Improving Hydride Conductivity in Layered Perovskites via Crystal Engineering

Abstract

Hydride ion conduction in layered perovskites is of great interest for sustainableenergy applications. In this report we study Ba 2 ScHO 3 , a recently synthesized oxyhydride with an unusual anion ordering, using a multifaceted density functional theory approach involving both transition state calculations and molecular dynamics simulations. Beyond simply identifying the key ion migration pathways, we perform detailed analysis of transition states and identify key interactions which drive trends in ionic mobility. Our key findings are that ionic mobility is, remarkably, independent of hydride-oxide disorder, the dominant migration pathway changes under pressure, and a reduction in A-site cation size accelerates hydride diffusion. Local structural flexibility along migration pathways is understood in terms of dimensionality and ionic size, and we thus identify crystal engineering principles for rational design of ion conductors.On the basis of our new insights into these materials, we predict that Sr 2 ScHO 3 will show improved conductivity over existing analogues.

Sequential Pressure-Induced B1–B2 Transitions in the Anion-Ordered Oxyhydride Ba2YHO3

“…Ba 2 ScHO 3 and Ba 2 YHO 3 (Figure v), both recently synthesized and studied by our groups, − are chemically simpler in that they have d 0 B cations, so their structural preferences are controlled by electrostatics. Oxide and hydride anions are distributed across the available sites in accordance with the principle that the most charged anion coordinates to the most charged cation, so O 2– coordinates to Sc/Y 3+ in the perovskite layer and H – coordinates to Ba 2+ in the rock salt layer.…”

“…As a result, there may be an intermediate region in which half of the unit cell adopts CsCl ordering, while the other half retains rock salt ordering. The primary motivation for studying these materials is their ability to act as hydride anion conductors, and a previous computational study has shown that the principal anion conduction mechanism in Ba 2 ScHO 3 changes under pressure, from an interstitial-mediated pathway to one involving vacancies via a “bottleneck” transition state that has been observed in other hydride conductors. , The identification of materials with new hydride ordering patterns is, therefore, an important step in the study of novel hydride-ion conductors.…”

Temperature Dependent Local Atomic Structure and Vibrational Dynamics of Barium Hydride and Calcium Hydride

“…Solid-state materials that exhibit pure ionic conduction are highly attractive for use in energy storage and conversion devices such as fuel cells and batteries. While ionic transport has been observed in many materials and exploited commercially for species such as H + , Na + , Li + , and O 2– , only a small number of examples of hydride ion (H – ) transport have been discovered, namely in metal hydrides and oxyhydrides. − …”

Hydride Conductivity in Nitride Hydrides

“…Our calculated activation barrier for hydride diffusion is lower than the measured barrier in LaHO, the most conductive oxyhydride known. Among hydride conductors studied to date, SLHN is relatively unique in that interstitial hydrogen (rather than the hydrogen vacancy) is the primary defect driving the hydride migration; another example is the oxyhydride Ba 2 ScHO 3 , , in which equal mobility for hydride vacancies and interstitials has been predicted. We also use our methodology to assess the energetics of oxygen incorporation, highlighting the need to protect the material from oxygen.…”