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HighlightsA comprehensive discussion of the recent advances in the nanostructure engineering of Mg-based hydrogen storage materials is presented.The fundamental theories of hydrogen storage in nanostructured Mg-based hydrogen storage materials and their practical applications are reviewed.The challenges and recommendations of current nanostructured hydrogen storage materials are pointed out.With the depletion of fossil fuels and global warming, there is an urgent demand to seek green, low-cost, and high-efficiency energy resources. Hydrogen has been considered as a potential candidate to replace fossil fuels, due to its high gravimetric energy density (142 MJ kg−1), high abundance (H2O), and environmental-friendliness. However, due to its low volume density, effective and safe hydrogen storage techniques are now becoming the bottleneck for the \"hydrogen economy\". Under such a circumstance, Mg-based hydrogen storage materials garnered tremendous interests due to their high hydrogen storage capacity (~ 7.6 wt% for MgH2), low cost, and excellent reversibility. However, the high thermodynamic stability (ΔH =  − 74.7 kJ mol−1 H2) and sluggish kinetics result in a relatively high desorption temperature (> 300 °C), which severely restricts widespread applications of MgH2. Nano-structuring has been proven to be an effective strategy that can simultaneously enhance the ab/de-sorption thermodynamic and kinetic properties of MgH2, possibly meeting the demand for rapid hydrogen desorption, economic viability, and effective thermal management in practical applications. Herein, the fundamental theories, recent advances, and practical applications of the nanostructured Mg-based hydrogen storage materials are discussed. The synthetic strategies are classified into four categories: free-standing nano-sized Mg/MgH2 through electrochemical/vapor-transport/ultrasonic methods, nanostructured Mg-based composites via mechanical milling methods, construction of core-shell nano-structured Mg-based composites by chemical reduction approaches, and multi-dimensional nano-sized Mg-based heterostructure by nanoconfinement strategy. Through applying these strategies, near room temperature ab/de-sorption (< 100 °C) with considerable high capacity (> 6 wt%) has been achieved in nano Mg/MgH2 systems. Some perspectives on the future research and development of nanostructured hydrogen storage materials are also provided.

Underground hydrogen storage is a long‐duration energy storage option for a low‐carbon economy. Although research into the technical feasibility of underground hydrogen storage is ongoing, existing underground gas storage (UGS) facilities are appealing candidates for the technology because of their ability to store and deliver natural gas. We estimate that UGS facilities in the United States (U.S.) can store 327 TWh (9.8 MMT) of pure hydrogen. A complete transition to hydrogen storage would reduce the collective working‐gas energy of UGS facilities by ∼75%; however, most (73.2%) UGS facilities could maintain current energy demand using a 20% hydrogen‐natural gas blend. U.S. UGS facilities can buffer 23.9%–44.6% of the high and low hydrogen demand projected for 2050, respectively, which exceeds the current percentage of natural gas demand buffered by storage. Thus, transitioning UGS infrastructure to hydrogen could substantially reduce the number of new hydrogen storage facilities needed to support a hydrogen economy. Plain Language Summary Hydrogen is a high energy content fuel that can be produced with low or zero greenhouse gas emissions from water and other chemicals. Creating hydrogen during periods of energy surplus and storing it underground is one long‐duration, low‐emission, energy storage option that can balance supply and demand for an entire electric grid. In the United States (U.S.), existing underground gas storage (UGS) facilities are a logical first place to consider subsurface hydrogen storage, because their geology has proven favorable for storing natural gas. We estimated that existing UGS facilities can store 327 TW‐h (9.8 million metric tons) of pure hydrogen. Transitioning from natural gas to pure hydrogen storage would reduce the total energy stored in existing UGS facilities by ∼75%. Storing hydrogen‐natural gas mixtures also reduces energy storage potential, but most (73.2%) UGS facilities can meet current energy demands with a 20% hydrogen blend. U.S. UGS facilities can store 23.9%–44.6% of the projected high and low hydrogen demand for 2050, respectively, suggesting that a partial transition of UGS infrastructure could reduce the need for new hydrogen storage facilities. These findings motivate research that explores the technical feasibility of underground hydrogen storage in natural gas storage reservoirs. Key Points The total hydrogen working‐gas energy of underground gas storage facilities in the United States is estimated to be 327 TW‐hours Most (73.2%) underground gas storage facilities can store hydrogen blends up to 20% and continue to meet their current energy demand Hydrogen storage in existing underground gas storage facilities can sufficiently buffer the hydrogen demand projected for 2050

Numerous reviews on hydrogen storage have previously been published. However, most of these reviews deal either exclusively with storage materials or the global hydrogen economy. This paper presents a review of hydrogen storage systems that are relevant for mobility applications. The ideal storage medium should allow high volumetric and gravimetric energy densities, quick uptake and release of fuel, operation at room temperatures and atmospheric pressure, safe use, and balanced cost-effectiveness. All current hydrogen storage technologies have significant drawbacks, including complex thermal management systems, boil-off, poor efficiency, expensive catalysts, stability issues, slow response rates, high operating pressures, low energy densities, and risks of violent and uncontrolled spontaneous reactions. While not perfect, the current leading industry standard of compressed hydrogen offers a functional solution and demonstrates a storage option for mobility compared to other technologies.

