The potential of hydrogen as an energy source has turned hydrogen storage into among the most extensively researched areas in the past few years. Here, the structural, electronic, elastic, optical, phonon, and thermodynamic properties of tetragonal Q2FeH5 (Q = Mg, Ca, Sr) hydrogen storage materials were comprehensively investigated through ab-initio calculations. The stable phonon dispersion spectra, coupled with the analysis of formation enthalpy, confirms the dynamic and structural stability of the hydrides under investigation. The electronic properties were calculated utilizing the Generalized Gradient Approximation (GGA) and the Trans-Blaha modified Becke-Johnson (TB-mBJ) approaches, revealing each of the three compounds – Mg2FeH5, Ca2FeH5, and Sr2FeH5 – display metallic characteristics. The mechanical properties of these compounds were also analyzed, as they must satisfy the Born – Huang criterion to ensure mechanical stability. The Cauchy pressure, Poisson's ratio and Pugh criteria indicated these compounds exhibit a brittle nature while being relatively rigid. At low energy levels, all the optical attributes were observed to be optimal to meet hydrogen storage needs. The gravimetric hydrogen storage capacities were determined to be 4.61 wt%, 3.57 wt%, and 2.13 wt% for Mg2FeH5, Ca2FeH5, and Sr2FeH5, respectively. It was observed that the gravimetric density rises as the cationic size diminishes, following the order Mg, Ca, and Sr. Furthermore, Mg2FeH5 was calculated to have the highest potential among the materials studied, making it particularly suitable for various renewable energy uses and sustained hydrogen fuel storage. 

Title

International Journal of Hydrogen Energy

Publisher

ELSEVIER

Publisher Country

United Kingdom

Indexing

Thomson Reuters

Impact Factor

8.1

Publication Type

Both (Printed and Online)

Volume

102

Year

2025

Pages

12