[Perspective] Large, soft, and polarizable hydride ions sneak around in an oxyhydride
Ionic conductivity in solids, a field initiated by Faraday (1), has led to materials that help chemists spatially separate the oxidation and reduction steps of reactions, enabling technologies such as fuel cells. Many solid oxides are good oxygen ion (O2−) conductors, but getting hydrogen ions, either protons (H+) or hydride anions (H−), to conduct through oxides has been a major challenge. A proton-conducting oxide reported in 1981 (2) marked the beginning of “oxide protonics,” a materials science based on solid solutions of oxides and hydroxides. On page 1314 of this issue, Kobayashi et al. (3) report a material with pure H− conductivity (and yet an electronic insulator) in an oxyhydride system, which has been a “last frontier” in solid state ionics. Author: Shu Yamaguchi