The on-board storage of hydrogen represents a roadblock to using it as fuel for automobiles. "Dissolving" gaseous hydrogen into solid metals or compounds holds promise for safe, high-density storage. The best storage materials will also be capable of high rates at which hydrogen can be stored and retrieved. The difficulty of evaluating candidate storage materials is complicated by a lack of readily available methods for the direct measurement of hydrogen content.
Researchers from MML, NCNR, and PML, are working together to provide measurement tools to fill this gap. Prompt Gamma Activation Analysis (PGAA) is a direct method for measuring hydrogen, but is not commonly accessible since it requires a source of neutrons. Infrared (IR) and Raman imaging/spectroscopy methods, being developed at NIST, could be made widely available, but are not capable of directly measuring hydrogen content. By correlating measurements of hydrogen content using PGAA with Infrared and Raman imaging/spectroscopy methods, we will provide an accurate screening method widely usable by industry with the high spatial resolution needed for combinatorial development of storage materials.
We have chosen magnesium-based alloys to develop the combinatorial methods needed to assess hydrogen storage. Magnesium alloys are candidates for hydrogen storage since magnesium hydride has a high reversible storage capacity of 7.6 wt% hydrogen, which is high enough to meet DoE's short-term goals for hydrogen-powered vehicles. We have prepared gradient MgxNi1-x films with palladium overlayers (to prevent oxidation and catalyze hydrogen uptake) of varying thickness (0 < t < 20 nanometers) in the direction orthogonal to the composition gradient. We have demonstrated the local hydrogenation within the films with an IR detector, with changes in infrared intensity corresponding to hydrogen accommodation. The efforts will enable a combinatorial approach to analyze, in one experiment on a single substrate, the effects of varying microstructure, changing composition, and thickness of catalyst on the hydrogenation capabilities of the films using IR and Raman. Correlation of these results with PGAA is underway.