Physics and Astronomy Calendar

Hydrogen storage remains one of the main challenges in the implementation of a hydrogen based energy economy. Although several different approaches are being pursued, sorption onto a porous high surface area material is a leading contender. Remarkably, recent experiments using the spillover method are operating at room temperature, and are approaching the real-world targets as set by the Department of Energy for potential use in fuel cell cars. Spillover works by using nanoscale metal catalysts distributed through the porous substrate material to break the hydrogen molecules into atomic hydrogen which then attaches to the substrate. The best results have been on metal-organic framework materials.

The sample preparation for these hydrogen spillover experiments is quite complex, and there has been significant scatter in the experimental results. Without clear predictions for saturation storage capacities, it has been difficult to evaluate the experimental results. It has also been difficult to improve the early and best results.

In this project, accurate predictions for saturation storage density at room temperature for a wide range of experimentally interesting materials will be determined using quantum chemistry calculations of binding energies for individual and multiple hydrogen atoms on model molecules. Instead of estimates based on surface area, we are counting specific binding sites on the crystal surface. Our current work shows that many of the experimental results are a factor of 3 below theoretical predictions. Therefore, these materials require further improvement in sample preparation in order to achieve their full hydrogen storage potential.

The project will also test new materials to improve storage density above useful DOE targets and to improve substrate durability. Preliminary work suggests that new metal-organic and covalent-organic substrate materials can have saturation storage densities above 6 wt%. Issues of lattice shrinkage and strain will also be addressed. New materials have also been proposed that are more resistant to water. Rolled and modified graphene based materials will also be investigated for their hydrogen storage potential.

These studies have a direct application to ongoing hydrogen storage experiments by spillover. Together the theory and experiment provide an exciting path forward for hydrogen storage at room temperature. Existing experimental results for spillover on IRMOF-8 with bridge building have provided the best storage results within the sorption framework at room temperature. The ability to provide significant sorption capability at room temperature is a giant step forward. These avenues provide an opportunity to meet or exceed the Department of Energy targets for useful hydrogen storage for mobile and transport applications of 6.5 wt %.