Structure and Hydrogen Dynamics of Alkaline Earth Metal Hydrides Investigated with Neutron Scattering

Solid-state proton conductors are highly sought after due to their immense appeal for a variety of energy related applications. Metal hydrides are a type of solid-state hydrogen storage material that can possess the ability for fast ionic transport of hydrogen. Fast kinetics and excellent reversibility are typically desirable properties for applications because the ease of hydrogen storage and retrieval is a key rate limiting step in the operation of functional devices. While some metal hydrides exhibit fast ionic conduction, many are hampered by sluggish hydrogen dynamics. We have chosen three different alkaline earth metal hydrides with vastly different hydrogen kinetics for this investigation, i.e. BaH2 [barium hydride], CaH2 [calcium hydride], and MgH2 [magnesium hydride]. Despite the attractiveness of the high storage densities of MgH2, the hydrogen kinetics are notoriously poor in this material. On the other hand, BaH2 has modest storage densities but exhibits fast ionic conduction that rivals the leading proton and oxide ionic conductors in use today. The motivation of this study is to understand the factors that influence the hydrogen dynamics in these materials. Neutron scattering techniques will be used to probe the atomic scale hydrogen diffusion process and to determine how the crystal structure and hydrogen bonding influence the transport properties.