Solid Hydrogen Storage Materials Research Articles

Characteristics of constant pressure dehydrogenation and construction of linear diffusion model for solid hydrogen storage materials: A case study of TiMn1.5 alloy

Solid-state hydrogen storage is considered to be the most promising hydrogen storage technology because of its high volumetric capacity and good security. The process of hydrogenation and dehydrogenation of solid hydrogen storage materials can be characterized by a diffusion kinetic model, which can be used to guide the safe and efficient application of hydrogen storage materials. Currently, experimental study on the dehydrogenation characteristics under constant pressure outer boundary condition has not been carried out methodically, and a simple and reliable diffusion kinetic model under this condition should be established based on the experimental results. In this study, an experimental platform for hydrogen absorption and constant pressure dehydrogenation of solid hydrogen storage materials was independently established. The TiMn1.5 alloy and its interstitial hydrides were taken as the experimental research objects to conduct constant pressure dehydrogenation tests, and the dehydrogenation properties at different temperatures were systematically studied. The results show that the dehydrogenation rate decreases with the increase of testing time. The ultimate capacity of hydrogen release increases first and then decreases with the increasing temperature, reaching the maximum value at 30 °C. It is found that the diffusion coefficient increases linearly with time during constant pressure dehydrogenation process. On this basis, a linear diffusion kinetic model is established. The initial diffusion coefficient D0 calculated by the new model has a quadratic polynomial relationship with temperature, and the increase coefficient α of diffusion coefficient has a linear relationship with temperature. According to the mathematical expressions, the dehydrogenation process of TiMn1.5 alloy at different temperatures can be predicted. The research results can provide theoretical guidance for the safe, efficient and controllable application of hydrogen storage materials.

Performance optimization of hydrogen storage reactors based on PCM coupled with heat transfer fins or metal foams

Metal hydride is a type of solid hydrogen storage material that offers excellent hydrogen absorption and desorption reaction properties. However, there is a strong thermal effect during the reaction process when the materials are applied in reactors. Thus, effective thermal management techniques are crucial for promoting efficient reactions. Prior studies on the subject have shown that phase change materials can be coupled with metal hydride reactors to transfer the reaction heat. To further enhance the transfer of heat and reaction efficiency of the metal hydride reactors based on phase change materials, this study explored heat transfer enhancement methods on the phase change materials side, including adding heat transfer fins and discussing the fin parameters and composite foam metal. The findings of the study showed that in comparison to the reactor without fins, the absorption rate of adding 10 sets of fins can increase by 28%, and as the number of fins increased to 14, this value could increase to 39.4%. The use of Y-shaped fins did not substantially improve the reaction rate, mainly due to the sufficient number of straight fins, and the heat transfer area reaching the limit of the fin enhanced the process of heat transport. Thus, the improved method of using copper foam is further considered. Compared with the reactor with and without fins, the absorption rate of the copper foam coupled reactor is increased by 23.4% and 61.3%, respectively.

Fabrication of V2O3-TiO2-rGO ternary heterojunction composite to enhance the hydrogen storage performance of MgH2

The application prospects of MgH2 as a potential solid hydrogen storage material are limited by its stable thermodynamic properties and slow hydrogenation/dehydrogenation kinetics. In this study, a ternary heterogeneous composite material V2O3-TiO2-rGO (V-T-rGO) was synthesized using the ultrasonic hydrothermal method and doped into MgH2 through ball milling to improve its hydrogen storage performance. The experimental results demonstrated that the MgH2 + V-T-rGO samples exhibit superior hydrogen storage properties compared with single-doped V2O3, TiO2, rGO or V-T materials. Specifically, it can uptake hydrogen at room temperature, and adsorbs 5.00 wt% H2 in just 4 min at 150 °C, and releases 5.87 wt% H2 within 6 min at 325 °C, demonstrating a faster reaction rate and successful hydrogen absorption. Additionally, the hydrogenation/dehydrogenation activation energies of MgH2 + V-T-rGO samples are measured at 27.1/72.3 kJ·mol−1, representing a reduction of 51.2/59.2 kJ·mol−1 compared to MgH2 alone. Mechanistic analysis revealed that the multiphase composite system produced synergistic catalytic effects, providing abundant active sites and hydrogen diffusion channels to enhance the hydrogen storage performance of MgH2. This study presents an innovative approach for constructing transition metal oxide heterostructured materials and holds significant reference value for applications in the field of hydrogen storage.

