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Document Type

Original Article

Abstract

This study employs density functional theory (DFT) to investigate the fluorite-derived tetragonal hydride MgTiH4, highlighting its multifunctionality for energy-related applications. Structural optimization reveals lattice constants of a = b = 3.15 Å and c = 4.70 Å, with a unit cell volume of 46.59 Å3 and a high bulk modulus of 114.21 GPa, indicating mechanical robustness. Compared to its MgTiH4 and CaTiH4 analogs, SrTiH4 exhibits the highest phonon frequency (1355.19 cm-1). Superior thermodynamic stability (formation enthalpy: –3.35 eV) is seen in MgTiH4. Electronic band structure analysis reveals a narrow indirect band gap of 0.089 eV, suggesting semiconducting behavior with potential for low-light optoelectronics. Photocatalytic assessment indicates that the conduction band minimum of MgTiH4 lies at −1.837 V vs NHE and the valence band maximum at −1.748 V vs NHE. While the highly negative CBM provides a strong driving force for hydrogen evolution, the VBM is far below the water oxidation potential (+1.23 V), precluding spontaneous overall water splitting. The extremely small band gap further limits visible-light activation, suggesting these compounds are more suitable as hydrogen evolution-active materials rather than full water-splitting photocatalysts. Optical studies highlight strong IR absorption (up to 2.92 × 105 cm-1), high refractive index (7.81), and a pronounced dielectric constant (ε1 = 59.25), indicating excellent light-matter interaction. Gravimetric hydrogen storage capacity reaches 5.291 wt%, approaching DOE targets, while post-desorption studies confirm good structural reversibility and reduced bulk modulus (49.24 GPa), ensuring feasible hydrogen cycling. In conclusion, MgTiH4 outperforms CaTiH4 and SrTiH4 in multiple metrics, establishing it as a multifunctional candidate for future energy and photonic technologies.

Receive Date

31 Jan 2026

Revise Date

22 Mar 2026

Accept Date

02 June 2026

Publication Date

6-2-2026

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