Metal-organic frameworks have received significant attention as a new class of adsorbents for natural gas storage; however, inconsistencies in reporting high-pressure adsorption data and a lack of comparative studies have made it challenging to evaluate both new and existing materials. Here, we briefly discuss high-pressure adsorption measurements and review efforts to develop metal-organic frameworks with high methane storage capacities. To illustrate the most important properties for evaluating adsorbents for natural gas storage and for designing a next generation of improved materials, six metal-organic frameworks and an activated carbon, with a range of surface areas, pore structures, and surface chemistries representative of the most promising adsorbents for methane storage, are evaluated in detail. High-pressure methane adsorption isotherms are used to compare gravimetric and volumetric capacities, isosteric heats of adsorption, and usable storage capacities. Additionally, the relative importance of increasing volumetric capacity, rather than gravimetric capacity, for extending the driving range of natural gas vehicles is highlighted. Other important systems-level factors, such as thermal management, mechanical properties, and the effects of impurities, are also considered, and potential materials synthesis contributions to improving performance in a complete adsorbed natural gas system are discussed. Polarizability 9 2.6Å 3 Volumetric density (1 bar, 25 C) 8 0.9 v/v Volumetric density (250 bar, 25 C) 8 263 v/v Volumetric density (1 bar, À162 C) 8 591 v/v

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.

A techno-economic analysis was conducted for metal–organic framework (MOF) adsorbents, which are promising candidates for light-duty vehicle on-board natural gas and hydrogen storage. The goal of this analysis was to understand cost drivers for large-scale (2.5 Mkg/year) MOF synthesis and to identify potential pathways to achieving a production cost of less than $10/(kg of MOF). Four MOFs were analyzed with four different metal centers and three different linkers: Ni2(dobdc) (dobdc4– = 2,5-dioxido-1,4-benzenedicarboxylate; Ni-MOF-74), Mg2(dobdc) (dobdc4– = 2,5-dioxido-1,4-benzenedicarboxylate; Mg-MOF-74), Zn4O­(bdc)3 (bdc2– = 1,4-benzenedicarboxylate; MOF-5), and Cu3(btc)2 (btc3– = 1,3,5-benzenetricarboxylate; HKUST-1). Baseline costs are projected to range from $35/kg to $71/kg predicated on organic solvent (solvothermal) syntheses using an engineering scale-up of laboratory-demonstrated synthesis procedures and conditions. Two alternative processes were analyzed to evaluate the cost impact of reducing solvent usage: liquid assisted grinding (LAG) and aqueous synthesis. Cost projections from these alternative synthesis approaches range from $13/kg to $36/kg (representing 34–83% reductions), demonstrating the large impact of solvent on the baseline analysis. Finally, sensitivity studies were conducted to identify additional opportunities for achieving MOF production costs of less than $10/kg.

MOFs that exhibit a rare combination of high volumetric and gravimetric densities of stored H2are identified computationally and demonstrated experimentally.