Hydrogen Desorption Mechanism Research Articles

Bridging Materials and Analytics: A Comprehensive Review of Characterization Approaches in Metal-Based Solid-State Hydrogen Storage

The advancement of solid-state hydrogen storage materials is critical for the realization of a sustainable hydrogen economy. This comprehensive review elucidates the state-of-the-art characterization techniques employed in solid-state hydrogen storage research, emphasizing their principles, advantages, limitations, and synergistic applications. We critically analyze conventional methods such as the Sieverts technique, gravimetric analysis, and secondary ion mass spectrometry (SIMS), alongside composite and structure approaches including Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). This review highlights the crucial role of in situ and operando characterization in unraveling the complex mechanisms of hydrogen sorption and desorption. We address the challenges associated with characterizing metal-based solid-state hydrogen storage materials discussing innovative strategies to overcome these obstacles. Furthermore, we explore the integration of advanced computational modeling and data-driven approaches with experimental techniques to enhance our understanding of hydrogen–material interactions at the atomic and molecular levels. This paper also provides a critical assessment of the practical considerations in characterization, including equipment accessibility, sample preparation protocols, and cost-effectiveness. By synthesizing recent advancements and identifying key research directions, this review aims to guide future efforts in the development and optimization of high-performance solid-state hydrogen storage materials, ultimately contributing to the broader goal of sustainable energy systems.

Supported Ruthenium Single-Atom and Clustered Catalysts Outperform Benchmark Pt for Alkaline Hydrogen Evolution.

Guaranteeing satisfactory catalytic behavior while ensuring high metal utilization has become the problem that needs to be addressed when designing noble metal based catalysts for electrochemical reactions. Here, the well-dispersed ruthenium (Ru) based clusters with adjacent Ru single atoms (SAs) on layered sodium cobalt oxide (Ru/NC) is demonstrated to be a superb electrocatalyst for alkaline HER. The Ru/NC catalyst manifests an activity increase by a factor of two relative to the commercial Pt/C. Operando characterizations in conjunction with density functional theory (DFT) simulations uncover the origin of the superior activity and establish a structure-performance relationship, that is, under HER condition, the real active species are Ru SAs and metallic Ru clusters supported on the NC substrate. The excellent alkaline HER activity of the Ru/NC catalyst can be understood by a spatially decoupled water dissociation and hydrogen desorption mechanism, where the NC substrate accelerates the water dissociation rate, and the generated H intermediates would then migrate to the Ru SAs or clusters and recombine to have H2 evolution. More importantly, comparing the two forms of Ru sites, it is the Ru cluster that dominates the HER activity. This article is protected by copyright. All rights reserved.

A brief review of characterization techniques with different length scales for hydrogen storage materials

Increasing environmental pollution and energy consumption have increased the demand for renewable and clean energy. Hydrogen storage materials have attracted increasing attention owing to the large volumetric density of hydrogen storage and high safety, which are beneficial for large-capacity and long-term energy storage capability. Various characterization approaches with different length scales have been conducted to understand the mechanisms of hydrogen absorption and desorption in these materials. In particular, local characterization techniques have been recently applied to study the surface and nanostructural interface effects of these materials because these features can affect hydrogen storage properties. In this article, we review the application of these characterization techniques in exploring hydrogen storage materials.

Density functional theory on reaction mechanism between p-doped LiNH<sub>2</sub> clusters and LiH and a new hydrogen storage and desorption mechanism

