The potential commercial applications for metal organic frameworks (MOFs) are tantalizing. To address the opportunity, many novel approaches for their synthesis have been developed recently. These strategies present a critical step towards harnessing the myriad of potential applications of MOFs by enabling larger scale production and hence real-world applications. This review provides an up-to-date survey ( references) of the most promising novel synthetic routes, i.e., electrochemical, microwave, mechanochemical, spray drying and flow chemistry synthesis. Additionally, the essential topic of downstream processes, especially for large scale synthesis, is critically reviewed. Lastly we present the current state of MOF commercialization with direct feedback from commercial players.
One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.
The Materials Genome is in action: the molecular codes for millions of materials have been sequenced, predictive models have been developed, and now the challenge of hydrogen storage is targeted. Renewably generated hydrogen is an attractive transportation fuel with zero carbon emissions, but its storage remains a significant challenge. Nanoporous adsorbents have shown promising physical adsorption of hydrogen approaching targeted capacities, but the scope of studies has remained limited. Here the Nanoporous Materials Genome, containing over 850 000 materials, is analyzed with a variety of computational tools to explore the limits of hydrogen storage. Optimal features that maximize net capacity at room temperature include pore sizes of around 6 Å and void fractions of 0.1, while at cryogenic temperatures pore sizes of 10 Å and void fractions of 0.5 are optimal. Our top candidates are found to be commercially attractive as “cryo-adsorbents”, with promising storage capacities at 77 K and 100 bar with 30% enhancement to 40 g/L, a promising alternative to liquefaction at 20 K and compression at 700 bar.
Porosity loss, also known as physical aging, in glassy polymers hampers their long term use in gas separations. Unprecedented interactions of porous aromatic frameworks (PAFs) with these polymers offer the potential to control and exploit physical aging for drastically enhanced separation efficiency. PAF-1 is used in the archetypal polymer of intrinsic microporosity (PIM), PIM-1, to achieve three significant outcomes. 1) hydrogen permeability is drastically enhanced by 375% to 5500 Barrer. 2) Physical aging is controlled causing the selectivity for H2 over N2 to increase from 4.5 to 13 over 400 days of aging. 3) The improvement with age of the membrane is exploited to recover up to 98% of H2 from gas mixtures with N2 . This process is critical for the use of ammonia as a H2 storage medium. The tethering of polymer side chains within PAF-1 pores is responsible for maintaining H2 transport pathways, whilst the larger N2 pathways gradually collapse.
Gas separation technologies for carbon-free hydrogen and clean gaseous fuel production must efficiently perform the following separations: (1) H 2 /CO 2 (and H 2 /N 2 ) for pre-combustion coal gasification, (2) CO 2 /N 2 for post-combustion of coal, (3) CO 2 /CH 4 for natural gas sweetening and biofuel purification, and (4) O 2 /N 2 for oxy-combustion of coal. By utilizing a molecular simulation approach, Monte Carlo procedures, free volume analysis, and continuum modeling, we predict the intrinsic gas permeability and separation properties of several new Zeolitic Imidazolate Frameworks (ZIFs), a family of the Metal-Organic Frameworks (MOFs). The well defined pore sizes in conjunction with high surface areas make ZIFs prime candidates for molecular sieving. In this work, our calculated intrinsic properties are compared with current experimental results where ZIFs are either grown in dense layers to form pure inorganic membranes on porous supports or dispersed within a polymer phase to form mixed matrix membranes. Consequently, this paper assesses current membrane development according to industrial feasibility targets and highlights the achievable superior separation results for ideal membrane configurations. For example, ZIF-11 is discovered to be capable of sieving H 2 from all of its larger gas counterparts at a remarkable H 2 /CO 2 selectivity of 262 and H 2 permeability of 5830 Barrer, well within the target area for efficient hydrogen production.
To generate metal-organic frameworks (MOFs) that are complex and modular yet well ordered, we present a strategy employing a family of three topologically distinct linkers that codes for the assembly of a highly porous quaternary MOF. By introducing substituted analogues of the ligands, a set of eight isoreticular frameworks is delivered, with the MOF structure systematically varied while the topology is maintained. To combat randomness and disorder, the substitution patterns of the ligands are designed to be compatible with their crystallographic site symmetries. MOFs produced in this way feature "programmed pores"--multiple functional groups compartmentalized in a predetermined array within a periodic lattice--and are capable of complex functional behavior. In these examples unconventional CO2 sorption trends, including capacity enhancements close to 100%, emerge from synergistic effects. Future PP-MOFs may be capable of enzyme-like heterogeneous catalysis and ultraselective adsorption.
The first crystalline beryllium-based metal-organic framework has been synthesized and found to exhibit an exceptional surface area useful for hydrogen storage. Reaction of 1,3,5-benzenetribenzoic acid (H(3)BTB) and beryllium nitrate in a mixture of DMSO, DMF, and water at 130 degrees C for 10 days affords the solvated form of Be(12)(OH)(12)(1,3,5-benzenetribenzoate)(4) (1). Its highly porous framework structure consists of unprecedented saddle-shaped [Be(12)(OH)(12)](12+) rings connected through tritopic BTB(3-) ligands to generate a 3,12 net. Compound 1 exhibits a BET surface area of 4030 m(2)/g, the highest value yet reported for any main group metal-organic framework or covalent organic framework. At 77 K, the H(2) adsorption data for 1 indicate a fully reversible uptake of 1.6 wt % at 1 bar, with an initial isosteric heat of adsorption of -5.5 kJ/mol. At pressures up to 100 bar, the data show the compound to serve as an exceptional hydrogen storage material, reaching a total uptake of 9.2 wt % and 44 g/L at 77 K and of 2.3 wt % and 11 g/L at 298 K. It is expected that reaction conditions similar to those reported here may enable the synthesis of a broad new family of beryllium-based frameworks with extremely high surface areas.
Lithium-sulfur batteries can displace lithium-ion by delivering higher specific energy. Presently, however, the superior energy performance fades rapidly when the sulfur electrode is loaded to the required levels—5 to 10 mg cm−2— due to substantial volume change of lithiation/delithiation and the resultant stresses. Inspired by the classical approaches in particle agglomeration theories, we found an approach that places minimum amounts of a high-modulus binder between neighboring particles, leaving increased space for material expansion and ion diffusion. These expansion-tolerant electrodes with loadings up to 15 mg cm−2 yield high gravimetric (>1200 mA·hour g−1) and areal (19 mA·hour cm−2) capacities. The cells are stable for more than 200 cycles, unprecedented in such thick cathodes, with Coulombic efficiency above 99%.
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