Hydrogen Capacity Research Articles

Integrating Metal–Organic Frameworks and Polyamide 12 for Advanced Hydrogen Storage Through Powder Bed Fusion

This paper introduces a pioneering approach that combines ex situ synthesis with advanced manufacturing to develop ZIF-67-PA12 Nylon composites with mixed-matrix membranes (MMMs), with the goal of enhancing hydrogen storage systems. One method involves producing MOF-PA12 composite powders through an in situ process, which is then commonly used as a base powder for powder bed fusion (PBF) to fabricate various structures. However, developing the in situ MOF-PA12 matrix presents challenges, including limited spreadability and processability at higher MOF contents, as well as reduced porosity due to pore blockage by polymers, ultimately diminishing hydrogen storage capacity. To overcome these issues, PBF is employed to form PA12 powder into films, followed by the ex situ direct synthesis of ZIF-67 onto these substrates at loadings exceeding those typically used in conventional MMM composites. In this study, ZIF-67 mass loadings ranging from 2 to 30 wt.% were synthesized on both PA12 powder and printed film substrates, with loadings on printed PA12 films extended up to 60 wt.%. ZIF-67-PA12-60(f) demonstrated a hydrogen capacity of 0.56 wt.% and achieved 1.53 wt.% for ZIF-67-PA12-30(p); in comparison, PA12 exhibited a capacity of 0.38 wt.%. This was undertaken to explore a range of ZIF-67 Metal–organic frameworks (MOFs) to assess their impact on the properties of the composite, particularly for hydrogen storage applications. Our results demonstrate that ex situ-synthesized ZIF-67-PA12 composite MMMs, which can be used as a final product for direct application and do not require the use of in situ pre-synthesized powder for the PBF process, not only retain significant hydrogen storage capacities, but also offer advantages in terms of repeatability, cost-efficiency, and ease of production. These findings highlight the potential of this innovative composite material as a practical and efficient solution for hydrogen storage, paving the way for advancements in energy storage technologies.

DFT investigation of thermodynamic, electronic, optical, and mechanical properties of XLiH3 (X= Mg, Ca, Sr, and Ba) hydrides for hydrogen storage and energy harvesting

The present study investigates the hydrogen storage capacity and physical properties of the perovskite hydrides XLiH3 (X = Mg, Ca, Sr, and Ba). The studied compounds MgLiH3, CaLiH3, SrLiH3, and BaLiH3 have lattice constants 3.76, 4.29, 4.64, and 5.04 Å, respectively. These compounds are also observed to be stable in cubic phase under atmospheric pressure and temperature conditions. They have hydrogen storage capacities 8.76 wt%, 5.99 wt%, 3.07 wt%, and 2.03 %, respectively. The SrLiH3 compound has the greatest Debye temperature (θD) of 344.41 K. The analysis of the electronic band structure and density of states reveals that perovskite hydrides have semiconducting characteristics with indirect band gap values of 2.66, 2.34, 1.94, and 1.37 eV, respectively. The materials are semiconductors and have suitable band gaps to be utilized in optical devices. Therefore, the optoelectronic properties of dielectric constants, absorption, and energy loss have been determined to predict the potential of materials for optoelectronic applications. Furthermore, the elastic constants, moduli, and anisotropy are also calculated for the observed materials. The Possion and Pugh ratios indicate these compounds exhibit ductile behaviour and significant anisotropy. Therefore, large values of hydrogen capacities, stabilities, and extraordinary physical behaviour make them important for hydrogen storage systems.

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.

Effect of Nb on hydrogen storage properties of Ti–V–Cr-based alloys

This research investigates the impact of incorporating Nb into Ti–V–Cr-based alloys, with compositions ranging from Ti30-xV35Cr35Nbx (x = 0, 5, 10, 15, and 20 at. %), with the objective of enhancing hydrogen storage properties. Employing a comprehensive approach encompassing design, synthesis, and characterization, the study aimed to develop novel hydrogen storage alloys. Utilizing the CALPHAD method, the alloys were designed to anticipate the formation of multicomponent single-phase structures. Structural and microstructural analyses of the synthesized alloys were conducted using XRD, SEM, and EDS techniques. The hydrogen storage capabilities were evaluated utilizing a Sieverts’ type apparatus. The investigated alloys displayed a singular-phase BCC solid solution, characterized by dendritic microstructures. Notably, the Nb-free alloy, Ti30V35Cr35, demonstrated the highest hydrogen storage capacity, reaching 3.62 wt% (∼1.9 H/M) under 20 bar of H2 at room temperature. Among the Nb-containing alloys, Ti25V35Cr35Nb5 exhibited a capacity of 2.91 wt% (∼1.6 H/M) under identical conditions. Furthermore, the incorporation of Nb up to 10 at. % effectively bolstered cycle durability. This study underscores the presence of an optimal Nb content crucial for achieving the highest hydrogen capacity and cycle durability in these alloys.

