High throughput optical characterization of alloy hydrogenation

Transition from the metallic to the hydride phase is of fundamental importance to achieving hydrogen storage in the solid state. Multi-component metal hydrides belong to one of the promising categories of materials that can potentially offer high hydrogen storage capacity. Despite extensive research on metal hydrides over the past decades, the progress remains limited partly due to the inability of screening a nearly infinite number of possible alloy compositions. High throughput materials fabrication and characterization techniques therefore offer an advantage in studying multi-component alloys and their phase transition to metal hydrides. We fabricated an Mg-Ni-Al and Ca-B-Ti ternary alloy libraries using a continuous combinatorial material synthesis technique, and measured the optical reflectance to examine the formation of metal hydride phase when the alloy library was exposed to hydrogen. The results indicate that mapping the change in reflectance is a viable method to study the kinetics of hydride formation. Monitoring the optical properties provides evidence for the "black state" formed during the transition from α-phase to β-phase. In addition, we found that the fastest reflectance change occurred when the alloy has an Mg to Ni ratio of approximately 2:1, and with low concentration of Al.