Room-Temperature Fast H^– Conduction in Oxygen-Substituted Lanthanum Hydride

Abstract

The hydride ion (H–) is a unique anionic species that exhibits high reactivity and chemical energy. H– conductors are key materials to utilize advantages of H– for applications, such as chemical reactors and energy storage systems. However, low H– conductivity at room temperature (RT) in current H– conductors limit their applications. In this study, we report a H– conductivity of ∼1 mS cm–1 at RT, which is higher by 3 orders of magnitude than that of the best conductor, in lightly oxygen-doped lanthanum hydride, LaH3–2x O x with x < 0.25. The oxygen concentration (x) is crucial in achieving fast H– conduction near RT; the low activation barrier of 0.3–0.4 eV is attained for x < 0.25, above which it increases to 1.2–1.3 eV. Molecular dynamics simulations using neural-network potential successfully reproduced the observed activation energy, revealing the presence of mobile and immobile H–.

Expanding the hydride chemistry: antiperovskites A3MO4H (A = Rb, Cs; M = Mo, W) introducing the transition oxometalate hydrides

“…[9][10][11] The latter are typically synthesized by high pressure synthesis or reductive topotactic reaction which oen leads to materials with disordered anions such as AECrO 2 H (AE ¼ Sr, Ba) 10,11 or BaTiO 3Àx H x 12,13 as archetypical examples. Undoubtedly, transition metal-based oxy hydrides show fascinating characteristics on their own such as magnetic ordering at elevated temperatures 10,11,14 diffusional dynamics, 15 good electronic 13,16 or ionic 17 conductivities. However, yet no single hydridic compound containing complex transition orthooxometalate anions such as tetrahedral MoO 4 2À or WO 4 2À anions has been reported.…”

Aliovalent Calcium Doping of Yttrium Oxyhydride Thin Films and Implications for Photochromism

“…Not only are the octahedral H – likely the first to leave the structure upon oxidation, 3 , 32 but they are often cited as more mobile than tetrahedral H – either due to the lower formation energy for an octahedral H vacancy 14 or their weaker electrostatic interactions with O 2– (more distance). 47 Having these mobile H – could be an essential ingredient to the formation and dissolution of a “darkened” phase.…”

“…On the other hand, there can be a large difference in the properties of octahedral versus tetrahedral H – , making the decrease in the population of certain H – potentially significant for the observed properties of the material. Not only are the octahedral H – likely the first to leave the structure upon oxidation, , but they are often cited as more mobile than tetrahedral H – either due to the lower formation energy for an octahedral H vacancy or their weaker electrostatic interactions with O 2– (more distance) . Having these mobile H – could be an essential ingredient to the formation and dissolution of a “darkened” phase.…”

High Proton Conduction in Ba2LuAlO5 with Highly Oxygen Deficient Layers

“…In addition, materials that function at such low temperatures require expensive precious metal catalysts when used in fuel cells 12,13 . Hydride (H − ) ion conductors have been considered to be a new option, with some examples showing high conductivity at low temperatures [14][15][16] . However, they have drawbacks such as being prone to decomposition at high temperatures or can only be synthesized by the high-pressure method 15,17 .…”