The structural, elastic, optoelectronic properties and hydrogen storage capability of lead-free hydrides XZrH3 (X: Mg/Ca/Sr/Ba) for hydrogen storage application: A DFT study

Perovskite hydrides are promising materials for hydrogen capacity application to achieve the US DOE on-board criteria. We have investigated novel perovskite hydrides XZrH3 (X: Mg/Ca/Sr/Ba) for H2 storage and transportation applications. In this study we investigates the physical properties of XZrH3 light materials for solid-state hydrogen storage application by incorporating the DFT framework with the CASTEP code. We have theoretically examined the structural, mechanical, electronic, optical, and hydrogen storage properties of these materials. The selected compounds were fully relaxed and optimized in the cubic phase space group Pm-3 m. Structural phase stability was confirmed through thermodynamic, and mechanical analyses. Mechanical properties, evaluated based on Poisson’s ratio, the Puagh’s ratio, and Cauchy pressure, indicate the ductile behavior with a preference for ionic bonding. The electronic structure analysis reveals the metallic behavior of these materials. Optical calculations were also performed to provide additional insights into the physical properties of H2 compounds. The gravimetric hydrogen storage capacities were calculated as 2.55, 2.25, 1.66, and 1.31 wt% for MgZrH3, CaZrH3, SrZrH3, And BaZrH3 hydrides respectively. The identified properties of XZrH3 suggest that these materials could significantly enhance hydrogen storage systems, with potential integration into existing energy technologies, offering a pathway toward more efficient and sustainable hydrogen-based solutions.

Enhancing the dehydrogenation properties of LiAlH4 through the addition of ZrF4 for solid-state hydrogen storage

Hydrogen energy is emerging as an essential alternative to fossil fuels due to its clean energy profile, generating energy without greenhouse gas emissions. Solid-state hydrogen storage, particularly using complex hydrides like LiAlH4, holds promise due to high hydrogen capacities. However, practical applications of LiAlH4 face obstacles due to slow dehydrogenation kinetics and high decomposition temperatures. This study investigates the catalytic effect of ZrF4 on LiAlH4 to improve hydrogen storage properties. Incorporating 10wt.% ZrF4 has significantly lowered the onset desorption temperature from 160 °C to 80 °C. Desoption kinetic result showed that the addition of 10wt.% ZrF4 can enables the release of 5.6wt.% hydrogen in 120min at 100 °C, which is 50 times faster than in undoped samples. X-ray diffraction analysis indicated that ZrF4 facilitated the in-situ formation of Al3Zr and LiF phases during dehydrogenation, thereby enhancing catalytic efficiency. The desorption activation energies for first two reactions decreased significantly by ~ 16kJ/mol and ~24kJ/mol with ZrF4 doping. These findings suggest that ZrF4 effectively improves the hydrogen storage properties of LiAlH4, positioning it as a potential catalyst for solid-state hydrogen storage systems.

Ni/ZSM‐23 Catalysts: Effect of Impregnating Solvent on the Hydroisomerization of n‐Hexadecane

AbstractBifunctional catalysts are widely used in the hydroisomerization of long‐chain n‐alkanes, which are of great significance in the production of high value‐added chemicals. Herein, the Ni/ZSM‐23‐W and Ni/ZSM‐23‐EG catalysts were prepared using water and ethylene glycol, respectively. The catalysts were characterized using XRD, SEM, TEM, NH3‐TPD, Py–IR, H2‐TPR, H2‐TPD, ICP–OES, and XPS, and their catalytic performance was evaluated by conducting the hydroisomerization of n‐hexadecane as a model reaction. It was revealed that the polarity of the impregnating solvent has a significant impact on the dispersion of Ni nanoparticles. When employing ethylene glycol as a solvent, a strong interaction occurred between NiOx and ZSM‐23 in the Ni/ZSM‐23‐EG catalyst, which facilitated the formation of small‐sized and well‐dispersed Ni nanoparticles. Consequently, the Ni/ZSM‐23‐EG catalyst demonstrated a strong hydrogenation capacity, yielding an impressive 72.9% of iso‐hexadecanes yield.

