Enhanced Hydrogen Adsorption on Hydrochloric Acid–Activated Cu–BDC Metal Organic Framework: Structural and Performance Analysis

Hydrogen adsorption performance of Cu-BTC/graphene aerogel composite: A combined experimental and computational study

Improved synthesis and hydrogen storage of a microporous metal–organic framework material

Hydrogen is a flexible energy carrier with the potential to replace fossil fuels as a clean and renewable energy source. However, efficient storage systems under ambient conditions are essential for practical applications. This study investigates magnesium–nickel-based metal hydrides for hydrogen storage, enhanced with 20% graphite or additional nickel. The synthesized samples—MgNi2, MgNi2 + graphite 20%, Mg2Ni + graphite 20%, and Mg2Ni + Ni 1:1—were characterized using XRD, BET, SEM-EDX, and hydrogen temperature-programmed desorption (TPD). Crystallite sizes were found to be 132.125, 137.125, 77.168, and 92.335 nm, respectively. BET analysis revealed surface areas of 2.144, 1.664, 7.113, and 2.308 m2/g, corresponding pore volumes of 0.0038, 0.0031, 0.0137, and 0.0100 cm3/g. TPD results showed that Mg2Ni + graphite 20% had the fastest desorption rate (46 min), consistent with its highest surface area and pore volume. This sample also achieved the highest hydrogen adsorption capacity at 0.0615 mmol/g. These findings demonstrate that Mg-Ni hydrides, especially those modified with graphite, offer promising performance for hydrogen storage applications, particularly in systems requiring rapid desorption and efficient kinetics, such as fuel-cell electric vehicles. The results highlight the potential of tailored Mg-Ni composites for advanced hydrogen storage solutions.

Limited conventional energy resources and serious environmental calamities have motivated researchers to find new and efficient sources of energy. The considerable efforts devoted to this end include the development of bio-diesel, solar cells, coal liq-uefaction/gasification technologies, and fuel cells. Hydrogen is considered by many an ideal energy source owing to its renewable and clean energy characteristics. In addition, it mostly produces water, which is eco-friendly compared to the byproducts of many other energy sources [1-6]. To use hydrogen as an energy source, various hydrogen stor -age methods such as the use of metal hydrides, liquefied hydrogen, and adsorption of hydrogen in porous materials have been studied [7-14]. The adsorption of hydrogen in porous materials is particularly suitable for hydrogen storage, which is critical for suit -ably utilizing hydrogen energy, owing to the reversibility and stability of this method. To date, the wide ranging attempts to develop hydrogen storage mechanisms include studies on carbon materials [15-17], metal-organic frameworks, and zeolites [18-21]. Carbon materials offer many advantages for hydrogen storage, such as easy preparation, suitable surface functional groups, low mass density, thermal stability, and hydropho -bicity [22-24]. Carbon aerogels (CAs) in particular have been recognized as potential hydrogen storage materials because of their suitable structural properties, controllable mass densities, high specific surface areas, and mesopore volumes. However, it is neces -sary to modify the surfaces of carbon materials in order to reach the hydrogen storage capacities determined by the US Department of Energy (DOE).Carbon materials containing transition metals such as platinum, copper, vanadium, and nickel exhibit attractive hydrogen storage properties [10,22,25]. Nickel is particularly prom -ising since it is easily obtained on Earth, and it is inexpensive compared to other metals and enhances hydrogen storage properties. Improved hydrogen storage capacities have been obtained with nickel-plated porous carbon nanofibers owing to the spillover of hydrogen molecules onto the metal-carbon interfaces. In general, the presence of nickel particles on carbon materials has been shown to enhance the hydrogen storage capacity [3,9,19].In this work, CAs were chemically activated by KOH to produce well-developed pore structures and ultimately increase the hydrogen storage capacities. Nickel-loaded activated carbon aerogels (ACAs/Ni hybrid materials) with various nickel content were prepared. Ni particles were loaded onto ACAs to introduce hydrogen-favorable active sites onto the ACA surfaces and improve the hydrogen storage capacities.The CAs were prepared using resorcinol as the carbon precursor and formaldehyde as the initiator. Resorcinol (7.5 g) was dissolved in a solution of distilled water (75 mL) and formaldehyde (25 g). Sodium carbonate was then added to this solution, and the mixture was stirred for 3 h in an open container and dried for 3 h at room temperature. Subsequently, the wet gel was dried at 80°C for 48 h and then immersed in an acetone solution for 24 h without stirring. The aerogels were obtained after drying at 80°C for 24 h. Prior to use, the aerogels were carbonized in a furnace with a heating rate of 2°Cmin

