Hydrogen Storage In Metal-organic Frameworks Research Articles

An Assessment of Metal-Organic Frameworks and Activated Carbon Solutions for Sustainable Hydrogen Gas Storage

The pursuit of sustainable energy sources has elevated hydrogen gas as a potential carbon-neutral fuel with high energy content. However, efficient storage and transportation of hydrogen pose considerable challenges. To address these issues, the utilisation of metal-organic frameworks (MOFs) and activated carbon (AC) for hydrogen storage through adsorption has gained substantial attention. This research article offers a comprehensive assessment of hydrogen storage using these materials.
 The adsorption mechanism, fundamental to hydrogen storage in MOFs, involves hydrogen molecules adhering to the MOF framework's surface and pores via intermolecular forces. MOFs, comprising metal nodes and organic linkers, present high surface area-to-volume ratios and customizable adsorption properties, making them appealing for gas storage. AC, an amorphous porous carbon form, also displays favourable traits for gas storage.

Prediction of hydrogen storage in metal-organic frameworks: A neural network based approach

Gas capture, sensing, and storage systems are all within the capabilities of metal–organic frameworks (MOFs). It is common practise to choose the MOF with the best adsorption property from a large database before running an adsorption calculation. High-throughput computational research is sometimes hampered by the expense of computing thermodynamic values, slowing the progress of MOFs for separations and storage applications. When trying to predict material properties, machine learning has recently emerged as a possible alternative to more conventional methods like experiments and simulations. The H2 capacities of 918,734 MOFs drawn from 19 databases were recently predicted using ML by Ahmed and Siegel (2021). Several ML methods were utilized, and the extremely randomised tree (ERT) model emerged as the most accurate predictor of hydrogen delivery capacity in terms of both gravimetric and volumetric quantities. Interestingly we have used deep learning model (Feed-forward neural network) as well as ERT model for the prediction of H2 deliverable capacities of a huge number of MOFs developed from the previous studies and got till date best results for predictions. To verify our model’s efficacy, we also performed Grand Canonical Monte Carlo (GCMC) simulations. We show our method by forecasting the hydrogen storage capacity of MOFs during a temperature and pressure swing from 100bar/77K to 5bar/160K.

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

In order to enhance the hydrogen storage capacity of Metal-Organic Frameworks (MOFs) under moderate conditions, a high-throughput screen was used to evaluate 7622 MOFs with a Pore Limit Diameter (PLD) greater than 2.89 Å and less than 10 Å. The hydrogen adsorption capacity at 25 °C and 1 bar was calculated using grand canonical Monte Carlo (GCMC) to comprehensively evaluate the effect of pore structure characteristics on the hydrogen storage capacity of MOFs. The optimal composite mass ratio between carbon-based materials, transition metals, and MOFs was determined by Density Functional Theory (DFT). The mechanism of hydrogen spillover affecting the hydrogen storage capacity of MOFs was analyzed by preparation, characterization, and hydrogen adsorption capacity testing. To further enhance the hydrogen storage capacity of MOFs composites and improve the kinetic properties and reversibility of metal hydrides, aluminum hydride (AlH3) was nano-confined in MOF@carbon matrix material@transition metal to form new nano-confined composites with improved dehydrogenation temperature and reduced reversibility conditions. The results showed that MOFs with a PLD in the range of 7–10 Å, porosity in the range of 0.75–0.90, and pore volume in the range of 1.4–2.2 cm3/g possess high hydrogen storage capacity. Compared to pristine MOFs, the hydrogen storage capacity of the composites with induced hydrogen spillover is at least 5 times higher. The new composites with improved kinetic hydrogen release characteristics after nano-confined AlH3 achieve reversible hydrogen release at 150 °C and 70 bar.

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

Metal organic frameworks (MOFs) have been studied vastly for hydrogen storage purposes due to their unique properties. In the present work hydrogen storage capacity is modeled using machine learning approaches including Multi-layer Perceptron (MLP), Support Vector Machines (SVM), Random Forest (RF), CatBoost, LightGBM, XGBoost, and Committee Machine Intelligence System (CMIS) trained on experimental data gathered from various experimental studies. CMIS model shows the best results with R2=0.982 and Root Mean Square Error = 0.088. Additionally, this study uses the Leverage method to detect and eliminate suspected data points in order to improve predictability. Only 2.04% of data points are detected as suspected data points. Sensitivity analysis demonstrates that surface area, pore volume, pressure, and temperature have almost the same contribution on hydrogen storage. The findings of this research offer a valuable model for MOF selection and optimization of operational conditions in hydrogen storage processes that utilizes MOFs.

