Transporting the hydrogen anion

Hydrogen cation (H⁺) transport is common in both biological systems and engineered ones such as fuel cells. In contrast, the transport of hydrogen anions (H^-) is far less common and is usually coupled with or compromised by the parallel transport of electrons. Kobayashi et al. examined the transport of H^- in a series of rare-earth lithium oxyhydrides (see the Perspective by Yamaguchi). They prevented electronic conduction by using Li⁺ as a countercation. In an electrochemical cell, the oxyhydride material acted as a solid-state electrolyte for H^-, which suggests an alternative avenue for developing energy storage devices.

Abstract

A variety of proton (H⁺)–conducting oxides are known, including those used in electrochemical devices such as fuel cells. In contrast, pure H^- conduction, not mixed with electron conduction, has not been demonstrated for oxide-based materials. Considering that hydride ions have an ionic size appropriate for fast transport and also a strong reducing ability suitable for high-energy storage and conversion devices, we prepared a series of K₂NiF^4-type oxyhydrides, La_2-x-y2Sr_x+yLiH_1-x+yO_3-y, in the hope of observing such H^- conductors. The performance of an all-solid-state TiH₂/o-La₂LiHO₃ (x = y = 0, o: orthorhombic)/Ti cell provided conclusive evidence of pure H^- conduction.

Science 18 Mar 2016:
Vol. 351, Issue 6279, pp. 1314-1317
DOI: 10.1126/science.aac9185

http://science.sciencemag.org/content/351/6279/1314