High quality multi-walled carbon nanotubes and single-walled carbon nanotubes are synthesized and purified with small amount of metal catalyst impurities remaining. The activation of CNTs by air or CO2 is effective to open the tube ends, remove the amorphous carbon and create more defects thus improving hydrogen adsorption. However, the CNTs can only adsorb less than 1 wt% of hydrogen at cryogenic temperature and atmospheric pressure confirming that CNTs are not promising media for hydrogen storage. Activated carbon fibers (ACFs) show high hydrogen adsorption capacity due to their highly developed microporosity. It is found that high oxidation temperatures and strong mechanical ball milling have a detrimental effect on the enhancement of the surface area and micropore (<2 nm) volume of the treated ACFs samples. Comparison of the pore size distribution and hydrogen adsorption isotherms of ACFs indicates that pores of about 0.57 nm width start adsorbing hydrogen at 77 K at a minimum pressure of approximately 3-4 mmHg and pores of 0.75 nm start adsorbing H2 at 77 K at a pressure of 9-10 mmHg. The ultramicropores (< 0.7 nm) of the ACF samples dominate the hydrogen adsorption at room temperature. The ultramicropores represent the higher energy adsorption sites that can adsorb gas molecules at high temperature or very low pressure. However, hydrogen molecules are not only trapped in the ultramicropores, but also adsorbed in the supermicropores (0.7-2 nm) at 77 K. From our experimental and modeling studies, the hydrogen adsorption on the carbon surface follows monolayer mechanism. The Langmuir model is only partly successful in fitting the experimental isotherms due to the supercritical adsorption nature under the tested conditions. Nevertheless, supercritical adsorption model successfully fits the experimental hydrogen excess adsorption on ACFs and evaluates absolute adsorption and total storage capacity on the ACF materials. The evaluated total hydrogen storage capacity on raw ACFs achieves 5.9 wt% closes to DOE 2010 gravimetric target for hydrogen storage. Hydrogen adsorption on ball milled metal-carbon composites also follows physisorption mechanism. However, reduced Ni/NaY composites exhibit enhanced hydrogen adsorption compared with calcined Ni/NaY composites in air. The introduction of nickel results in reduction of hydrogen physisorption due to decreased micropore volume and surface area. Nevertheless, dissociative hydrogen adsorption and subsequent hydrogen spillover at high pressure have improved hydrogen adsorption capacity by a factor of 0.4 and 0.86 on reduced 10% NiNaY composite 77 and 303 K, respectively.

Ball milling and compression effects on hydrogen adsorption by MOF:Pt/carbon mixtures

