Influence of near-surface oxide layers on TiFe hydrogenation: mechanistic insights and implications for hydrogen storage applications

18 May 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The inevitable formation of passivating oxide films on the surface of the TiFe intermetallic compound limits its performance as a stationary hydrogen storage material. Extensive experimental efforts have been dedicated to the activation of TiFe, i.e. oxide layer removal prior to utilization for hydrogen storage. However, development of an efficient activation protocol necessitates a fundamental understanding of the composition and structure of the air-exposed surface and its interaction with hydrogen, which currently is absent. Therefore, in this study we explored the growth and nature of the oxide films on the most exposed TiFe surface (110) in depth using static and dynamic first-principles methods. We identified the lowest energy structures for six oxygen coverages up to approximately 1.12 nm of thickness with a global optimization method and studied the temperature effects and structural evolution of the oxide phases in detail via ab-initio molecular dynamics (AIMD). Based on structural similarity and coordination analysis, motifs for TiO2, TiFeO3 as well as Ti(FeO2)x (x = 2, 3 or 5) phases were identified. On evaluating the interaction of the oxidized surface with hydrogen, a minimal energy barrier of 0.172 eV was predicted for H2 dissociation while the H migration from the top of the oxidized surface to the bulk TiFe was limited by several high-lying energy barriers above 1.4 eV. Our mechanistic insights will prove themselves valuable for informed designs towards new activation methods of TiFe and related systems as hydrogen storage materials.


hydrogen storage
oxide layer

Supplementary materials

Supplementary information for Influence of near-surface oxide layers on TiFe hydrogenation: mechanistic insights and implications for hydrogen storage applications
Computational details on calculation of the surface formation energies, the basin-hopping approach and the generation of the surface phase diagram. Calculation of the equilibrium Wulff shape. Visualization and labelling of the surface sites. Side-view of the oxide-layer growth. Additional hydrogenation energetics (CI-NEB plots for Path 3) and H-binding energies at sites T1–T5. Results of AIMD calculations of the 3L-MO model with excess oxygen. Details on utilization of SOAP descriptors and RDF results.


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