Strontium Hydrides for Hydrogen Storage and Strain-Enhanced Hydrogen Desorption near Room Temperature

Metal hydrides are promising candidates for hydrogen storage due to their high volumetric hydrogen density. In this study, Sr₂H₄, a strontium-based hydride, is investigated using first-principles density functional theory (DFT) within the PBEsol generalized gradient approximation as implemented in CASTEP. The optimized structure exhibits a trigonal crystal system with lattice parameters a = b = 4.07 Å and c = 5.53 Å. Its negative formation energy confirms thermodynamic stability, while the absence of imaginary phonon modes indicates dynamical stability, mechanical stability is also ensured through the satisfaction of Born stability criteria. Electronic structure calculations reveal that Sr₂H₄ is a semiconductor with an indirect band gap of 1.109 eV, and optical analysis demonstrates favorable absorption and refractive properties, highlighting its potential for optoelectronic applications. From a hydrogen storage perspective, Sr₂H₄ shows a relatively high desorption temperature (~1008 K), a gravimetric capacity of 2.25 wt%, and a volumetric hydrogen density that meets U.S. Department of Energy targets. To improve its performance, strain engineering is applied, and the results indicate that compressive strain effectively weakens the Sr–H bonds and significantly reduces the desorption temperature, enabling hydrogen release near room temperature. These findings provide valuable insights into the design of efficient hydrogen storage materials and highlight the role of strain engineering as a practical strategy to optimize their performance under near-ambient conditions.