Developments in world motor vehicle production and the future of hydrogen use in the automotive industry

This article provides an overview of World motor vehicle production and hydrogen utilization technologies for current and future use in the Automotive Industry. Hydrogen is the simplest and most abundant element in the Universe; however it is always combined with other elements. Still, the costs of hydrogen production from its combined elements remain high compared to other energy sources; it is extremely difficult to store onboard, the use of natural gas as a feedstock emits CO2, and there are many technical challenges to overcome with these systems. Many years of research and development, as well as changes to the energy infrastructure, may be required before hydrogen can have a significant impact on Earth energy use. In the very long term, electricity and hydrogen are likely to become the preferred complementary energy vectors. Hydrogen and the fuel cell are complementary and each enables the other. Nowadays, due to their low production costs, hydrogen engines are becoming more and more advantageous over fuel cells and are be-coming more widespread. Ammonia has the potential to be used as a hydrogen carrier, mainly due to its high hydrogen capacity. A significant effort would be needed to develop onboard ammonia cracker systems or direct ammonia fuel cells for vehicles.

Design of air-stabilized Mg-Sc alloy with enhanced hydrogen storage properties via in-situ formation of Sc-hydride in Sc dissolved phase

Severe surface oxidation and slow kinetic rates are the main obstacles which limit the industrial application of Mg-based hydrogen storage alloys. In this work, an attempt is carried out to design and develop the highly active and air-stabilized Mg-Scx (x = 1, 2 and 3 at.%) alloys via an inexpensive and efficient method. The Sc atoms are completely dissolved in the Mg matrix to form single-phase solid solution alloy. At 325 °C and 2.0 MPa hydrogen pressure, Mg-Sc2 alloy exhibits the rapidest absorption rate with the hydrogen capacity of 6.25 wt%. The synergism of lattice distortion induced by Sc-doping and the in-situ formed ScH2 nanoparticles enhance the de/hydrogenation kinetics. After exposed to air for 800 h, almost no MgO can be detected and the hydrogen storage capacity is only reduced by 0.11 wt%, maintaining the initial total capacity more than 98 %. Sc can protect Mg-based alloys from O2 and H2O pollution, which is ascribed to the formation of an oxygen atoms exclusion zone around the solute atoms caused by valence electrons transfer.

Direct mechanochemical synthesis of nano-LiAlH4 promoted by 0.696 wt% TiCl4 catalyst surface-modified Al powder

LiAlH4, known for its high hydrogen capacity and metastable nature, is a promising hydrogen source under mild conditions. However, its reversible regeneration from stable binary dehydrogenation phases (LiH/Al) is thermodynamically and kinetically hindered. By constructing a homogeneous and highly dispersed molecular layer of TiCl4 on the surface of the Al reactant to enhance the kinetics of the multiphase interfacial reaction, we achieved the direct mechanochemical synthesis of nano-LiAlH4, bypassing the intermediate phase Li3AlH6. Using the strong Lewis acidity of Ti4+, TiCl4 was chemically adsorbed onto the surface of the Al powder through Ti-O-Al bonds, with a loading capacity of only 0.696 wt%. The obtained TiCl4 surface-modified Al powder and LiH were hydrogenated by ball milling for 10 h under hydrogen pressure to synthesize nano-LiAlH4, which was then dehydrogenated at room temperature. This indicates that the crucial effects of the catalytic sites were dispersed on the reactant surface to ensure the local environment of the multiphase absorption/desorption hydrogen reaction interface and promote the reaction kinetics.

Evaluation and screening of multivariate metal-organic frameworks for hydrogen storage

Multivariate metal-organic frameworks (MTV-MOFs) are characterized by their unique structural feature of incorporating multiple organic linkers and metal ions into a unified framework. This composite construction bestows MTV-MOFs with a broader spectrum of diverse and intricate properties compared to traditional single-component MOFs. In this study, the performance of 560 MTV-MOFs as hydrogen storage adsorbents has been thoroughly investigated. Firstly, the key structural parameters of materials, including density, pore occupied accessible volume, accessible surface area, and porosity were computed. Then, high-throughput Grand Canonical Monte Carlo (GCMC) simulations were employed to calculate hydrogen adsorption capacity of MTV-MOFs under hydrogen pressures of 100 bar at both 77 K and 298 K. Based on simulated results, the deliverable hydrogen capacity of these MTV-MOFs were deduced under both room temperature conditions (298 K, 97.2 bar → 298 K, 5 bar) and low-temperature conditions (77 K, 100 bar → 160 K, 5 bar). Through high-throughput screening, we identified top ten promising MTV-MOFs with the highest hydrogen storage capacity and conducted in-depth studies on their hydrogen adsorption properties. Furthermore, we developed a multivariate linear regression model to quantitatively predict the relationship between hydrogen adsorption capacity and their structural parameters for these MTV-MOFs. The predictions of this model align closely with the outcomes derived from GCMC simulations. The present study highlights the potential of MTV-MOFs as promising candidates for hydrogen storage applications, thereby providing valuable theoretical insights into the exploration of high-capacity hydrogen storage materials.

