Publication Date

3-4-2026

Document Type

Article

Publication Title

Journal of Materials Chemistry A

Volume

14

Issue

23

DOI

10.1039/d5ta09720g

First Page

14445

Last Page

14453

Abstract

Sillén oxyhalides have recently emerged as promising materials for both photocatalytic and ionic transport applications, yet the role of likely-ubiquitous hydrogen-related defects in these layered compounds remains largely unexplored. Here, we employ first-principles defect calculations to investigate incorporation energetics for hydrogen- and oxygen-related defects, as well as their migration barriers in LaBi2O4X (X = Cl, Br, I) phases. We find that hydrogen interstitials, particularly protonic species (Hi+), are readily accommodated within the open Bi–O layers. Protons compete with oxygen vacancy donors (VO2+) and charge-compensate with oxygen interstitial acceptors (Oi2−). By linking hydrogen defect formation to water- and oxygen-related redox equilibria, we reveal that VO2+ facilitates Hi+ incorporation, while Oi2− promotes interstitial hydroxide formation, establishing a direct connection between proton and oxide-ion transport. Calculated migration barriers indicate that ionic diffusion is confined to Bi–O layers with low barriers of 0.20–0.25 eV for Hi+ and 0.14–0.25 eV for VO2+, suggesting that the materials contain intrinsic pathways for mixed ionic conduction. These results provide a microscopic picture of hydrogen behavior in Sillén oxyhalides and point to design strategies for integrating protonic and oxide-ion transport in layered oxyhalide electrolytes. Band-edge alignment analysis shows that LaBi2O4I provides the optimal combination of hydrogen solubility, oxygen defect stability, and mixed ionic conductivity, highlighting its potential for low-temperature electrochemical and energy-conversion applications. Overall, this work establishes the defect-driven origin of hydrogen transport in Sillén oxyhalides and expands their applicability beyond photocatalysis to mixed ionic conduction and hydrogen electrochemistry.

Funding Number

DE-AC52-07NA27344

Funding Sponsor

Office of Energy Efficiency and Renewable Energy

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Chemical and Materials Engineering

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