General Techniques for Increasing Packing Density of Metal-Organic Frameworks for Enhanced Volumetric Storage of Hydrogen

Current hydrogen fuel cell electric vehicles (FCEVs) on the market rely on high-pressure hydrogen, 700 bar, storage systems to store and deliver hydrogen for use in the fuel cell. Bringing hydrogen to high pressures and storing hydrogen at high-pressure requires sophisticated compressors and specialized carbon wrapped tanks, respectively. This high-pressure constraint makes FCEVs vehicles challenging and expensive to implement at scale, with costs passed onto the end user. This cost is coupled with safety concerns, with equipment failure in the supply chain leading to the release of high-pressure flammable gas that would present significant hazards. Therefore, alternative technologies that could facilitate the storage of hydrogen at lower pressure are required if hydrogen cars are going to be widely adopted by the public. Porous materials, in particular, metal-organic frameworks (MOFs), have been highlighted as materials that could be used to store and deliver hydrogen at lower pressures in FCEVs. One of the key drawbacks of these materials that is often overlooked in the academic literature is their poor volumetric packing. Low volumetric packing of these systems results in smaller amounts of adsorption per unit volume. Volumetric packing is of critical importance for fuel tank applications where storage space is limited. Therefore, to realize the potential of MOFs, the packing density of MOFs must be optimized before these materials can be used in FCEVs. For this reason, the purpose of this SBIR proposed by NuMat Technologies (NuMat) is to develop generalizable techniques for increasing the volumetric packing density of MOFs. The methods developed are transferable to other MOFs, are scalable, and will occur with no loss of performance. Towards achieving this goal through Phase I work, NuMat successfully evaluated several packing techniques on a small scale optimizing the volumetric packing density of several MOFs. The goal of eighty percent packing density outlined in Phase I, without altering the performance of the material, was achieved and results were shown to be transferable across a group of MOFs. Under Phase II, NuMat proposes to transition these formation techniques to commercial scales, identifying and validating the required equipment. Furthermore, high-density prototypes will be developed, and the tradeoff between high-packing density and other important parameters including the rates of adsorption and desorption will be understood. The results achieved here will allow for MOFs to be implemented in FCEVs storage systems, which could bring reductions in the cost of these systems and improvements in safety. Removing high-pressure constraints currently in place would simplify storage systems, allowing for complex infrastructure to be simplified. These improvements will reduce the cost of FCEVs and alleviate safety concerns about the storage of hydrogen at high-pressure, making these vehicles competitive with gasoline vehicles. The work carried out by NuMat under this SBIR is broadly applicable to a wide range of volumetric storage challenges that are commercially relevant including the storage of light hydrocarbons for transportation, oxygen storage for medical applications, and safe transportation and delivery of toxic gases.