Theory, synthesis and characterization of nano-scale architectures for solid-state hydrogen storage
Traditional materials discovery and development techniques have not yet yielded the necessary breakthroughs needed for practical utilization of hydrogen storage. An integrated theoretical-experimental approach to the development of novel materials capable of hydrogen storage under the narrow thermodynamic regime suitable for automotive applications is undertaken.
The viability of engineering two-part nano-architectures (heterostructures) to enhance the binding energy between molecular hydrogen and solid-state nanostructures, or to evince dissociation and uptake of hydrogen into the architecture, was explored. First, exceptional hydrogen uptake (7.5 wt.%) was validated in a metal organic framework compound, MOF-177, at low temperature (77 K), and a thermodynamic model for physisorption was established as a benchmark for all such structures. A chemisorptive pathway for enhanced hydrogen uptake (2.2 wt.%) at room temperature in heterostructures of metal-organic-frameworks (MOFs), via a mechanism now referred to as hydrogen spillover, was experimentally validated and further studied through computations. Ab initio computations at the level of Hartree-Fock (HF) and density functional theories (DFT) made it possible to calculate the thermochemical properties of hydrogen uptake in Pt-doped MOF heterostructures, which verified the thermodynamic plausibility of hydrogen spillover. Furthermore, the hydrogen spillover mechanism was successfully elicited from heterostructures consisting of metal-doped carbon materials, which yielded the highest uptake of hydrogen ever measured at room temperature (8.0 wt.%) for carbon-based material.
The theoretical foundation was formed for a new way of considering how binding interactions between small molecules, such as dihydrogen, and an engineered surface may be influenced by coupling molecular vibrations with low-frequency surface plasmons in clusters of a metal compound. Finally, new MOF-based heterostructures in which a metal dopant is effectively caged within the pore structure were successfully synthesized using a new method of generating metal clusters. These unique structures were specifically engineered to take advantage of hydrogen spillover effects and to overcome the kinetic barriers associated with this mechanism.
The results of this work have provided long-range benefits to the hydrogen storage field. More generally, this research has laid down the groundwork for important spin-off applications in catalysis, nanomaterials, spectroscopy, and plasmonics.