Hydrogen energy is considered a clean energy with great development prospects. In the field of hydrogen energy applications, the solid-state chemical hydrogen storage method using hydrogen storage materials as media has received widespread attention due to its safety and high hydrogen storage density. In the research on metal-N-H system hydrogen storage materials, current studies focus on improving the kinetic conditions for hydrogen storage. In this study, the B3LYP hybrid functional method of density functional theory is used to investigate the reaction mechanism between P-doped LiNH<sub>2</sub> clusters and LiH at a cluster level, and explore the effects of doping, in addition a new hydrogen storage mechanism called “secondary hydrogen transfer” is proposed. The full-geometry optimization of (LiNH<sub>2</sub>)<sub><i>n</i></sub> (<i>n</i> = 1–4) clusters and their P-doped clusters at the 6-31G(d,p) basis set level are carried out, and their corresponding most stable configurations are obtained. The distribution and stability of the frontier orbitals of the relevant reactants are calculated. Using the same method and basis set, the theoretical calculation and analysis of the reaction mechanism between P-doped (LiNH<sub>2</sub>)<sub><i>n</i></sub> (<i>n</i> = 1–4) clusters and LiH are conducted, including the configuration optimization of the stationary points in each reaction path, and the correctness of the connection between the stationary points is determined through frequency and intrinsic reaction coordinate calculations. The results show that P doping has a small effect on the lowest unoccupied molecular orbital, while the highest occupied molecular orbital has a significant transition towards the doping atom, and the electron-deficient region is concentrated at the P atom. P doping reduces the stability of the lithium amide clusters and enhances their ability to participate in chemical reactions and reaction activity, and the reaction dehydrogenation energy barrier decreases. The reaction dehydrogenation energy barrier between P-doped LiNH<sub>2</sub> clusters and LiH is significantly lower than that between LiNH<sub>2</sub> and LiH, which is consistent with the analysis of reactant stability. Additionally, it is found that the reaction between P-doped LiNH<sub>2</sub> clusters and LiH tends to dehydrogenate through the —PH<sub>2</sub> functional group and store hydrogen at the —NH<sub>2</sub> functional group. Therefore, a new idea of “secondary hydrogen transfer” is proposed, in which effective transfer of hydrogen between —NH<sub>2</sub> and —PH<sub>2</sub> functional groups takes place during the cyclic hydrogen storage process, thus the reversibility of hydrogen storage is further improved and the hydrogen desorption energy barrier of the material is reduced.

Short-Range Nanoreaction Effect on the Hydrogen Desorption Behaviors of the MgH2–Ni@C Composite

Doping a catalyst can efficiently improve the hydrogen reaction kinetics of MgH2. However, the hydrogen desorption behaviors are complicated in different MgH2-catalyst systems. Here, a carbon-encapsulated nickel (Ni@C) core-shell catalyst is synthesized to improve the hydrogen storage properties of MgH2. The complicated hydrogen desorption mechanism of the MgH2-Ni@C composite is elucidated. The experimental and theoretical calculation results indicate a short-range nanoreaction effect on the hydrogen desorption behaviors of the MgH2-Ni@C composite. The Ni@C catalysts and the adjacent MgH2 form nanoreaction sites along with preferential hydrogen desorption. The new interface between the in situ formed Mg and residual MgH2 contributes to the subsequent hydrogen desorption. With the nanoreaction sites increased via adding more catalyst, the short-range nanoreaction effect is more prominent; as a comparison, the interface effect becomes weaker or even disappears. In addition, the core-shell structure catalyst shows ultrahigh structural stability and catalytic activity, even after 50 hydrogen absorption and desorption cycles. Hence, this study provides new insights into the complicated hydrogen desorption behaviors and comes up with the short-range nanoreaction effect in the MgH2-catalyst system.

Morphology and microstructure evolution of surface hydride in zirconium alloys during hydrogen desorption process

In the research, we firstly reported the morphology and microstructure evolution of surface hydride in Zircaloy-4-500 ppmH during hydrogen desorption process. The morphological evolution of surface hydride in hydrogen desorption process was investigated with BSE-TOPO and AFM, revealing that the spot-like or string convex features along surface hydride were present at 573 K and disappeared at 1073 K. The microstructure observation with TEM (prepared with cryo-FIB) indicates that the surface region of convex feature actually consists of two layers of fine α-Zr grains, which were the hydrogen-depletion region created by hydrogen release. The formation mechanism of surface hydride convex was the diffusion of hydrogen from the internal to the surface, leading to the generation of multiple δ-hydrides in sub-surface. Therefore, the hydrogen desorption mechanism was also proposed. As the channeling of hydrogen release, surface hydride actually plays a crucial part in hydrogen desorption process.

Thermal desorption spectroscopy studies of hydrogen desorption from rare earth metal trihydrides REH3 (RE=Dy, Ho, Er)

