Metal-organic frameworks-based hydrogen storage strategies and applications

Fine-tuned MOF-74 type variants with open metal sites for high volumetric hydrogen storage at near-ambient temperature

Energy is regarded as a key resource that may encourage numerous companies to expand and flourish given the rapid advancement of technology. However, due to the contamination of the usage of traditional fossil fuels, deploying new and clean energy resources is the concentrated solution. New energy sources such as wind energy and solar energy are constantly being developed. In addition, three methods exist for storing hydrogen that is a typical clean energy source, including compressed gas storage, cryogenic liquid gas storage, and hydrogen storage materials via adsorption and desorption. As a result, hydrogen storage is receiving more and more attention, and different hydrogen storage materials have been developed. This research will introduce the application of four different types of porous materials in the field of hydrogen storage, including zeolites, activated carbons (AC), carbon nanotubes (CNTs), and metal-organic frameworks (MOFs). Hydrogen can be successfully adsorbed on these materials to varying degrees through chemisorption and physisorption. For improving the hydrogen storage capability (HSC), synthetic strategies such as doping metal elements and synthesizing composite porous materials were designed and used to enhance the hydrogen storage properties of the materials. In the future, satisfying the U.S. Department of Energy (DOE) target would stimulate more and more great-performing porous materials to be synthesized, which can provide a new idea for new hydrogen storage technologies.

Recent advances and remaining challenges of nanostructured materials for hydrogen storage applications

Hydrogen is a clean and high-energy fuel, yet its safe and efficient storage remains a key obstacle to widespread adoption. Metal-organic frameworks (MOFs), with their high surface area and tunable porosity, have emerged as promising candidates for solid-state hydrogen storage. In this work, we introduce a graph-based machine learning framework for predicting hydrogen uptake in MOFs by integrating spectral graph theory with data-driven modeling. Molecular structures are represented as weighted graphs from which we extract 20 graph-based descriptors─including Laplacian spectral features, degree statistics, and Zagreb indices─that capture both topological and geometric characteristics of the framework. These interpretable descriptors are used to train multiple regression models on a data set of 3300 MOFs from the Cambridge Structural Database. The XGBoost regressor achieved the highest performance in predicting hydrogen uptake, with a coefficient of determination (R2) of 0.737, RMSE of 0.850% wt, and MAE of 0.433% wt for gravimetric uptake (UG); and a coefficient of determination (R2) of 0.698, RMSE of 4.467 g H2/L, and MAE of 3.045 g H2/L for volumetric uptake (UV). Beyond accurate prediction, the framework enables inverse materials design by identifying graph-based motifs that contribute to improved storage capacity. This integration of chemical graph theory with machine learning provides a scalable, interpretable, and computationally efficient pathway for the discovery of next-generation MOFs tailored for hydrogen storage and other clean energy applications.

Recent advances in metastable alloys for hydrogen storage: a review

In petroleum refining industries, the fracturing process allows for the cracking of long-chain hydrocarbons into a mixture of small olefin and paraffin molecules that are then separated via the energetically and monetarily demanding cryogenic distillation process. In an attempt to mitigate both energetic and capital consumptions, selective sorption of light hydrocarbons by tunable sorbents, such as metal-organic frameworks (MOFs), appears to be the most promising alternative for a more efficient gas separation process. MOFs are novel porous materials assembled from inorganic bricks connected by organic linkers. From a crystal engineering stand point, MOFs are advantageous in creating a range of microporous (0.2–2.0 nm) to mesoporous (>50 nm) void cavities, presenting unique opportunities for the functionalization of both the organic linkers and the void. Of significant importance is the MOF-74-M family (M = metal), characterized by a high density of open metal sites, that is not fully coordinated metal centers. This family of MOF is also known as CPO-27-M. MOF-74 have demonstrated more separation potential than other known MOFs and zeolites. Density functional theory (DFT), as implemented within a linear combination of atomic orbital (LCAO) approach, has been used to investigate the selective sorption of C1-C4hydrocarbons in MOF-74-Mg/Zn. The study was first implemented by adopting a molecular cluster approach, and later by applying periodic boundary conditions (PBC). While both modellistic approaches agree in showing significant differences in binding energies between olefins and paraffins adsorbed at the MOFs’ open metal sites, results reported at the molecular cluster level show underestimation when compared to those obtained at the PBC level. The use of PBC models allow for the correcting of binding energies for basis set superposition error (BSSE), molecular lateral interaction (LI), zero-point energy (ZPE), and thermal energy (TE) contributions. As such, results obtained at the PBC level are directly comparable to experimental calorimetric values (i.e., heat of adsorptions). This work discusses, for the first time, the origin of the fictitious agreement between binding energies obtained with molecular clusters and experimental heats of adsorption, identifying its origin as due to compensation of errors. Spectroscopy studies based on the intensities and frequency shifts with respect to the molecules in the gas phase are presented as a further investigation of the interaction of the small hydrocarbons (C1-C2) with the open metal sites in MOF-74-Mg. In an attempt to provide a more comprehensive description of the behavior of the hydrocarbon molecules, results from diffusion mechanism studies