The existing obstacles toward the usage of fossil fuels as the prime mover of the cars have improved the commercialization of the fuel cells and batteries to replace the internal combustion engines (ICEs). Although the required infrastructure is already established for the ICE cars, the low number of hydrogen refueling stations, low range of batteries, high charging time of the batteries, and the size/weight of the hydrogen tanks are the main concerns toward the transition from ICE cars to environmentally friendly alternatives.Fuel cells can be directly used in the vehicles as the prime mover (mobility applications), or they can be considered as the energy provider of the electric vehicle charging stations (stationary applications). Although the hydrogen storage is not being considered as an obstacle for the stationary applications, the required weight and size of the hydrogen tanks is a barrier to facilitate the usage of hydrogen in the automotive sector. Based on the given standards [1], it is possible to pressurize hydrogen up to 700 bars, hence reducing the size of the hydrogen tanks. This solution has been already used in the development of the Toyota Mirai, which has 114kW/155hp power and 500km range with the fuel consumption of 0.76 kg H2/100km [2]. Similarly, Honda Clarity could reach the range of 650km with 5kg of hydrogen tank capacity at the rated power of 130kW/ 176hp [3]. Although pressurizing the hydrogen is a feasible solution, it will demand further costs and safety procedures to reach the 700 bars. In other words, the best solution would be reaching the same driving range without pressurizing the hydrogen.In this regard, Metal-Organic Framework (MOF) can be used to increase the hydrogen adsorption in the hydrogen tank due to higher gravimetric storage density. Among different types of MOFs, the MOF-5 has shown promising results to increase the hydrogen storage up to wt. 10% absolute at 70 bar and 77K. It is believed that the low thermal conductivity of the MOF-5 can reduce the performance of the system when rapid gas uptake and release is required [4]. Although there have been studies to evaluate the overall possibilities of using MOF-5 to improve the adsorption of hydrogen in the hydrogen tanks, there is not a comprehensive study to simulate and characterize the changes in the hydrogen adsorption once the hydrogen tanks are filled with different types of MOFs.The goal of this study is to use the computational fluid dynamic methodologies to model a hydrogen tank filled with MOFs and to analyze the hydrogen adsorption by the changes in the time. This study can a step toward improving the design of the hydrogen tanks, which will facilitate the hydrogen storage at low pressures close to the ambient temperatures. This study can be also a good start to find the right type of MOF to be used in the hydrogen tanks to have the highest possible hydrogen adsorption. The developed model is based on mass, momentum, and energy conservation equations of the adsorbent-adsorbate system composed of gaseous and adsorbed hydrogen, adsorbent bed and tank wall. It is noteworthy to mention that the adsorption process is based on the modified Dubinin-Astakov (D-A) adsorption isotherm model. Keywords : Hydrogen Storage; Metal Organic Frameworks; Adsorption; Fuel cells. Figure 1

The mechanical stability of activated ZIF-templated carbon materials, prepared via liquid impregnation and chemical vapour deposition (CVD) methods, was investigated by compaction at various pressures (compaction loads of 5 and 10 tonnes equivalent to 370 and 740 MPa, respectively). Compaction at 5 tonnes (370 MPa) was, unusually, found to increase the textural properties (surface area and pore volume) and gas (hydrogen and CO2) uptake capacity. In particular, compaction at 5 tonnes resulted in higher micropore surface area and pore volume, and an overall rise in the total surface area and pore volume. Compaction resulted in an improved gas uptake capacity of 6.5 wt% hydrogen (at −196 °C and 20 bar) and 2.4 mmol g−1 of CO2 (at 25 °C and 1 bar) for an activated ZIF-templated carbon compacted at 5 tonnes following preparation via liquid impregnation and carbonisation at 900 °C. When the carbon was compacted at 10 tonnes (740 MPa), the hydrogen and CO2 uptake was marginally lower at 5.7 wt% and 2.2 mmol g−1, respectively, compared to the uptake of 6.2 wt% hydrogen and 2.0 mmol g−1 CO2 for the equivalent non-compacted sample. More importantly, increase in packing density after compaction resulted in up to 70% improvement in volumetric hydrogen uptake, which reached 42.3 g l−1 at −196 °C and 20 bar, much higher than that for conventional activated carbons, and one of the highest values ever reported under these conditions. The genesis of the increase in textural properties after compaction appears to be linked to the pore size distribution and mechanical stability of the activated ZIF-templated carbons and their structural rearrangement under compaction, especially at a load of 5 tonnes that results in an increase in the proportion of microporosity.