Ternary Fe–Ni–B particles supported on Cu(OH)2–Cu foam: A highly efficient and stable catalyst for hydrolysis of ammonia borane

Ammonia borane (NH3BH3) as a solid chemical hydrogen storage material with a high hydrogen content can be hydrolyzed under mild conditions to release hydrogen. In this work, Fe–Ni–B/Cu(OH)2–Cu foam was synthesized by combining in situ growth and electroless plating. Compared with the binary Fe–B/Cu(OH)2–Cu foam and Ni–B/Cu(OH)2–Cu foam prepared by the same method, the ternary Fe–Ni–B/Cu(OH)2–Cu foam has superior catalytic performance. The Fe–Ni–B/Cu(OH)2–Cu foam catalyst was able to achieve a maximum hydrogen production rate of 5.6 ml min−1 cm−2 at 298 K with an activation energy as low as 46.3 kJ mol−1. And more importantly, its catalytic efficiency has hardly decayed after ten cycles. These excellent properties are due to its low activation energy and the large specific surface, multi–site Cu(OH)2–Cu–foam carrier.

ZIF‐8 decorated FeMo nanoparticles: H2 Production from the catalytic hydrolysis of ammonia‐borane

AbstractAmmonia‐Borane (AB) is considered a promising solid hydrogen storage material due to its high hydrogen content (19.6 wt%) and its use for safe hydrogen transport. The most effective way to produce H2 from AB is to perform the hydrolysis reaction in the presence of a suitable catalyst. In this study, Fe0.2Mo0.8/ZIF‐8 nanocatalyst was synthesized in two steps: (i) synthesis by following the colloidal synthesis technique by thermal decomposition of Mo(CO)6 and Fe(acac)3 in the presence of OM and ODE at high temperatures, and (ii) the resulting colloidal Fe0.2Mo0.8 NPs were decorated into ZIF‐8. The as‐prepared Fe0.2Mo0.8/ZIF‐8 catalyst was identified using advanced characterization techniques such as ICP‐OES, P‐XRD, SEM, SEM–EDX, TEM, TEM‐EDX, XPS, and BET. The catalytic activities of the Fe0.2Mo0.8/ZIF‐8 catalyst in the hydrolysis of AB were investigated in different parameters (temperature, catalyst [Fe0.2Mo0.8] and substrate [H3NBH3] concentration, and recyclability). The results show that high crystallinity Fe0.2Mo0.8 NPs with a uniform 1.31 ± 0.13 nm distribution were formed on the ZIF‐8 surface. Fe0.2Mo0.8/ZIF‐8 catalyst provides a maximum H2 generation rate of 184.2 mLH2 (g catalyst)−1 (min)−1 at 343 K. This uniquely cost‐effective, active and durable Fe0.2Mo0.8/ZIF‐8 catalyst has strong potential for H2‐based fuel cell (PEM: Proton Exchange Membrane) applications where AB is a suitable H2 carrier.Highlights FeMo NPs were synthesized by a colloidal synthesis method and decorated into ZIF‐8. FeMo/ZIF‐8 catalyst is an active catalyst in the hydrolysis of AB. FeMo/ZIF‐8 catalyst showed an initial TOF value of 449.85 mol(H2)·molFe0.2Mo0.8−1·h−1 in the AB hydrolysis at 338 K.

