This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Metal-organic frameworks (MOFs) are potential candidates for H2 storage because they can reversibly absorb hydrogen at low temperatures. The critical issue is their low hydrogen capacity at room temperature or above, because the interaction between molecular hydrogen and MOFs is weak. Very recently, however, it was found that hydrogen capacities of MOFs can be increased by almost 10 times via atomic hydrogen adsorption. Currently, introduction of atomic hydrogen into MOFs is based on a catalytic method via a secondary spillover approach: hydrogen molecules are first dissociate into atoms on Pt metal catalyst, followed by the primary spillover of atomic hydrogen onto the surface of an activated carbon support. Then, the hydrogen atoms present on activated carbon migrate via a secondary spillover to the MOF surface. It was demonstrated that the hydrogen adsorption and desorption kinetics are strongly dependent on the carbon bridge between the Pt and the MOF, which controls the atomic hydrogen migration between them. The goal of this project is to accelerate the hydrogen adsorption and desorption by directly supporting metal catalysts on MOFs without carbon bridges. The specific hypothesis is that the migration of hydrogen atoms generated on catalyst directly to the MOF via a primary spillover should be much faster than that of atomic hydrogen from the catalyst to the MOF with carbon bridges. We based the hypothesis on the observations that 1) hydrogen adsorption and dissociation on Pt catalyst are fast, whereas the spillover of hydrogen from Pt metal to its support is a slow process, 2) when hydrogen concentration on surface increases, its spillover decreases, and 3) the migration of atomic hydrogen is faster on MOFs than on carbon materials. Based on these observations, the experimental focus of this proposal is on the bondings and spillover of atomic hydrogen on TM/MOF materials (TM=Pt, Pd, Rh, Ru, or Ni). The specific aims are to: (1) to examine the effects of spillover-steps on kinetics of hydrogen adsorption and desorption of MOFs; (2) to evaluate the bondings and migration of atomic hydrogen on MOFs; (3) to examine the effect of atomic hydrogen adsorption on crystal structures of MOFs; and (4) to evaluate new TM/MOF materials for hydrogen adsorption and desorption as well as cyclability.
This research has significant intellectual merit. The interaction between the atomic hydrogen and MOFs has not been studied experimentally, even almost not theoretically. Such an interaction will be subjected to a comprehensive assessment in this project, which can provide useful information for designing MOF-based hydrogen storage materials, separation membranes, adsorbents, and hydrogenation catalysts. Knowledge about the spillover of adsorbed species at high pressure is not available, because current information regarding the spillover on catalysts was obtained from low-pressure experiments. The evaluation of hydrogen spillover at high pressure by using in-situ FTIR in this project will provide useful information to understand heterogeneous catalytic mechanisms of important industrial processes, most of which are based on high pressure catalytic reactions.
This project can have a broad impact. The highly effective storage materials, which will be developed here, can lead to the decrease of hydrogen storage cost and will impact commercial feasibility of fuel cell vehicles, thus reducing requirement of oil. The knowledge about atomic hydrogen spillover and adsorption can impact development of catalysts for chemical industries. This project has also strong impacts on the education of students. A special program "Summer Institute in Hydrogen Energy" will be created. It will promote the technology of hydrogen energy into high school science classrooms via training high school teachers. This would increase female students in science and engineering schools of colleges, because high school teachers have a tremendous impact on their students' future interests and pursuits. Furthermore, two graduate and one undergraduate students will work as important part of a diverse team, and they will gain hands-on experience designing, building, and running complex experiments. In addition, this project can increase their abilities to accept high school students as summer interns for renewable energy studies.