Few hydrogen adsorbents balance high usable volumetric and gravimetric capacities. Although metal-organic frameworks (MOFs) have recently demonstrated progress in closing this gap, the large number of MOFs has hindered the identification of optimal materials. Here, a systematic assessment of published databases of real and hypothetical MOFs is presented. Nearly 500,000 compounds were screened computationally, and the most promising were assessed experimentally. Three MOFs with capacities surpassing that of IRMOF-20, the record-holder for balanced hydrogen capacity, are demonstrated: SNU-70, UMCM-9, and PCN-610/NU-100. Analysis of trends reveals the existence of a volumetric ceiling at ∼40 g H 2  L −1 . Surpassing this ceiling is proposed as a new capacity target for hydrogen adsorbents. Counter to earlier studies of total hydrogen uptake in MOFs, usable capacities in the highest-capacity materials are negatively correlated with density and volumetric surface area. Instead, capacity is maximized by increasing gravimetric surface area and porosity. This suggests that property/performance trends for total capacities may not translate to usable capacities. Considering the large number of existing synthesised and hypothesised metal-organic frameworks, determining which materials perform best for given applications remains a challenge. Here, the authors screen the usable hydrogen uptake capacities of nearly 500,000 MOFs, and find that three frameworks outperform the current record-holder.

In the process of building a new power system with new energy sources as the mainstay, wind power and photovoltaic energy enter the multiplication stage with randomness and uncertainty, and the foundation and support role of large-scale long-time energy storage is highlighted. Considering the advantages of hydrogen energy storage in large-scale, cross-seasonal and cross-regional aspects, the necessity, feasibility and economy of hydrogen energy participation in long-time energy storage under the new power system are discussed. Firstly, power supply and demand production simulations were carried out based on the characteristics of new energy generation in China. When the penetration of new energy sources in the new power system reaches 45%, long-term energy storage becomes an essential regulation tool. Secondly, by comparing the storage duration, storage scale and application scenarios of various energy storage technologies, it was determined that hydrogen storage is the most preferable choice to participate in large-scale and long-term energy storage. Three long-time hydrogen storage methods are screened out from numerous hydrogen storage technologies, including salt-cavern hydrogen storage, natural gas blending and solid-state hydrogen storage. Finally, by analyzing the development status and economy of the above three types of hydrogen storage technologies, and based on the geographical characteristics and resource endowment of China, it is pointed out that China will form a hydrogen storage system of “solid state hydrogen storage above ground and salt cavern storage underground” in the future.

High hydrogen absorption and desorption rates are two significant index parameters for the applications of hydrogen storage tanks. The analysis of the hydrogen absorption and desorption behavior using the isothermal kinetic models is an efficient way to investigate the kinetic mechanism. Multitudinous kinetic models have been developed to describe the kinetic process. However, these kinetic models were deduced based on some assumptions and only appropriate for specific kinetic measurement methods and rate-controlling steps (RCSs), which sometimes lead to confusion during application. The kinetic analysis procedures using these kinetic models, as well as the key kinetic parameters, are unclear for many researchers who are unfamiliar with this field. These problems will prevent the kinetic models and their analysis methods from revealing the kinetic mechanism of hydrogen storage alloys. Thus, this review mainly focuses on the summarization of kinetic models based on different kinetic measurement methods and RCSs for the chemisorption, surface penetration, diffusion of hydrogen, nucleation and growth, and chemical reaction processes. The analysis procedures of kinetic experimental data are expounded, as well as the effects of temperature, hydrogen pressure, and particle radius. The applications of the kinetic models for different hydrogen storage alloys are also introduced.

Porous carbons have been extensively investigated for hydrogen storage but, to date, appear to have an upper limit to their storage capacity. Here, in an effort to circumvent this upper limit, we explore the potential of oxygen-rich activated carbons. We describe cellulose acetate-derived carbons that combine high surface area (3800 m 2  g −1 ) and pore volume (1.8 cm 3  g −1 ) that arise almost entirely (>90%) from micropores, with an oxygen-rich nature. The carbons exhibit enhanced gravimetric hydrogen uptake (8.1 wt% total and 7.0 wt% excess) at −196 °C and 20 bar, rising to a total uptake of 8.9 wt% at 30 bar, and exceptional volumetric uptake of 44 g l −1 at 20 bar, and 48 g l −1 at 30 bar. At room temperature they store up to 0.8 wt% (excess) and 1.2 wt% (total) hydrogen at only 30 bar, and their isosteric heat of hydrogen adsorption is above 10 kJ mol −1 . Hydrogen is attractive as a clean fuel for motor vehicles and porous carbons represent promising hydrogen storage materials. Here, Mokaya and colleagues incorporate oxygen-rich functional groups into porous carbons with high microporosity, showing that such materials exhibit significantly enhanced H 2 storage capacity.