A novel carbon-induced-porosity mechanism for improved cycling stability of magnesium hydride

MgH2 has been extensively studied as one of the most ideal solid hydrogen storage materials. Nevertheless, rapid capacity decay and sluggish hydrogen storage kinetics hamper its practical application. Herein, a Ni/C nano-catalyst doped MgH2 (MgH2Ni/C) shows an improved hydrogen absorption kinetics with largely reduced activation energy. Particularly, the MgH2Ni/C displays remarkable cycling stability, which maintains a high capacity of 6.01 wt% (98.8 % of initial capacity) even after 50 full hydrogen ab/desorption cycles, while the undoped MgH2 counterpart retains only 85.2 % of its initial capacity. Detailed microstructure characterizations clearly reveal that particle sintering/growth accounts primarily for the deterioration of cycling performance of undoped MgH2. By comparison, MgH2Ni/C can maintain a stable particle size with a growing porous structure during long-term cycling, which effectively increases the specific surface of the particles. A novel carbon-induced-porosity stabilization mechanism is proposed, which can stabilize the proportion of rapid hydrogen absorption process, thus dominating the excellent cycling performance of MgH2Ni/C. This study provides new insights into the cycling stability mechanism of carbon-containing Mg-based hydrogen storage materials, thus promoting their practical applications.

Dipole-induced hydrogen bonds enhanced P/O co-doped Lyocell-based porous carbon fiber cloth for hydrogen storage under ambient pressure

Currently, the hydrogen storage application of carbon-based adsorbent materials is mostly implemented under the pressure conditions of 30–300 bar, while there is few targeted studies conducted on the unsaturated adsorption under ambient pressure conditions. Therefore, based on industrialized Lyocell biopolymer fiber precursors and the enhancement effects of dipole-induced hydrogen bonds (DIHB), this work presents a facile construction strategy for P/O co-doped Lyocell-based porous carbon fiber cloth (Ly-ACF-F40). By the technical route of thermal stabilization---sonication assisted phosphoric acid activation---hydrogen bonds introduced by interfacial fluorination, the constructed Ly-ACF-F40 acquires a high specific surface area (1870 m2/g) and total pore volume (1.277 cm3/g), and an excellent hydrogen storage capacity of 3.22 wt% under ambient pressure conditions (77 K, 1 bar). The study directly demonstrated in the experiment that dipole induced hydrogen bonding H(I)-H(II)···F can effectively enhance the atmospheric hydrogen storage density on the basis of other eliminating influencing factors of specific surface area. The simple construction strategy of porous carbon-based materials can provide reference for the research of unsaturated adsorption hydrogen storage materials under ambient pressure conditions, also assist in the application and promotion of low-cost solid hydrogen storage materials.

Research Progress of Hydrogen Storage Materials

Hydrogen energy has become increasingly popular as a clean and renewable source of energy in recent years due to the high levels of carbon pollution worldwide. This essay examines the current research status on various hydrogen storage techniques and materials for hydrogen energy. There are currently three primary hydrogen storage methods: high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage, and solid-state hydrogen storage. The most widely employed method in China is high-pressure gaseous hydrogen storage. It entails compressing hydrogen fuel into a container under high pressure. As a result, high-pressure gaseous hydrogen storage is commonly used for stationary hydrogen storage. Low temperature liquid hydrogen storage involves compressing the hydrogen at first and then cooling it down with liquefaction technology. However, due to the strict requirements for compression and container insulation, its actual performance is often limited. This paper focuses on the study of solid hydrogen storage materials. The physical adsorption materials that are successively introduced include carbon-based hydrogen storage materials, metal-organic frameworks (MOFs), and Covalent organic frameworks (COFs). In the current study, carbon-based hydrogen storage materials show better performance only in low-temperature and high-pressure environments, but MOFs and COFs have great prospects in hydrogen storage. The chemical absorption hydrogen storage materials introduced in this paper are metal alloy hydrogen storage and hydrogenation complexes hydrogen storage, mainly rare earth-based hydrogen storage materials and magnesium-based hydrogen storage materials. Among them, magnesium-based hydrogen storage materials have become one of the most promising hydrogen storage materials due to their low cost and good hydrogen storage performance.

