Fast hydride-ion conduction in complex hydride Ba2MgH6

Abstract

Hydride-ion conductors are required to design hydride-based electrochemical devices for energy conversion and storage. However, developing a hydride-ion conductor with rapid conduction is challenging and has not been explored thoroughly because of the scarcity of hydride materials exhibiting superionic conductivity. In this study, we employed the complex hydride Ba₂MgH₆ as a hydride-ion conductor, which exhibited a superionic conductivity of 0.125 S cm^-1 at 693 K. The superionic state was induced by the formation of the Schottky charge-neutral defect pair of one Ba and two H atoms while maintaining the structural framework. The hydrogen vacancy created at temperatures >625 K facilitated rapid hydride-ion conduction. Density functional theory-based molecular dynamic simulations revealed that defect-free Ba₂MgH₆ does not show hydride-ion conduction, whereas the defective Ba_2−δMgH_6−2δ (Ba vacancy = 0.125) shows rapid hydride-ion conduction along its c-axis. We believe that this superionic conduction in Ba₂MgH₆ induced by Schottky defects will enable the design of superionic hydride-ion conductors via defect engineering.