Enhance hydrogen storage in lightweight solid-state systems based on Poly(vinylnaphthalene)

This article highlights the potential of poly(2-vinylnaphthalene) (PVN) as a novel light-weight solid-state hydrogen storage system for various applications. With an impressive theoretical gravimetric hydrogen capacity of 5.2 wt.-%, PVN stands out for its attractiveness as a hydrogen carrier. The material possesses advantageous characteristics, including moldability, low toxicity, and ease of storage, making it a promising candidate for both stationary and mobile hydrogen storage applications. Experimental findings demonstrate that PVN can be hydrogenated by up to 76 % utilizing an Ru/Al2O3 catalyst at 250 °C for 24 h. Confirmation of the hydrogenation reaction, which results in poly(2-vinyldecalin), was achieved through characterization techniques such as FTIR, 1H NMR, and spectroscopic ellipsometry. The study of the effects of hydrogen pressure and reaction time identified moderate conditions as favorable, though a further exploration of different catalysts is suggested for optimal conversion. A palladium-based catalyst was employed to release hydrogen from the hydrogenated polymer, demonstrating almost complete reversibility of the hydrogenation of poly(2-vinylnaphthalene) with a dehydrogenation yield of 90 %.

Selective hydrogenation of acetylene over Pd/β-Mo2C catalyst: Experimental and theoretical studies

Molybdenum carbide is a promising support to tune the metal reactivity, which originates from the interaction between metal and support. In this work, Pd/β-Mo2C was prepared using a deposition-precipitation method for selective hydrogenation of acetylene. The high temperature calcination is employed to modulate the interaction between Pd and β-Mo2C. The Pd/β-Mo2C catalyst calcined at 600 °C exhibits significant promotion in selective hydrogenation, which shows 100 % acetylene conversion and 81.4 % ethylene selectivity at 160 °C. The activity promotion originates from the enhanced electronic metal-support interaction, which induces a shift of Pd 3d to higher binding energy. Besides, the Pd species become atomically dispersed after calcination. The changes in geometric and electronic structure suppress the formation of Pd hydrides, which consequently inhibits the excessive hydrogenation capacity of Pd. The structure variation also affects the adsorption of ethylene. No strong adsorbed ethylene (di-σ bonded ethylene) can be identified, which is conducive to the improvement of ethylene selectivity. Density functional theoretical (DFT) calculations confirm that Pd on β-Mo2C is positively charged. The desorption energy of C2H4* (0.78 eV) is significantly lower than that of further hydrogenation (1.45 eV), which explains the improved ethylene selectivity of the calcinated catalyst. The present study indicates calcination is an effective method to tune the activity of Pd/β-Mo2C for reactions beyond selective hydrogenation of acetylene.

Effect of Mn substitution on crystal structure and cyclic property of Y–Ni alloy with superlattice structure

This study investigated the crystal structure, P–C isotherm, and cyclic properties of YNi3. We discovered that hydrogen-induced amorphization (HIA) was appeared in three cycles of P–C isotherm at 303 K, but it was not observed at 273 K. An analysis of the three cycles at 303 K revealed a 55 % decrease in hydrogen capacity as compared to the first cycle. To enhance the hydrogenation properties, Mn was substituted for Ni. X-ray Rietveld refinements on YNi2·7Mn0·3H3.8 reveal that the hydride phase retains the PuNi3-type structure of the original alloy. The values of a, c, the unit cell, the MgZn2-type cell, and the CaCu5-type cell expanded 5.6 %, 9.3 %, 21.9 %, 25.0 %, and 18.8 % from the original alloy. The results indicated that YNi2·7Mn0.3 retained 91 % of its initial hydrogen capacity after three cycles at 303 K. After 120 cycles in the cyclic test, YNi3 and YNi2·7Mn0.3 retained 42 % and 90 % of their initial capacity, respectively. The XRD profile of YNi3 after 120 absorption-desorption cycles revealed significant peak broadening. Similarly, peak broadening was also observed in the XRD profile of YNi2·8Mn0.2 after 120 cycles. In comparison, the XRD profile of YNi2·7Mn0.3 after 120 cycles remained relatively unchanged from its initial state. It was observed that YNi2·7Mn0.3 experienced less lattice strain during hydrogenation than YNi2·8Mn0.2.

