Hydride ion (H^-) transport behavior in barium hydride under high pressure

Hydride ions (H^-) have an appropriate size for fast transport, which makes the conduction of H^- attractive. In this work, the H^- transport properties of BaH₂ have been investigated under pressure using in situ impedance spectroscopy measurements up to 11.2 GPa and density functional theoretical calculations. The H^- transport properties, including ionic migration resistance, relaxation frequency, and relative permittivity, change significantly with pressure around 2.3 GPa, which can be attributed to the structural phase transition of BaH₂. The ionic migration barrier energy of the P6₃/mmc phase decreases with pressure, which is responsible for the increased ionic conductivity. A huge dielectric constant at low frequencies is observed, which is related to the polarization of the H^- dipoles. The current study establishes general guidelines for developing high-energy storage and conversion devices based on hydride ion transportation.