Key technology and application of AB2 hydrogen storage alloy in fuel cell hydrogen supply system

At present, there is limited research on the application of fuel cell power generation system technology using solid hydrogen storage materials, especially in hydrogen-assisted two-wheelers. Considering the disadvantages of low hydrogen storage capacity and poor kinetics of hydrogen storage materials, our primary focus is to achieve smooth hydrogen ab-/desorption over a wide temperature range to meet the requirements of fuel cells and their integrated power generation systems. In this paper, the Ti0.9Zr0.1Mn1.45V0.4Fe0.15 hydrogen storage alloy was successfully prepared by arc melting. The maximum hydrogen storage capacity reaches 1.89 ​wt% at 318 ​K. The alloy has the capability to absorb 90% of hydrogen storage capacity within 50 ​s at 7 ​MPa and release 90% of hydrogen within 220 ​s. Comsol Multiphysics 6.0 software was used to simulate the hydrogen ab-/desorption processes of the tank. The flow rate of cooling water during hydrogen absorption varied in a gradient of (0.02 ​+ ​x) m s−1 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12). Cooling water flow rate is positively correlated with the hydrogen absorption rate but negatively correlated with the cost. When the cooling rate is 0.06 m s−1, both simulation and experimentation have shown that the hydrogen storage tank is capable of steady hydrogen desorption for over 6 h at a flow rate of 2 L min−1. Based on the above conclusions, we have successfully developed a hydrogen-assisted two-wheeler with a range of 80 km and achieved regional demonstration operations in Changzhou and Shaoguan. This paper highlights the achievements of our team in the technological development of fuel cell power generation systems using solid hydrogen storage materials as hydrogen storage carriers and their application in two-wheelers in recent years.

Computational evaluation of comprehensive properties of MgX3H8 (X = Sc, Ti and Zr) as effective solid state hydrogen storage materials

In this study, structural, mechanical, electronic, dynamic, thermodynamic and hydrogen storage properties of MgX3H8 (X = Sc, Ti, Zr) were investigated by means of density functional theory which was not studied/reported experimentally or theoretically in the previous literature. This is the first thorough study about various properties of these materials. These materials were considered as promising potential host materials for solid state hydrogen storage. The evaluation of computed formation enthalpies of MgX3H8 (X = Sc, Ti, Zr), elastic constants, and phonon dispersion graphs revealed that MgX3H8 (X = Sc, Ti, Zr) is thermodynamically, mechanically, and dynamically stable and synthesizable. The analysis of B/G ratio, Cp and Poisson's ratio showed that MgSc3H8 is a brittle material whereas MgTi3H8 and MgZr3H8 are ductile materials. Moreover, anisotropy factor, machinability index, hardness, melting and Debye temperature of the materials were obtained and analysed in depth. The electronic band structures of MgX3H8 (X = Sc, Ti, Zr) illustrated metallic character since the bands (valence and conduction) intersect the Fermi level along the main symmetry directions. The phonon dispersion curves, and the partial state densities of the materials have positive frequencies, therefore, materials are dynamically stable in the cubic structure. The gravimetric hydrogen densities were calculated as 4.60 wt% for MgSc3H8, 4.38 wt% for MgTi3H8 and 2.56 wt% for MgZr3H8. The hydrogen desorption temperatures were computed as 239.54 K for MgSc3H8, 241.76 K for MgTi3H8 and 303.87 K for MgZr3H8. The mechanical properties of the materials suggest that they can be promising host materials for hydrogen storage.

Cerium-Organic Framework (CeOF) for hydrogen generation via the hydrolysis of NaBH4

Hydrogen gas has been considered an eco-friendly energy source with a high energy content, making it a suitable energy carrier for several industries. A cerium-organic framework, denoted as CeOF, was synthesized by reacting cerium with a tricarboxylic organic linker using a solvothermal method. The material's characteristics were analyzed using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier transforms infrared spectroscopy (FT-IR) to confirm its crystallinity, phase purity, elemental composition, chemical bonding, morphology, and thermal stability. CeOF catalysized the release of hydrogen from solid hydrogen storage materials, e.g., sodium borohydride (NaBH4) by the reaction with water via hydrolysis. An examination was carried out to analyze the influence of catalyst loading, NaBH4 weight (0.2–3 wt.%), and reaction temperature. The CeOF catalyst showed a significant hydrogen generation rate (HGR) of 1800 mLH2·gcat-1·min−1, with an activation energy of 58.8 kJ·mol−1. It showed good catalytic recyclability enabling continuous hydrogen production for four cycles without any significant decrease in the material’s performance.

