Anion ordering enables fast H^- conduction at low temperatures

Area of Science:

• Solid-state chemistry
• Materials science
• Energy storage

Background:

• Ionic conductors are crucial for energy devices, but achieving high conductivity at low temperatures remains a challenge.
• Hydride materials show potential for energy applications, yet require improved ionic conductivity below 300°C.
• Current strategies often involve chemical disorder to stabilize conductive phases.

Purpose of the Study:

• To investigate novel layered anion-ordered barium halides (Ba₂-δH₃-2δX) as potential high-performance ionic conductors.
• To explore the relationship between crystal structure, anion ordering, and ionic conductivity in hydride materials.
• To identify new pathways for enhancing hydrogen-ion (H⁻) conduction at lower temperatures.

Main Methods:

• Synthesis and characterization of layered anion-ordered Ba₂-δH₃-2δX (X = Cl, Br, I) compounds.
• Ionic conductivity measurements across a range of temperatures.
• Analysis of crystal structure and defect chemistry, including Schottky defects and anion ordering.

Main Results:

• Ba₂-δH₃-2δX compounds exhibit remarkable ionic conductivity, reaching 1 mS cm⁻¹ at 200°C.
• Low activation barriers facilitate H⁻ conduction even at room temperature.
• Layered anion order and Schottky defects in Ba₂-δH₃-2δX suppress structural transitions, maintaining a hexagonal lattice.

Conclusions:

• Layered anion order, rather than chemical disorder, is an effective strategy for stabilizing conductive phases in hydride ionic conductors.
• These findings open new avenues for hydrogen-based electrochemical applications and energy devices.
• The developed materials offer a promising alternative for efficient ionic conduction at lower temperatures.