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 K2NiF4-type oxyhydrides, La2-x-y2Srx+yLiH1-x+yO3-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