Magnesium based multi-metallic hybrids with soot for hydrogen storage

Magnesium hydride is one of the most sought-after materials for solid state hydrogen storage due to its low cost and high gravimetric capacity (7.6 wt% hydrogen). However, high temperature of desorption (>350 °C) and slow kinetics limit its use for commercial on-board applications. In this work, accumulative roll bonding (ARB) technique has been utilized to synthesise Mg–LaNi5–Mg2Ni-soot hybrid with enhanced hydrogen storage properties. It is seen that the hybrid absorbs ∼6.2 wt% hydrogen at a plateau pressure of ∼2 bar at 300 °C and exhibits fast kinetics with ∼6.6 wt% hydrogen absorption within ∼30 min at 300 °C and 20 bar hydrogen pressure. The role of Mg2Ni as a catalyst as well as hydrogen absorbing medium provides an effect akin to ‘hydrogen pump’, thus enhancing the rate of hydrogen absorption. Presence of carbon in various forms such as aciniform, carbonaceous microgel and cenospheres (derived from soot) plays a vital role by providing channels for diffusion of hydrogen through the hybrid. The ARB technique provides an inexpensive and scalable method of synthesis of Mg based hybrids with large number of interfaces and high amount of strain leading to enhanced hydrogen storage properties.

High-capacity hydrogen storage in lithium decorated penta-BN2: A first-principles study

The development of solid hydrogen storage materials is an important part of the large-scale application of hydrogen energy. The gravimetric density of hydrogen storage materials and modified metal atoms agglomeration are the key research issues in two-dimensional hydrogen storage materials. Based on first-principles calculations, lithium-modified penta-BN2(P-BN2) is developed as a new hydrogen storage material. The geometric and electronic structures of lithium-modified P-BN2 (Li-P-BN2) have been calculated. P-BN2 has strong binding ability to lithium metal atoms, preventing the formation of lithium metal clusters, and the material has a strong stability. Twenty-eight hydrogen molecules can be stably adsorbed by the Li-P-BN2 system, and the theoretical storage gravimetric density of hydrogen is 13.27 wt%. Ab initio molecular dynamics (AIMD) shows that the material has a useable capacity of 8.95 wt% at 300 K. The mean desorption temperature is 437.13 K. The excellent hydrogen adsorption capacity and high gravimetric density of Li-P-BN2 may make it a promising hydrogen storage material.

Improved hydrogen storage properties of MgH2 by Mxene (Ti3C2) supported MnO2

MgH2 is a promising high-capacity solid hydrogen storage material. In this work, MnO2-doped Ti3C2 (Ti3C2@MnO2) was synthesized and used as a catalyst to improve the hydrogen storage performance of MgH2. We found that the dehydrogenated 10 wt% Ti3C2@MnO2-doped MgH2 sample exhibited good hydrogen adsorption ability even at room temperature (30 °C), and could absorb 5.13 wt% of hydrogen in 400 s at 75 °C. The re‑hydrogenated Ti3C2@MnO2-doped MgH2 sample started to release hydrogen at 182 °C and required 484 s to completely release hydrogen at 275 °C with a dehydrogenation capacity of 6.4 wt%. The Ti3C2@MnO2 composite did not change the thermodynamic properties of MgH2. In the MgH2 + Ti3C2@MnO2 sample, Ti3C2, TiO2, MnO2, MnO, and Mn combined with MgH2 to form Ti3C2/MgH2, TiO2/MgH2, MnO2/MgH2, MnO/MgH2, and Mn/MgH2 multiphase interfaces, which improved the hydrogen storage performance of MgH2. The findings of this work may provide a new strategy for preparing novel and efficient catalysts for hydrogen storage applications.

