Metal Hydrides

Abstract

This chapter discusses the various classes of hydride compounds, with a special focus on saline and metallic hydrides as well as oxyhydrides. It includes the following topics: thermodynamic stability, crystal chemistry, synthesis, and physical properties. The chapter also highlights recent progress in understanding hydride ion mobility in alkaline earth hydrides. It further deals with hydride compounds and in particular those containing alkali, alkaline earth, and transition and rare earth metals. The saline hydrides, that is, AH and AeH2(with ALi, Na, K, Rb, and Cs; AeMg, Ca, Sr, and Ba) are proper ionic materials, in which hydrogen is present as hydride anions, H−. Saline hydrides show many similarities with their halide analogues, especially concerning crystal and electronic structures and, perhaps to a lesser extent, physical attributes such as brittleness, hardness, and optical properties.

First-Principles Study of Oxyhydride H– Ion Conductors: Toward Facile Anion Conduction in Oxide-Based Materials

“…Recently, new battery systems based on mobile anions have attracted interest. − In particular, hydride ion may potentially be an attractive charge carrier for electrochemical energy storage, because the high standard redox potential of H 2 /H – (−2.3 V) may lead to high voltage and high energy density . Compared to proton (H + ) conductors widely known in oxide materials, − hydride ion (H – ) conductor is rare and only known in a few metal hydrides − and oxyhydrides. ,− A recent breakthrough study discovered new La 2– x – y Sr x + y LiH 1– x + y O 3– y (0 ≤ x ≤ 1, 0 ≤ y ≤ 2, 0 ≤ x + y ≤ 2) oxyhydrides and demonstrated an exceptionally high H – conductivity of 0.12 mS/cm at 573 K in this material system. , The discovery of the oxyhydrides opens a promising direction for electrochemical solid-state energy storage devices based on H – conduction.…”