Wolverton Subproject: Hydrogen in Energy and Information Sciences (HEISs)

The Hydrogen in Energy and Information Sciences (HEISs) EFRC aims to advance the fundamental understanding and discovery of multihued hydrogen transport in inorganic solids of earth-abundant elements, and of its transfer along and across interfaces within such materials, where ‘hydrogen’ includes all charge states of the element: H+ (proton), H0 (atom), and H- (hydride ion). The transport characteristics of hydrogen are distinct from those of other elements owing to its small mass, which is comparable to the electronic effective mass of some heavy-Fermion solids, and its ambipolar nature. Dominant transport via tunneling at ambient temperatures is possible for protons, with appreciable kinetic isotope effects. Its redox flexibility, occurring as either a cation or an anion and potentially transforming between states within a given host material, is accompanied by a dramatic change in ionic/atomic radius, from effectively 0 in H+, to 0.6 Å in H0, and 1.1 Å in H-. Furthermore, the hydride ion is far more polarizable than other anions of comparable ionic radius, O2- and F-, suggesting a route to tailor bond covalency and enable high mobility. Beyond its special place in physical chemistry, hydrogen is of tremendous societal importance in energy technologies and of growing importance in energy-efficient computing. In both arenas, the relevant devices are limited by hydrogen kinetics, whether it be electrochemical reaction at an interface or diffusion through the bulk, and whether the material be an electrolyte, a semiconductor, or a metal. HEISs will establish the governing mechanisms and physical descriptors of the transport and interfacial incorporation mechanisms needed to achieve precision-guided discovery and design across these classes of materials. With a deliberate focus on use-inspired, ambient-to-intermediate temperatures, the scientific advances and insights gained will provide a foundation for controlling electrochemical transformations critical for carbon-neutral energy (including nitrogen and carbon dioxide reduction) and for modulating electron transport in materials for brain-inspired computing.