Preparation of rice husk-based carbon supported ruthenium catalyst for the hydrolysis of ammonia borane to produce hydrogen

An efficient dehydrogenation catalyst is crucial for the application of ammonia borane (NH3BH3, AB) as a solid chemical hydrogen storage material. In this work, a kind of nitrogen-doped rice husk activated carbon (N-RHC) was prepared by roasting melamine and rice husk at high temperature under nitrogen atmosphere. With N-RHC as the support, the rice husk-based carbon supported ruthenium catalyst (Ru/N-RHC) was prepared through impregnation with the RuCl3 solution and its catalytic performance in the hydrolysis of ammonia borane to produce hydrogen was investigated. The results indicate that the Ru/N-RHC catalyst with a Ru loading of 5% performs excellently in the hydrolysis of ammonia borane; the reaction turnover frequency (TOF) reaches 83.71 min−1 and the apparent activation energy decreases from 88.9 to 64.9 kJ/mol under light irradiation. In addition, the hydrogen production rate is positively correlated with the content of ammonia borane and catalyst.

Catalytic mechanisms of nickel nanoparticles for the improved dehydriding kinetics of magnesium hydride

MgH2, albeit with slow desorption kinetics, has been extensively studied as one of the most ideal solid hydrogen storage materials. Adding such catalyst as Ni can improve the desorption kinetics of MgH2, whereas the catalytic role has been attributed to different substances such as Ni, Mg2Ni, Mg2NiH0.3, and Mg2NiH4. In the present study, Ni nanoparticles (Ni-NPs) supported on mesoporous carbon (Ni@C) have been synthesized to improve the hydrogen desorption kinetics of MgH2. The utilization of Ni@C largely decreases the dehydrogenation activation energy from 176.9 to 79.3 kJ mol−1 and the peak temperature of dehydrogenation from 375.5 to 235 °C. The mechanism of Ni catalyst is well examined by advanced aberration-corrected environmental transmission electron microscopy and/or x-ray diffraction. During the first dehydrogenation, detailed microstructural studies reveal that the decomposition of MgH2 is initially triggered by the Ni-NPs, which is the rate-limiting step. Subsequently, the generated Mg reacts rapidly with Ni-NPs to form Mg2Ni, which further promotes the dehydrogenation of residual MgH2. In the following dehydrogenation cycle, Mg2NiH4 can rapidly decompose into Mg2Ni, which continuously promotes the decomposition of MgH2. Our study not only elucidates the mechanism of Ni catalyst but also helps design and assemble catalysts with improved dehydriding kinetics of MgH2.

Highly active bimetallic MOF derivatives for improving the dehydrogenation performance of LiAlH4

LiAlH4 is considered an effective hydrogen storage material due to its high hydrogen storage capacity and relative abundance of aluminum. However, LiAlH4 presents disadvantages such as slow kinetics, high dehydrogenation temperature, and poor reversibility. To improve these shortcomings of LiAlH4, we designed and prepared Ni-Ti bimetallic metal-organic framework derivatives with stable structures and high dispersion of metal species, which named as Ni-Ti-NC. A series of tests show that the composite components and circular disk-like structure of Ni-Ti-NC can improve the dehydrogenation behavior of LiAlH4. Benefiting from the addition of Ni-Ti-NC, the initial decomposition temperature of LiAlH4 significantly decreased to 59.5 ℃, and about 6.11 wt% of hydrogen was rapidly released within 25 min at 200 ℃. Meanwhile, the activation energies of the two-step hydrogen evolution reaction decreased to 64.18 kJ·mol−1 and 73.99 kJ·mol−1, respectively. Furthermore, compared with only 0.09 wt% hydrogen absorption of pure LiAlH4 at 30 bar hydrogen pressure and 300 ℃ constant temperature, doping Ni-Ti-NC promoted the hydrogen absorption capacity of LiAlH4 to nearly 0.64 wt% under the same conditions. In addition, the structure and chemical changes of LiAlH4 after the addition of Ni-Ti-NC were investigated in detail. The reasons why Ni-Ti-NC improved the hydrogen storage performance of LiAlH4 were comprehensively analyzed, which helped us design efficient catalysts for solid hydrogen storage materials.