Abstract Rare earth (RE) metals form two stoichiometric hydrides, REH2 and REH3, and for the yttrium group of RE transformation of a FCC (REH2) into an HCP (REH3) lattice takes place during the second step of hydrogenation REH2 + ½ H2 → REH3. Earlier studies of the hydrogen desorption properties of the rare earth hydrides were limited to Y and RE = La, Ce, Pr, Nd, Sm, Gd, Tb and Er. The present work is focused on the studies of the kinetics and mechanism of hydrogen desorption from trihydrides of heavy rare earths, DyH3, HoH3, and ErH3. The Thermal Desorption Spectroscopy (TDS) studies were performed at pressures below 1 × 10−5 mbar during linear heating from room temperature to 1173 K at different heating rates ranging from 1 to 5.5 K/min. Hydrogen desorption traces show the presence of two main events with the low-temperature peak appearing below 573 K, while the second peak is positioned at 1083–1159 K, with the peak temperatures gradually increasing following the rise of the heating rate. Fitting of the peak temperatures in the TDS spectra using the Kissinger method yielded activation energies of hydrogen desorption for both hydrogen desorption events. For DyH3 and ErH3, the shapes of the TDS spectra appear to be well described by a phase-stuctural transformation following a model of nucleation and growth, while for HoH3 the dehydrogenation mechanism includes a phase boundary reaction. This applied model of phase-structural transformations shows differences in dimensionality and rate-limiting steps as related to the studied compound and the desorption events, REH3 → REH2 or REH2 → RE.

New mechanism and improved kinetics of hydrogen absorption and desorption of Mg(In) solid solution alloy milling with CeF3

This paper presents improving the hydrogen absorption and desorption of Mg(In) solid solution alloy through doped with CeF3. A nanocomposite of Mg0.95In0.05-5 wt% CeF3 was prepared by mechanical ball milling. The microstructures were systematically investigated by X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy. And the hydrogen storage properties were evaluated by isothermal hydrogen absorption and desorption, and pressure-composition-isothermal measurements in a temperature range of 230 °C–320 °C. The mechanism of hydrogen absorption and desorption of Mg0.95In0.05 solid solution is changed by the addition of CeF3. Mg0.95In0.05-5 wt% CeF3 nanocomposite transforms to MgH2, MgF2 and intermetallic compounds of MgIn and CeIn3 by hydrogenation. Upon dehydrogenation, MgH2 reacts with the intermetallic compounds of MgIn and CeIn3 forming a pseudo-ternary Mg(In, Ce) solid solution, which is a fully reversible reaction with a reversible hydrogen capacity～4.0 wt%. The symbiotic nanostructured CeIn3 impedes the agglomeration of MgIn compound, thus improving the dispersibility of element In, and finally improving the reversibility of hydrogen absorption and desorption of Mg(In) solution alloy. For Mg0.95In0.05-5 wt% CeF3 nanocomposite, the dehydriding enthalpy is reduced to about 66.1 ± 3.2 kJ⋅mol−1⋅H2, and the apparent activation energy of dehydrogenation is significantly lowered to 71.9 ± 10.0 kJ⋅mol−1⋅H2, a reduction of ～73 kJ⋅mol−1⋅H2 relative to that for Mg0.95In0.05 solid solution. As a result, Mg0.95In0.05-5 wt% CeF3 nanocomposite can release ～57% H2 in 10 min at 260 °C. The improvements of hydrogen absorption and desorption properties are mainly attributed to the reversible phase transition of Mg(In, Ce) solid solution combing with the multiphase nanostructure.

Enhanced low temperature hydrogen desorption properties and mechanism of Mg(BH4)2 composited with 2D MXene

Mg(BH4)2 occupies a large hydrogen storage capacity of 14.7 wt%, and has been widely recognized to be one of the potential candidates for hydrogen storage. In this work, 2D MXene Ti3C2 was introduced into Mg(BH4)2 by a facile ball-milling method in order to improve its dehydrogenation properties. After milling with Ti3C2, Mg(BH4)2–Ti3C2 composites exhibit a novel “layered cake” structure. Mg(BH4)2 with greatly reduced particle sizes are found to disperse uniformly on Ti3C2 layered structure. The initial dehydrogenation temperature of Mg(BH4)2 has been decreased to 124.6 °C with Ti3C2 additive and the hydrogen liberation process can be fully accomplished below 400 °C. Besides, more than 10.8 wt% H2 is able to be liberated from Mg(BH4)2–40Ti3C2 composite at 330 °C within 15 min, while pristine Mg(BH4)2 merely releases 5.3 wt% hydrogen. Moreover, the improved dehydrogenation kinetics can be retained during the subsequent second and third cycles. Detailed investigations reveal that not only Ti3C2 keeps Mg(BH4)2 particles from aggregation during de/rehydrogenation, but also the metallic Ti formed in-situ serves as the active sites to catalyze the decomposition of Mg(BH4)2 by destabilizing the B–H covalent bonds. This synergistic effect of size reduction and catalysis actually contributes to the greatly advanced hydrogen storage characteristics of Mg(BH4)2.