Two open metal sites on the same metal: Dynamics of CO2 in MOF UTSA-74

Conventional storage of large amounts of hydrogen in its molecular form is difficult and expensive because it requires employing either extremely high pressure gas or very low temperature liquid. Because of the importance of hydrogen as a fuel, the DOE has set system targets for hydrogen storage of gravimetric (5.5 wt%) and volumetric (40 g L-1) densities to be achieved by 2015. Given that these are system goals, a practical material will need to have higher capacity when the weight of the tank and associated cooling or regeneration system is considered. The size and weight of these components will vary substantially depending on whether the material operates by a chemisorption or physisorption mechanism. In the latter case, metal-organic frameworks (MOFs) have recently been identified as promising adsorbents for hydrogen storage, although little data is available for their sorption behavior. This grant was focused on the study of MOFs with these specific objectives. (1) To examine the effects of functionalization, catenation, and variation of the metal oxide and organic linkers on the low-pressure hydrogen adsorption properties of MOFs. (2) To develop a strategy for producing MOFs with high surface area and porosity to reduce the dead space and increase the hydrogen storage capacity per unit volume. (3) To functionalize MOFs by post synthetic functionalization with metals to improve the adsorption enthalpy of hydrogen for the room temperature hydrogen storage. This effort demonstrated the importance of open metal sites to improve the adsorption enthalpy by the systematic study, and this is also the origin of the new strategy, which termed isoreticular functionalization and metalation. However, a large pore volume is still a prerequisite feature. Based on our principle to design highly porous MOFs, guest-free MOFs with ultrahigh porosity have been experimentally synthesized. MOF-210, whose BET surface area is 6240 m2 g-1 (the highest among porous solids), takes up 15 wt% of total H2 uptake at 80 bar and 77 K. More importantly, the total H2 uptake by MOF-210 was 2.7 wt% at 80 bar and 298 K, which is the highest number reported for physisorptive materials.

First-Principles study of Ti-Based X2TiH5 (X = Mg, Ca, Sr) hydrides for Advanced hydrogen storage applications

Both from the point of view of global warming and from that of the inevitable exhaustion of Earth’s oil reserve, worldwide interest is focused on using a clean burning substitute such as hydrogen in place of fossil fuels. However the storage of hydrogen is one of the most important challenges impeding its practical application. Metal–organic frameworks (MOFs) are a new emerging class of crystalline porous materials, displaying very low density, significant thermal stability and very high surface area. They offer significant opportunities for hydrogen storage. Therefore, the main objectives of present study were to develop and investigate the synthesis methods, fine structural characterization, and capacity of hydrogen-storage mechanism of MOFs using XRD, FE-SEM/EDS, TEM, BET, TGA, ESCA, high pressure TGA, and XANES/EXAFS techniques. Experimentally, MOFs were synthesized with different metal nitrates in the presence of different solvents combined with organic linkers. The solvothermal method was used to synthesize the MOFs with the reaction temperatures range from 200 to 220oC. These MOFs was named as MIL-53(Cr) having the particle size about 0.5~0.7 μm, respectively identified by FE-SEM microphotos. Since as-synthesized MOFs contain many impurities, it may cause low porosity. Therefore the cleaning methods, such as optimum calcination temperatures or washing several times with different solvents at different warm temperatures were effective and approved to improve higher specific surface area and porosity. The specific surface area of MIL-53(Cr) was 1015 m2/g. N2 adsorption isotherms of MOFs were type I and the distribution of pore diameter curves revealed that MOFs were microporous and mesopores materials. The XRD patterns represented that MOFs had well crystallinity after chemical treatment. The EDS data indicated that MOFs consist of C or O elements and different kinds of metals. The FTIR spectra exhibited vibrational bands in the usual region of 1400~1700 cm-1 for the carboxylic function and 3000~3500 cm-1 for OH- group of these MOFs. TGA curves showed that these MOFs were stable around 200~400oC. XANES/EXAFS spectroscopy was performed to identify the fine structures of MIL-53(Cr). The XANES spectra indicated that the valence of MIL-53(Cr) was Cr(III). The EXAFS data also revealed that MIL-53(Cr) had a first shell of Cr-O bonding with bond distance of 1.96 A and the coordination number was 5.4. The hydrogen storage capacity of MIL-53(Cr) was 0.462 wt%, respectively at 450 psig (30 atm) and room temperature measured using high-pressure thermogravimetric analyzer. In order to improve the hydrogen storage capacity of MOFs, metal/activated carbons were mixed with MOFs. FE-SEM microphotos of Pt/AC and Pd/AC indicated that the particle sizes were 2~5 and 5~10 nm, respectively. By using XPS and XANES spectra, it had found that both Pt and Pd species had zero valency. The EXAFS data revealed that Pt/AC and Pd/AC have a first shell of Pt-Pt and Pd-Pd bonding with bond distances of 2.78 and 2.75 A, respectively. Coordination numbers of both nanoparticles were close to 8 with a FCC structure. The catalytic properties of Pt/AC and Pd/AC were studied for hydrogen spillover in MIL-53(Cr) modified by 5 wt % of catalyst. The hydrogen adsorption capacity of modified MIL-53(Cr) was significantly enhanced up to 0.612 wt% by using the secondary spillover by carbon bridges measured at 450 psig and room temperature. In addition, the adsorption thermodynamic of the data was also confirmed using thermodynamic equations for thermodynamic consistency. Under lower pressures, the adsorption heat is affected by adsorption behaviors. The adsorption heats decrease of increasing adsorption capacities. The adsorption heat of hydrogen onto modified MIL-53(Cr) is < 51 kJ/mol using the secondary spillover of carbon bridges under lower pressures.