Effect of electronic alteration on hydrogen storage and optical response in NaMgF3 using DFT approach

Due to the depletion of non-renewable fossil fuels, energy production and storage is a matter of concern for scientific community. Hydrogen being environmental friendly was presented by the scientists a fruitful replacement of fossil fuel, but the storage of hydrogen is still a matter of concern. Safety concerns are associated with hydrogen as an alternative fuel because it is difficult to store and transport. Perovskite materials have attracted researchers as new materials for solid hydrogen storage. In this present work, Density Functional Theory (DFT) calculations have been performed for perovskite NaMg F3−xHx with the GGA-PBE formalism as implemented in the CASTEP code. The aim of the work is to investigate the structural, electronic and optical properties of NaMg F3−xHx perovskite hydride material for hydrogen storage applications with varying substituent concentrations (x = 0, 0.3, 0.6, 0.9, 1.2). The formation enthalpy of the studied material for each concentration reveals that these compounds are stable and synthesizable experimentally. The hydrogen inclusion in pristine material affects the electronic states significantly which is elaborated using band structure and density of states plots. After Hydrogen inclusion, change in density of states has been observed and the band gap is decreased from 5.74eV to 3.311eV. The alteration of electronic band gap directly influences the optical behavior of the material, thus optical response such as dielectric function, absorption and refractive index was also calculated. For hydrogen storage application, gravimetric storage capacity (Cwt%) was calculated for all concentrations of hydrogen inclusion. The value varied from 0.30% to 1.87%, indicating that the presented material is an efficient material not only for opto-electronic applications but also for the hydrogen storage applications.

Local electronic structure of interstitial hydrogen in MgH2 inferred from muon study

Magnesium hydride has great potential as a solid hydrogen (H) storage material because of its high H storage capacity of 7.6 wt%. However, its slow hydrogenation and dehydrogenation kinetics and the high temperature of 300 ∘C required for decomposition are major obstacles to small-scale applications such as automobiles. The local electronic structure of interstitial H in MgH2 is an important fundamental knowledge in solving this problem, which has been studied mainly based on density functional theory (DFT). However, few experimental studies have been performed to assess the results of DFT calculations. We have therefore introduced muon (Mu) as pseudo-H into MgH2 and investigated the corresponding interstitial H states by analyzing their electronic and dynamical properties in detail. As a result, we observed multiple Mu states similar to those observed in wide-gap oxides, and found that their electronic states can be attributed to relaxed–excited states associated with donor/acceptor levels predicted by the recently proposed ‘ambipolarity model’. This provides an indirect support for the DFT calculations on which the model is based via the donor/acceptor levels. An important implication of the muon results for improved hydrogen kinetics is that dehydrogenation, serving as a reduction for hydrides, stabilises the interstitial H− state.

Construction of PAN-based activated carbon nanofibers for hydrogen storage under ambient pressure

Adsorption agents are an important class of solid hydrogen storage materials. Attributed to their high specific surface area and adjustable nanopore structure, activated carbon nanofibers have attracted extensive attention in the application of solid hydrogen storage. The research in this field mostly focuses on applications with a hydrogen pressure condition of 30 to 300 bar, while there have been few systematic studies on the hydrogen storage performance of these materials under ambient pressure. In this study, polyacrylonitrile-based activated carbon nanofibers were constructed by electrospinning technology and ultrasonic-assisted activation technology for the application of atmospheric hydrogen storage. Their nanopore structure was revealed to be mainly composed of micropores, and the relative contents of micropore volume and ultramicropore volume were 77.92% to 88.3% and 22.34% to 24.68%, respectively. Attributed to the synergy of rich microporous structure and surface chemical structure, the atmospheric hydrogen storage density of activated carbon nanofibers could reach 2.64 wt% at 77 K and 1 bar. After the optimization analysis of adsorption isotherm models, the Multisite-Langmuir model was found as more suitable for accurately describing the atmospheric hydrogen adsorption process of activated carbon nanofibers. Cited as: Yu, J., Lin, T., Li, J., Zhang, W., Bao, W., Zhu, B. Construction of PAN-based activated carbon nanofibers for hydrogen storage under ambient pressure. Capillarity, 2023, 6(3): 49-56. https://doi.org/10.46690/capi.2023.03.02