Ba₂ScHO₃: H^– Conductive Layered Oxyhydride with H^– Site Selectivity

Abstract

Hydride (H–) conduction is a new frontier related to hydrogen transport in solids. Here, a new H– conductive oxyhydride Ba2ScHO3 was successfully synthesized using a high-pressure technique. Powder X-ray and neutron diffraction experiments investigated the fact that Ba2ScHO3 adopts a K2NiF4-type structure with H– ions preferentially occupying the apical sites, as supported by theoretical calculations. Electrochemical impedance spectra showed that Ba2ScHO3 exhibited H– conduction and a conductivity of 5.2 × 10–6 S cm–1 at 300 °C. This value is much higher than that of BaScO2H, which has an ideal perovskite structure, suggesting the advantage of layered structures for H– conduction. Tuning site selectivity of H– ions in layered oxyhydrides might be a promising strategy for designing fast H– conductors applicable for novel electrochemical devices.