Machine learning assisted predictions for hydrogen storage in metal-organic frameworks

Room-temperature hydrogen storage performance of metal-organic framework/graphene oxide composites by molecular simulations

Hydrogen is a promising candidate for renewable energy storage and transportation due to its high energy density and zero carbon emissions. Its practical applications face challenges related to safe, efficient storage and release systems. This review article investigates advanced nanostructured materials for hydrogen storage, including metal acetylide and cyanide complexes, B,N-doped γ-graphyne nanotubes (γ-GNT), lithium-phosphide double helices, and Ni-decorated carbon-based clusters. Density Functional Theory (DFT) based computations are used to analyze binding energies, thermodynamic stability, and adsorption mechanisms. Ni-decorated C12N12 nanoclusters demonstrate enhanced storage capacities, binding up to eight H2 molecules with a favorable N-(μ-Ni)-N configuration. Lithium-phosphide double helices show potential for 9.6 wt% hydrogen storage within a stable, semiconducting framework. Functionalization of γ-GNT with OLi2 at boron-doped sites significantly enhances storage potential, achieving optimal hydrogen binding energies for practical applications. Additionally, metal acetylide and cyanide complexes, stabilized by noble gas insertion, display thermodynamically favorable hydrogen adsorption. These results highlight the potential of these functionalized nanostructures for achieving high-capacity, reversible hydrogen storage. The nanostructures in this study, such as γ-graphyne nanotubes (γ-GNT), lithium-phosphide double helices, metal acetylide and cyanide complexes, and Ni-decorated carbon-based clusters, are selected based on their ability to exhibit complementary hydrogen adsorption mechanisms, including physisorption and chemisorption. γ-GNT offers high surface area and tunable electronic properties, ideal for physisorption enhanced by heteroatom doping. Lithium-phosphide double helices facilitate Kubas-like chemisorption through unsaturated lithium centers. Metal acetylide and cyanide complexes stabilize hydrogen adsorption via charge transfer and conjugated frameworks, while Ni-decorated clusters combine polarization-induced physisorption. These materials represent a strategic approach to addressing the challenges of hydrogen storage through diverse and synergistic mechanisms. The review also addresses challenges and outlines future directions to advance hydrogen's role as a sustainable fuel.

Synergistic effect of hydrogen spillover and nano-confined AlH3 on room temperature hydrogen storage in MOFs: By GCMC, DFT and experiments

The role of transition metal doping in enhancing hydrogen storage capacity in porous carbon materials

The volumetric hydrogen capacity remains one of the most challenging criteria for on-board hydrogen storage system requirements. Here a new concept for hydrogen storage of porous aromatic frameworks (PAFs) impregnated with lithium-decorated fullerenes (Li6C60) is described. The loading of Li6C60 and the effect on the adsorption of hydrogen (H2) has been investigated by molecular simulation. It is shown that the incorporation of Li6C60 can enhance the volumetric capacity of H2 from 12 to 44 g L(-1), a 260% increase at 10 bar and 77 K. The impregnation of Li6C60 increases the heat of adsorption and surface area at the cost of the available pore volume. However, the increase in adsorbed hydrogen outweighs any pore volume loss under optimized Li6C60 loading and operating conditions. In addition, the H2 volumetric uptake is shown to correlate with the volumetric surface area at all pressures whereas the H2 gravimetric uptake correlates with the heat of adsorption at low pressures, surface area at moderate pressures, and pore volume at high pressures.

Hydrogen can act as a potential alternative to fossil fuels; however, storage of this energy source is a challenge to overcome. Researchers have been concentrating on geological hydrogen storage in sandstones and shales. Gas in the latter porous rock is primarily stored in the adsorbed phase, to which inorganic minerals, like montmorillonite, illite, and kaolinite, contribute significantly. In this work, the adsorption of gaseous hydrogen on different clay and clay minerals has been studied experimentally at low-pressure–low-temperature (LPLT, 77 K) and high-pressure–high-temperature (HPHT, 313 K) conditions. Further, the pore characteristics of the selected clay samples have been analyzed using low-pressure N2 (77 K) and CO2 (273 K) adsorption. Scanning electron microscopy (SEM) images of the samples have been utilized to study their morphology, particle sizes, and pore structures. The role of pore structure parameters on hydrogen adsorption at LPLT and HPHT has been investigated. Through these investigations, it has been found that the specific surface area and micropore volume positively affect hydrogen adsorption and the average pore width affects it negatively. Further, the applicability of some well-known adsorption models, like Langmuir, Freundlich, Toth, and Sips, has been investigated. It has been found that the Langmuir model gives a poor fit in both experimental conditions. The Toth and Sips models are good at LPLT as well as HPHT conditions.