Pd(110)の水素脱離過程解明に向けたチャネリングHERDA装置開発の現状

Pd(110)の水素脱離過程解明に向けたチャネリングHERDA装置開発の現状

Enhanced reversible hydrogen desorption properties and mechanism of Mg(BH4)2-AlH3-LiH composite

The Mg(BH4)2-AlH3-xLiH (x = 0, 0.5, 1) novel ternary composites have been synthesized through mechanical ball milling, their favorable dehydrogenation properties and mechanism have been experimentally investigated. It can be found that during ball milling, a slight amount of Mg(BH4)2 would react with LiH and transform into LiBH4, while most Mg(BH4)2 remained stable after ball milling. Two major dehydrogenation steps can be detected in the Mg(BH4)2-AlH3-xLiH composite, which belong to the decomposition of AlH3 and Mg(BH4)2, respectively. Remarkably, the onset hydrogen desorption temperature of Mg(BH4)2-AlH3-xLiH composite can be reduced to 125.9 °C, with a total hydrogen desorption capacity of 10.3 wt%. It is worth emphasizing that the reversible dehydrogenation capacity is obviously improved to 3.8 wt%, compared to the Mg(BH4)2-AlH3 composite. This reversible capacity can be held for 3 cycles without obvious degeneration. Microstructural analysis on de/rehydrogenated composite has identified the regeneration of [BH4]- in Mg(BH4)2-AlH3-0.5LiH composite and revealed the role of LiH in the cycling hydrogen desorption and absorption processes. The formation of LiBH4 and MgH2 resulted from the rehydrogenation between MgAlB4 and LiH could be helpful for the stability of reversible hydrogen storage performance.

Effect of the hierarchical Co@C nanoflowers on the hydrogen storage properties of MgH2

A hierarchical Co@C nanoflowers are synthesized via a simple route based on a low-temperature solid-phase reaction. The as-prepared hierarchical Co@C nanoflowers have an enhanced catalytic activity on the hydrogen storage properties of MgH2 and thermodynamics and kinetics properties of the MgH2Co@C composite are systematically researched. It is found that the initial desorption temperature of the MgH2Co@C is about 201 °C, 99 °C lower compared to MgH2. And the MgH2Co@C material can release 5.74 wt % within 30 min and 6.08 wt % H2 within 60 min at 300 °C. Whereas, pure as-milled MgH2 only can release 0.37 wt % within 30 min and 1.20 wt % hydrogen within 60 min at the same temperature. Meanwhile, the hydrogen absorption amount of MgH2Co@C achieve 5.96 wt% within 10 min at 300 °C, and the maximum hydrogen absorption amount reach 6.16 wt% within 20 min. In addition, the introduction of hierarchical Co@C nanoflowers also reduces the activation energy (Ea) 46 kJ mol−1, which exhibits a promoted kinetics. In addition, the relative hydrogen desorption mechanism of MgH2Co@C has also been discussed.

Understanding of hydrogen desorption mechanism from defect point of view

Understanding of hydrogen desorption mechanism from defect point of view

Role of chemical interaction between MgH2 and TiO2 additive on the hydrogen storage behavior of MgH2

The present study explores how the additive titania chemically reacts with magnesium hydride and influences the dehydrogenation of MgH2. Quantitative X − ray diffraction study of ball milled MgH2+xTiO2 (x=0.25, 0.33, 0.5 and 1) suggests that Ti substituted MgO is the main reaction product in all the product powders. Convincing evidence is obtained to conclude that Ti dissolution in MgO makes a dramatic behavioral change to MgO; passive MgO turns as an active in-built catalyst. The analysis correlating the dehydrogenation kinetics, composition of in-situ catalyst and sample durability suggests that effectiveness of Ti substituted MgO (MgxTiyOx+y) as a catalyst for MgH2 depends on the concentration of Ti in MgxTiyOx+y rock salt. These observations are immensely helpful for understanding the hydrogen desorption mechanism of metal oxide additives loaded MgH2 system.

Enhanced hydrogen storage performance of MgH2[sbnd]Ni2P/graphene nanosheets

Ni2P/GNS nanocomposite was synthesized by a facile and green hydrothermal technique. Microstructural characterizations demonstrated that Ni2P nanoparticles with an average size of about 5 nm were uniformly distributed in graphene nanosheets. The Ni2P/GNS nanohybrid exhibited enhanced effects on the dehydrogenation properties of MgH2 compared to Ni2P and GNS individually. The onset desorption temperature of MgH2Ni2P/GNS composite reduced by 98 °C in contrast with the pure as-milled MgH2. Moreover, the MgH2Ni2P/GNS composite could release 6.1 wt% H2 (only 0.2 wt% H2 for the pure as-milled MgH2) within 20 min at 325 °C. In addition, the relative hydrogen desorption mechanism of MgH2Ni2P/GNS composite has also been discussed.

