Ion migration in hydride materials

HighlightsCation and hydride ion conduction in hydride materials offers a niche for solid-state electrolytes.The 15 years of research efforts in this field have led to a variety of promising hydrides that can conduct Li+, Na+, K+, Mg2+, or H− at fast rates in binary hydrides, complex hydrides, and oxyhydrides, among others.A number of approaches in the engineering of hydrides for fast ion conduction at low temperatures have been developed, which include composition alteration in cations or anions and interfacial control through nanocompositing or nanoconfinement. A number of hydride materials have been demonstrated as solid electrolytes for Li/Na all-solid-state batteries.Many hydrides are mixed H− and electronic conductors. Synthesis and development of pure H− conductors would facilitate new types of hydride batteries and fuel cells.Alkaline-earth- and rare-earth-based oxyhydrides are promising candidates for pure H− conduction because of their adjustable compositions, phase transition, relative thermal stability, and good ionic conductivity.AbstractOf particular interest in the present study is ion migration in hydrides. Such motion has profound implications for dynamic H absorption/desorption into/from the lattice of hydrides for hydrogen storage, purification, and separation. The proton/electron transfers from the lattice to its surface for chemical reactions as well as charge transfer across its bulk phase for solid-state electrolytes (SSEs), etc. This progress report presents the recent achievements in alkali/alkaline-earth ion and H− conduction in hydrides. We survey strategic approaches for the design and optimization of these materials for ion conduction, which include anion engineering, cation substitution, complexing, and interfacial engineering. We also briefly discuss the challenges and research directions for hydride-based ion conductors.