Strategies for the Improvement of Hydrogen Physisorption in Metal-Organic Frameworks and Advantages of Flexibility for the Enhancement

To overcome the environmental issues arising from the burning of fossil fuel, an alternative effective source of energy is required. Hydrogen energy is one such alternative which can pave the purpose of interest. For a successive replacement of fossil fuel by hydrogen energy, hydrogen storing, especially in a vehicular system, is highly required and it is still a major challenge. A wide range of materials have been used for hydrogen storing. Metal-organic framework is one of them, which have been studied extensively both from academic and industrial viewpoint. These studies show that several metal-organic frameworks (MOFs) have excellent physisorption ability but normally at a very low temperature. To improve this at ambient conditions, various strategies have been introduced so far for MOFs, although an important aspect of external stimuli-responsive flexible or dynamic frameworks, have not been studied systematically. There are various advantages of the use of dynamic MOFs for hydrogen physisorption and sometimes helpful to overcome socio-economical barrier connected to this alternative energy source. In this highlight, prior strategies to improve hydrogen storage in MOF with special importance on external stimuli-responsive flexible MOF and their perspective importance in hydrogen storage have been discussed.

Optimizing Hydrogen Storage in MOFs through Engineering of Crystal Morphology and Control of Crystal Size.

Metal-organic frameworks (MOFs) are promising materials for hydrogen storage that fail to achieve expected theoretical values of volumetric storage density due to poor powder packing. A strategy that improves packing efficiency and volumetric hydrogen gas storage density dramatically through engineered morphologies and controlled-crystal size distributions is presented that holds promise for maximizing storage capacity for a given MOF. The packing density improvement, demonstrated for the benchmark sorbent MOF-5, leads to a significant enhancement of volumetric hydrogen storage performance relative to commercial MOF-5. System model projections demonstrate that engineering of crystal morphology/size or use of a bimodal distribution of cubic crystal sizes in tandem with system optimization can surpass the 25 g/L volumetric capacity of a typical 700 bar compressed storage system and exceed the DOE targets 2020 volumetric capacity (30 g/L). Finally, a critical link between improved powder packing density and reduced damage upon compaction is revealed leading to sorbents with both high surface area and high density.

Predicting hydrogen storage in MOFs via machine learning

SummaryThe H2 capacities of a diverse set of 918,734 metal-organic frameworks (MOFs) sourced from 19 databases is predicted via machine learning (ML). Using only 7 structural features as input, ML identifies 8,282 MOFs with the potential to exceed the capacities of state-of-the-art materials. The identified MOFs are predominantly hypothetical compounds having low densities (<0.31 g cm−3) in combination with high surface areas (>5,300 m2 g−1), void fractions (∼0.90), and pore volumes (>3.3 cm3 g−1). The relative importance of the input features are characterized, and dependencies on the ML algorithm and training set size are quantified. The most important features for predicting H2 uptake are pore volume (for gravimetric capacity) and void fraction (for volumetric capacity). The ML models are available on the web, allowing for rapid and accurate predictions of the hydrogen capacities of MOFs from limited structural data; the simplest models require only a single crystallographic feature.

Screening Study of the Effects of Impurity Gases on Hydrogen Storage in Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are perhaps one of the promising candidates for H2 storage in a fuel cell vehicle. However, impurity gases, such as H2O, CO2, CH4, O2, and N2 existing in the process of H2 production, have a detrimental impact on H2 storage. In the present work, the process of H2 with and without impurity gases (i.e., H2O, CO2, CH4, O2, and N2) adsorption in 95 MOFs is screened by molecular simulation. The effect of a low concentration of impurity gases on the H2 delivery capacity is studied. The results show that the effect of impurity gases on the H2 delivery capacity of 95 MOFs ranks as H2O>CO2>CH4>O2=N2. DIDDOK is demonstrated to exhibit the best gravimetric delivery capacity of H2, and ANUGIA exhibits the best volumetric delivery capacity of H2. These results show that one should consider impurity gas effects during screening the best adsorbent for H2 storage in fuel cell vehicles.

Mathematical modeling of interaction energies between nanoscale objects: A review of nanotechnology applications

In many nanotechnology areas, there is often a lack of well-formed conceptual ideas and sophisticated mathematical modeling in the analysis of fundamental issues involved in atomic and molecular interactions of nanostructures. Mathematical modeling can generate important insights into complex processes and reveal optimal parameters or situations that might be difficult or even impossible to discern through either extensive computation or experimentation. We review the use of applied mathematical modeling in order to determine the atomic and molecular interaction energies between nanoscale objects. In particular, we examine the use of the 6-12 Lennard-Jones potential and the continuous approximation, which assumes that discrete atomic interactions can be replaced by average surface or volume atomic densities distributed on or throughout a volume. The considerable benefit of using the Lennard-Jones potential and the continuous approximation is that the interaction energies can often be evaluated analytically, which means that extensive numerical landscapes can be determined virtually instantaneously. Formulae are presented for idealized molecular building blocks, and then, various applications of the formulae are considered, including gigahertz oscillators, hydrogen storage in metal-organic frameworks, water purification, and targeted drug delivery. The modeling approach reviewed here can be applied to a variety of interacting atomic structures and leads to analytical formulae suitable for numerical evaluation.

