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

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, LaH_3-2O 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^-.