Nanoporous metals with considerable specific surface areas and hierarchical pore structures exhibit promising applications in the field of hydrogen storage, electrocatalysis, and fuel cells. In this manuscript, a facile method is demonstrated for fabricating nanoporous Ni with a high surface area by using SiO2 aerogel as a template, i.e., electroless plating of Ni into an SiO2 aerogel template followed by removal of the template at moderate conditions. The effects of the prepared conditions, including the electroless plating time, temperature of the structure, and the magnetism of nanoporous Ni are investigated in detail. The resultant optimum nanoporous Ni with a special 3D flower-like structure exhibited a high specific surface area of about 120.5 m2/g. The special nanoporous Ni exhibited a promising prospect in the field of hydrogen storage, with a hydrogen capacity of 0.45 wt % on 4.5 MPa at room temperature.

Metal-organic frameworks (MOFs) with coordinatively unsaturated metal sites are appealing as adsorbent materials due to their tunable functionality and ability to selectively bind small molecules. Through the use of computational screening methods based on periodic density functional theory, we investigate O2 and N2 adsorption at the coordinatively unsaturated metal sites of several MOF families. A variety of design handles are identified that can be used to modify the redox activity of the metal centers, including changing the functionalization of the linkers (replacing oxido donors with sulfido donors), anion exchange of bridging ligands (considering μ-Br-, μ-Cl-, μ-F-, μ-SH-, or μ-OH- groups), and altering the formal oxidation state of the metal. As a result, we show that it is possible to tune the O2 affinity at the open metal sites of MOFs for applications involving the strong and/or selective binding of O2. In contrast with O2 adsorption, N2 adsorption at open metal sites is predicted to be relatively weak across the MOF dataset, with the exception of MOFs containing synthetically elusive V2+ open metal sites. As one example from the screening study, we predicted that exchanging the μ-Cl- ligands of M2Cl2(BBTA) (H2BBTA = 1H,5H-benzo(1,2-d:4,5-d')bistriazole) with μ-OH- groups would significantly enhance the strength of O2 adsorption at the open metal sites without a corresponding increase in the N2 affinity. Experimental investigation of Co2Cl2(BBTA) and Co2(OH)2(BBTA) confirms that the former exhibits weak physisorption of both N2 and O2, whereas the latter is capable of chemisorbing O2 at room temperature in a highly selective manner. The O2 chemisorption behavior is attributed to the greater electron-donating character of the μ-OH- ligands and the presence of H-bonding interactions between the μ-OH- bridging ligands and the reduced O2 adsorbate.

The possible utilization of hydrogen as the energy source for fuel-cell vehicles is limited by the lack of a viable hydrogen storage system. Metal-organic frameworks (MOFs) belong to a new class of microporous materials that have recently been shown to be potential candidates for hydrogen storage; however, no significant hydrogen storage capacity has been achieved in MOFs at ambient temperature. Here we report substantially increased hydrogen storage capacities of modified MOFs by using a simple technique that causes and facilitates hydrogen spillover. Thus, the storage of 4 wt % is achieved at room temperature and 100 atm for the modified IRMOF-8. The adsorption is reversible, and the rates are fast. That has made MOFs truly promising for hydrogen storage application.

Metal-decorated Tri-graphene as a high-performance reversible hydrogen storage medium: A first-principles study

The fabrication of metal nanoparticles (NP) in porous host matrices, especially metal–organic frameworks (MOFs) has become of great interest in recent years, due to the broad field of applications. In this article we summarize the progress in the field of NP@MOF materials and illustrate the different preparation methods as well as suitable characterisation techniques. Furthermore, practical applications in the fields of hydrogen storage and heterogeneous catalysis are briefly discussed.