マグネシウムハイドライドの水素放出における潜伏期に及ぼす比表面積の影響

Although Mg based hydrogen storage materials absorb hydrogen immediately under appropriate thermodynamic conditions, an obvious incubation period exists for hydrogen desorption. This fact implies that the mechanisms of hydrogen absorption and desorption are different from each other. During hydrogen desorption process, nucleation and growth of Mg are occurring in MgH2. It is considered that free surface is the only nucleation site of Mg in hydrogen desorption process. The nucleation frequency per unit specific surface area should be constant under a fixed temperature and H2 partial pressure. Therefore, it is estimated that the incubation period is proportional to the inverse of specific surface area. The relationship between incubation period and specific surface area of MgH2 was investigated in order to understand the mechanism of incubation period on magnesium-hydrogen system. MgH2 with several kinds of specific surface area were manufactured by changing milling time of a planetary ball mill. A primary Gibbs free energy for dehydrogenation was conducted as −1.94 kJ mol−1 by controlling H2 pressure for measuring incubation period. The results revealed that the incubation period was proportional to the inverse of specific surface area.

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

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

Hydrogen Storage in VNx-Hy Thin Films

Vanadium or its alloy-based hydrides are intensively studied at the moment with regard to their use as hydrogen absorbents. Most experiments were carried out using “bulk” materials. This paper uses ion beam-assisted deposition technology (IBAD) to create thin-film nanocrystalline VNx-Hy hydrogen storages. The transmission electron microscopy and scanning electron microscopy were used to study the initial stages of the film formation. The main mechanisms of the formation of intergranular pores in nanogranular structures have been established. The interrelation of the parameters of the IBAD and those of film structure has been shown. The obtained data allowed for the explanation of the mechanisms of hydrogen absorption and desorption by thin films. It was shown that the availability of branched network of intergranular pores allows VNx-Hy structures to accumulate hydrogen within a few minutes at a pressure of 0.5 MPa. Hydrogen in amount of up to 2.55 wt% is retained in the films of 3 μm thick at room temperature and atmospheric pressure. The hydrogen desorption starts at 100℃.

Controlled mechanochemical synthesis and hydrogen desorption mechanisms of nanostructured Mg2CoH5

Magnesium complex hydrides are attractive for hydrogen storage applications, mainly due to their high volumetric capacities and to their relatively low cost. In this work, nanocrystalline Mg2CoH5 was synthesized with very high yields (97%) by reactive milling cobalt and magnesium under relatively mild processing conditions (30 bar of H2 pressure and 12 h of milling). The behavior of the milled Mg2CoH5 during heating was studied by a combination of several techniques including DSC, QMS, TGA and in-situ synchrotron XRD. It is shown for the first time that two different mechanisms of hydrogen desorption take place. At low temperatures (up to 325 °C), some hydrogen is released by a diffusional mechanism with no change in the crystalline structure of the high temperature γ-Mg2CoH5 phase. At higher temperatures, above 325 °C, the γ-Mg2CoH5 phase becomes unstable and the complex hydride decomposes into Mg, Co and H2. This is the first work to report the diffusional hydrogen desorption mechanism for the Mg2CoH5 or any other complex hydride. Furthermore, a complete description of the allotropic β-Mg2CoH5 to γ-Mg2CoH5 phase transition is provided.

NH3 Mediated or Ion Migration Reaction: The Case Study on Halide–Amide System

Lively debates on hydrogen desorption from the amide-hydride system via either ion migration or NH3 mediated mechanisms have been ongoing since the discovery of the amide-hydride system for hydrogen storage. In this work, we employed kinetic analyses to demonstrate that the mechanism of hydrogen desorption depends on the sample morphology and desorption conditions. Upon the formation of Li amide bromide (Li2NH2Br), the LiNH2 unit is confined in the cage of Br, resulting in less mobility of ion. Hydrogen desorption from the Li2NH2Br-2LiH system appears to follow the NH3 mediated mechanism even if the two starting chemicals have been intensively ball milled. On the other hand, the migrations of Li+ and H+ play important roles leading to H-2 formation from the direct combination of H+ (from -NH2) and H- (from LiH) when LiNH2 and LiH are intimately in contact.