Performance of Pd and Pt noble metal impregnated on Lapindo mud-based mesoporous silica on hydrotreatment of waste cooking oil into biogasoline

In the present work, an alternative pathway to produce liquid biogasoline with low aromatic value was done via catalytic hydrotreatment of waste cooking oil (WCO) over noble metal (Pd and Pt) loaded on cost-effective mesoporous silica (MS) synthesized from Lapindo mud. The implementation of 1.82 and 1.53 SiO2/CTAB (cetyltrimethylammonium bromide) weight ratio successfully produced Lp-MS with average diameters of 5.1 (Lp-MS1) and 4.7 nm (Lp-MS2), respectively. The XRD analysis showed a better dispersion for Pt with a considerably smaller particle size and TEM image revealed that while Pt was shown to occupy both external and internal surface of Lp-MS1, Pd was only present on the outer part of Lp-MS2. During the hydrotreatment of WCO using a semi-batch reactor, Pd/Lp-MS2 exhibited a superior deoxygenation and hydrogenation capacity than Pt/Lp-MS1 by generating over 60.9% liquid biofuel with 86.75% selectivity towards gasoline-range hydrocarbon. The liquid product obtained from the catalytic hydrotreatment contained very low aromatic compound (<4%) which was known to be responsible in the emission of harmful gas during fuel combustion. This result can be maintained for at least 4 consecutive runs. This study offers another efficient pathway to produce a cleaner source of energy in the form of biogasoline fuel.

Simulation of hydrogen transportation development path and carbon emission reduction path based on LEAP model - A case study of Beijing-Tianjin-Hebei Region

Hydrogen-fuelled vehicles have attracted significant attention around the world recent years as the main form of hydrogen transportation. Chinese government in September 2020 has introduced corresponding supporting policies. In particular, Beijing-Tianjin-Hebei urban agglomeration is the first batch of pilot cities. To research the development of hydrogen transportation and carbon emission reduction paths in Beijing-Tianjin-Hebei urban agglomeration, we construct LEAP-Beijing-Tianjin-Hebei Urban Agglomeration Hydrogen Transportation model, and simulate it based on the scenario analysis method. The results show that the total hydrogen demand reaches 7,975,860 tonnes in the year 2060. And the freight transportation sector is the largest hydrogen consumer in transportation. For carbon emission reduction, transportation sector under different scenarios could achieve net-zero emission in year 2060, with total emission reduction 431.19 million metric tonnes. We suggest that the promotion of hydrogen transportation should be carried out in stages. Early large-scale development of hydrogen-fuelled vehicles in sectors such as passenger cars and specialized vehicles is not significant in emission reduction, and it is more appropriate to start with medium and large-sized commercial vehicles. Gradually extend to the whole transportation sector after the technology of hydrogen-fuelled vehicles is mature and the supply capacity of clean hydrogen is improved.

2LiBH4-MgH2 System Catalytically Modified with a 2D TiNb2O7 Nanoflake for High-Capacity, Fast-Response, and Long-Life Hydrogen Energy Storage.

To achieve large-scale hydrogen storage for growing high energy density and long-life demands in end application, the 2LiBH4-MgH2 (LMBH) reactive hydride system attracts huge interest owing to its high hydrogen capacity and thermodynamically favorable reversibility. The sluggish dehydrogenation kinetics and unsatisfactory cycle life, however, remain two challenges. Herein, a bimetallic titanium-niobium oxide with a two-dimensional nanoflake structure (2D TiNb2O7) is selected elaborately as an active precursor that in situ transforms into TiB2 and NbB2 with ultrafine size and good dispersion in the LMBH system as highly efficient catalysts, giving rise to excellent kinetic properties with long-term cycling stability. For the LMBH system added with 5 wt% 2D TiNb2O7, 9.8 wt% H2 can be released within 20 min at 400 °C, after which the system can be fully hydrogenated in less than 5 min at 350 °C and 10 MPa H2. Moreover, a dehydrogenation capacity of 9.4 wt% can be maintained after 50 cycles corresponding to a retention of 96%, being the highest reported to date. The positive roles of TiB2 and NbB2 for kinetics and recyclability are from their catalytic nucleation effects for MgB2, a main dehydrogenation phase of LMBH, thus reducing the apparent activation energy, suppressing the formation of thermostable Li2B12H12 byproducts, and inhibiting the hydride coarsening. This work develops an advanced LMBH system, bringing hope for high-capacity, fast-response, and long-life hydrogen energy storage.

