Hydride Ion Conductors with Polyanionic Complex Anions.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Hydride ion (H⁻)-conducting solid-state materials are crucial for electrochemical energy systems like batteries and fuel cells.
• Challenges exist in diversifying anion systems due to the reactive nature of hydride ions, hindering optimal transport.
• Developing new anion systems is key for advancing hydride ion conductor design.

Purpose of the Study:

• To report novel perovskite-type hydride ion conductors utilizing polyanionic borohydride (BH₄⁻).
• To investigate the structural and conductive properties of Sr₁₋ₓNaₓLiH₃₋<0xE1><0xB5><0xA7>(BH₄)ᵧ.
• To explore the role of coexisting H⁻ and BH₄⁻ anions and H⁻ vacancies in enhancing ionic conductivity.

Main Methods:

• Synthesis and structural characterization of perovskite-type compounds Sr₁₋ₓNaₓLiH₃₋<0xE1><0xB5><0xA7>(BH₄)ᵧ.
• Analysis of hydride ion conductivity through impedance spectroscopy.
• Neutron powder diffraction to elucidate the interaction between anions and cations and conduction pathways.

Main Results:

• Single-phase hydride ion conductors with coexisting H⁻ and BH₄⁻ were stabilized in the cubic perovskite structure at low-x values.
• Incorporating H⁻ vacancies (increasing y) significantly enhanced disorder of H⁻ and BH₄⁻, boosting hydride ion conductivity by three orders of magnitude.
• Neutron diffraction revealed asymmetric interactions between BH₄⁻ and cations, facilitating conduction via weaker interaction pathways.

Conclusions:

• A high hydride ion conductivity exceeding 10⁻⁴ S cm⁻¹ at 100 °C was achieved in the developed perovskite-type materials.
• The coexistence of H⁻ and BH₄⁻ anions and the strategic introduction of H⁻ vacancies are effective strategies for enhancing hydride ion conductivity.
• Complex anions, such as borohydride, show promise as novel anion systems for advanced hydride ion conductors.