High‐entropy alloys (HEAs) have emerged as a groundbreaking class of materials poised to revolutionize solid‐state hydrogen storage technology. This comprehensive review delves into the intricate interplay between the unique compositional and structural attributes of HEAs and their remarkable hydrogen storage performance. By meticulously exploring the design strategies and synthesis techniques, encompassing experimental procedures, thermodynamic calculations, and machine learning approaches, this work illuminates the vast potential of HEAs in surmounting the challenges faced by conventional hydrogen storage materials. The review underscores the pivotal role of HEAs' diverse elemental landscape and phase dynamics in tailoring their hydrogen storage properties. It elucidates the complex mechanisms governing hydrogen absorption, diffusion, and desorption within these novel alloys, offering insights into enhancing their reversibility, cycling stability, and safety characteristics. Moreover, it highlights the transformative impact of advanced characterization techniques and computational modeling in unraveling the structure–property relationships and guiding the rational design of high‐performance HEAs for hydrogen storage applications. By bridging the gap between fundamental science and practical implementation, this review sets the stage for the development of next‐generation solid‐state hydrogen storage solutions. It identifies key research directions and strategies to accelerate the deployment of HEAs in hydrogen storage systems, including the optimization of synthesis routes, the integration of multiscale characterization, and the harnessing of data‐driven approaches. Ultimately, this comprehensive analysis serves as a roadmap for the scientific community, paving the way for the widespread adoption of HEAs as a disruptive technology in the pursuit of sustainable and efficient hydrogen storage for a clean energy future. High‐entropy alloys (HEAs) revolutionize solid‐state hydrogen storage through their unique compositional and structural characteristics. This review explores the interplay between design strategies and synthesis techniques shaping HEAs' hydrogen storage properties. From CALPHAD predictions to first‐principles calculations and from thermal methods to cold forming, innovative approaches unlock HEAs' potential as next‐generation materials for efficient and sustainable hydrogen storage solutions.

Supplying hydrogen to industrial users is now a major business around the world. One of the problems, before hydrogen can be implemented into today’s infrastructure is storing the hydrogen. In this report, we introduced a high-pressure milling method for preparing the MgH 2 catalyzed with Ni nanoparticle. We have reactively milled the MgH 2 + 2 mol % Ni, which has size ∼90 nm, under 100 bar of hydrogen. The structural changes during milling were characterized by XRD and high-resolution scanning electron microscopy. The hydrogen sorption properties were studied by gravimetric analysis. As the results, it was showed that the milling process reduced into 2 h. The sorption kinetics was proceeding 5.3 wt% of hydrogen around 5 min at 300°C, while desorption in 50 mbar was completed within 4 min. Preparing the Mg-based hydrides under high pressure with 2 mol% Ni in nanoscale as catalyst improved the hydrogen storage properties and decreased the milling time, as well.

HighlightsA MgH2/TiO2 heterostructure with nano MgH2 assembled on oxygen vacancy-rich 2D TiO2 nanosheets was successfully fabricated via a simple solvothermal strategy.The MgH2/TiO2 heterostructure shows rapid desorption kinetics, low dehydrogenation temperature, and excellent cycling stability.In situ HRTEM observations and ex situ XPS analyses reveal that multi-valance of Ti species, presence of abundant oxygen vacancies, formation of catalytic Mg-Ti oxides, and confinement of TiO2 nanosheets, contribute to the high stability and kinetically accelerated hydrogen sorption performances of Mg.MgH2 has attracted intensive interests as one of the most promising hydrogen storage materials. Nevertheless, the high desorption temperature, sluggish kinetics, and rapid capacity decay hamper its commercial application. Herein, 2D TiO2 nanosheets with abundant oxygen vacancies are used to fabricate a flower-like MgH2/TiO2 heterostructure with enhanced hydrogen storage performances. Particularly, the onset hydrogen desorption temperature of the MgH2/TiO2 heterostructure is lowered down to 180 °C (295 °C for blank MgH2). The initial desorption rate of MgH2/TiO2 reaches 2.116 wt% min−1 at 300 °C, 35 times of the blank MgH2 under the same conditions. Moreover, the capacity retention is as high as 98.5% after 100 cycles at 300 °C, remarkably higher than those of the previously reported MgH2-TiO2 composites. Both in situ HRTEM observations and ex situ XPS analyses confirm that the synergistic effects from multi-valance of Ti species, accelerated electron transportation caused by oxygen vacancies, formation of catalytic Mg-Ti oxides, and stabilized MgH2 NPs confined by TiO2 nanosheets contribute to the high stability and kinetically accelerated hydrogen storage performances of the composite. The strategy of using 2D substrates with abundant defects to support nano-sized energy storage materials to build heterostructure is therefore promising for the design of high-performance energy materials.