Effect of Alloying on the Hydrogen Sorption in Ti–Zr–Mn-Based Alloys. Pt. 1: C14-Type Laves-Phase-Based Alloys

The alloys of the Ti–Zr–Mn system based on the C14-type Laves phase are considered as ones of the most promising materials for safe storage and transportation of hydrogen. These alloys have appropriate parameters for activating the processes of absorption and release of hydrogen, a low cost, and a fairly high cyclic stability. In this work, the microstructure and phase composition of the starting alloys and the crystal structure of the hydrides synthesized from them are studied. Possible ways to reduce the cost of the final products are shown. The fact that changing the method of the alloy fabrication does not significantly affect its hydrogen absorption properties is shown. On the example of the considered alloys, it is shown that, as expected, alloying with an element with a larger atomic radius that forms a stable chemical compound with hydrogen results in an increase in the hydrogen capacity. This is explained by both the increased radius of the tetrahedral interstitial sites, where hydrogen atoms are located after dissolution, and the higher total amount of the element interacting with hydrogen.

Synchronously upgrading of hydrogen storage thermodynamic, kinetics and cycling properties of MgH2 via VTiMn catalyst

To effectively enhance the hydrogen storage performance of MgH2, the multimetallic catalyst VTiMn was triumphantly synthesized by mechanical alloying, and the MgH2-10 wt% VTiMn composite was further fabricated. The results revealed that VTiMn significantly improved the thermodynamic, kinetics and cycle properties of MgH2. Compared with pure MgH2, VTiMn promotes its plateau pressure to increase by 0.16 MPa and the initial desorption temperature to decrease by 47 K, showing obvious thermodynamic instability. Meanwhile, the MgH2-VTiMn composite can adsorb 5.5 wt% H2 within 72 s and release within 1200 s at 523 K. The activation energies of hydrogen absorption and desorption are 30.1 and 90.5 kJ/mol, respectively. After 130 cycles at 598 K, 83 % hydrogen capacity retention can still be achieved. Characterisation indicated that the composite formed a core–shell structure with MgH2 coated on the VTiMn surface. Part of the Mn element in VTiMn diffused into the Mg matrix, accompanied by the precipitation of nanoscale α-Mn particles at high temperature. The improved absorption kinetics can be attributed to the accelerated H atoms diffusion by the microcracks in VTiMn and the phase boundaries provided by the nano-precipitated phase, while the desorption kinetics benefits from the promotion of Mg nucleation and growth by α-Mn. Due to the effect of temperature, the rate-determining steps of the hydrogen absorption and desorption process of the composite at 598 K change from H atoms diffusion and Mg nucleation growth to H atoms surface penetration, respectively. These findings will facilitate a more comprehensive understanding of multimetallic catalysts.

Density functional analysis of structural, mechanical, electronic, and hydrogen storage properties of thermodynamically stable lead-free hydrides [formula omitted](X = Cs, Fr): A perspective of clean energy and fuel

A density functional theory based calculations are performed to investigate structural, hydrogen storage, mechanical, electronic and thermodynamical properties of lead-free hydride perovskites XGeH3 (X=Cs, Fr). The optimized lattice constant and hence volume against the minimum energy is obtained and found to be 4.176 Å and 4.184 Å for CsGeH3 and FrGeH3 respectively. The gravimetric and volumetric hydrogen storage capacity of 1.43% and 1.00%, 72.81(g.H2/L) and 73.21(g.H2/L) for CsGeH3 and FrGeH3 respectively. The density of states and electronic band structure predicted the metallic nature of both hydrides which was affirmed by the Fermi Surfaces. The calculation of Poisson’s, Pugh’s ratio and Cauchy’s pressure suggested their brittle nature. The Debye temperature decreases with the increase of temperature while volume and entropy increase by increasing applied temperature. The present study shows the potential of lead-free hydride perovskites in hydrogen storage applications due to rather suitable gravimetric hydrogen capacity and high stability.