrogenation kinetics, but the milled NaAlH4 only produced around 1.39 wt.% of hydrogen. According to Kissinger’s analysis, the apparent activation energy, Ea for the decomposition of NaAlH4 was 87.74 kJ/mol in 1st stage and for NaAlH4 10 wt.% K2SiF6 composite, lowered by 30.45 kJ/mol or 25.8% than as-milled NaAlH4 (118.19 kJ/mol). The enhancement of the dehydrogenation performance of the NaAlH4-K2SiF6 composite can be attributed to the formation of the new phases of KAlF4. These findings might alter the reaction pathway of the composite system and improve its thermodynamic properties. The improvement of dehydrogenation performance and the discovery of the role played by KAlF4 in the dehydrogenation process of the NaAlH4-K2SiF6 composite give us valuable insights for developing and optimising future hydrogen storage materials.

MOF-derived Cu based materials as highly active catalysts for improving hydrogen storage performance of Mg-Ni-La-Y alloys

Higher initial (de)hydrogenation temperature and sluggish kinetics are the main bottlenecks to develop Mg-based hydrogen storage alloys with high hydrogen capacity. One of the effective methods of solving these problems is introducing additives to enhance (de)hydrogenation kinetics and decrease particle sizes to lower (de)hydrogenation temperatures. In this work, Mg85-Ni10-La4.5-Y0.5 alloy doped with Cu@C nanoparticles is prepared, which could enhance (de)hydrogenation kinetics via introducing Cu nanoparticles as a catalyst and reduce the alloy particle sizes via acting as a grinding agent to lower (de)hydrogenation temperature. The results indicate the dehydrogenation temperature of the modified Mg85-Ni10-La4.5-Y0.5 composite could be decreased to 308.5 °C, absorb 4.73 wt% H2 at 220 °C within 1 min and release 5.01 wt% H2 within 4 min at 300 °C. Moreover, the capacity retention could be maintained around 98.8 % after 10 cycles at 300 °C, superior than those of Mg85-Ni10-La4.5-Y0.5 and milled-Mg85-Ni10-La4.5-Y0.5. DFT results and characterizations suggest that in-situ formed Mg2Cu could accelerate the dissociation of Mg-H bonds and the presence of amorphous carbon in Mg-Ni-La-Y-Cu system will further synergistically improve the (de)hydrogenation kinetics of Mg85-Ni10-La4.5-Y0.5. Reduced particle sizes under the aid of carbon frameworks also help introduce boundaries of the particles and shorten hydrogen diffusion pathways.