Hydrogen Storage in Metal-Organic Frameworks: A Review

Metal-organic frameworks (MOFs) for hydrogen storage have continued to receive intense interest over the past decade. MOFs are a class of organic-inorganic hybrid crystalline materials consisting of metallic moieties that are linked by strong coordination bonds to organic ligands. They exhibit a great structural diversity and possess low weight, exceptionally high surface areas, large free volumes, and tunable pore sizes and functionalities, making them extremely attractive for a variety of applications such as hydrogen storage. For these reasons MOFs have been extensively studied. In this paper, a review of recent developments on hydrogen storage in MOFs is presented, with a focus on the effects of various factors including open metal sites, ‘guest’ metal ions, ligand functionalization, surface area, pore volume, pore size, and Pt or Pd metal nanoparticles, on hydrogen storage. In addition, the review examines the emerging research on MOF hybrid hydrogen storage systems, primarily in the context of employing MOFs for nanoconfinement of high temperature hydrogen storage materials. The review focuses on experimental studies.

Hydrogen Storage in Metal-Organic Frameworks

Understanding of the physisorption of H2 in metal-organic frameworks (MOFs) is critical to improving its performance for hydrogen storage. By using first-principles calculations employing the van der Waals density functional (vdW-DF) method which can properly describe the vdW interaction, we investigate the binding energy of H2 in MOF-5 crystal. The accuracy of this methodology is first examined and good accuracy comparable to the correlated wavefunction methods is found. Calculations for the true crystal structure show that the small fragment models used in previous calculations cannot represent well the property of the crystal. The good accuracy and the ability to deal with the true crystal structure make the vdW-DF method a good candidate for investigating hydrogen storage in MOFs.

Lithium doping on metal-organic frameworks for enhancing H 2 Storage

Hydrogen storage in metal-organic frameworks (MOFs) is an important and hot topic in hydrogen economics. Unfortunately, no one virgin MOF material can meet the requirement of the U.S. Department of Energy (DOE) by now. Thus, many strategies for enhancing hydrogen uptake have been proposed. Recently, both experimental and theoretical researches indicate that H 2 adsorption capacities of MOFs could be enhanced via doping alkali metal cations to the frameworks, particularly Li +, owing to the strong affinity of Li + for H 2 molecules. Here, we synthesize Li•Cu 3(BTC) 2, and Li•MIL-101 (Cr) by using lithium naphthalenide and further investigate the H 2 sorption capacities of these materials. It is found that at 77 K and 1 bar, the H 2 uptakes of Cu 3(BTC) 2 and MIL-101 (Cr) are increased by 45% and 43%, respectively, after doping lithium, which indicates that the lithium doping does provide an effective approach for enhancing H 2 uptakes.

Hydrogen Storage in Metal–Organic Frameworks

Metal-organic frameworks (MOFs) are highly attractive materials because of their ultra-high surface areas, simple preparation approaches, designable structures, and potential applications. In the past several years, MOFs have attracted worldwide attention in the area of hydrogen energy, particularly for hydrogen storage. In this review, the recent progress of hydrogen storage in MOFs is presented. The relationships between hydrogen capacities and structures of MOFs are evaluated, with emphasis on the roles of surface area and pore size. The interaction mechanism between H(2) and MOFs is discussed. The challenges to obtain a high hydrogen capacity at ambient temperature are explored.

Role of Exposed Metal Sites in Hydrogen Storage in MOFs

The role of exposed metal sites in increasing the H2 storage performances in metal-organic frameworks (MOFs) has been investigated by means of IR spectrometry. Three MOFs have been considered: MOF-5, with unexposed metal sites, and HKUST-1 and CPO-27-Ni, with exposed Cu(2+) and Ni(2+), respectively. The onset temperature of spectroscopic features associated with adsorbed H2 correlates with the adsorption enthalpy obtained by the VTIR method and with the shift experienced by the H-H stretching frequency. This relationship can be ascribed to the different nature and accessibility of the metal sites. On the basis of a pure energetic evaluation, it was observed that the best performance was shown by CPO-27-Ni that exhibits also an initial adsorption enthalpy of -13.5 kJ mol(-1), the highest yet observed for a MOF. Unfortunately, upon comparison of the hydrogen amounts stored at high pressure, the hydrogen capacities in these conditions are mostly dependent on the surface area and total pore volume of the material. This means that if control of MOF surface area can benefit the total stored amounts, only the presence of a great number of strong adsorption sites can make the (P, T) storage conditions more economically favorable. These observations lead to the prediction that efficient H2 storage by physisorption can be obtained by increasing the surface density of strong adsorption sites.

Is catenation beneficial for hydrogen storage in metal–organic frameworks?

Grand canonical Monte Carlo (GCMC) simulations demonstrate that catenation can be beneficial for improving hydrogen storage in metal-organic frameworks at cryogenic temperatures and low pressures but not necessarily at room temperature.