First-principles prediction of the physical properties of the Al-based hydride XAlH5 (X = Ca, Sr, Ba) for hydrogen storage applications

Abstract

To identify potential hydrogen storage materials, this study uses first-principles calculations to predict the thermodynamic, storage, mechanical, electronic, optical, and dynamic properties of aluminum-based hydride XAlH₅ (X = Ca, Sr, Ba). The negative formation enthalpy of XAlH₅ (X = Ca, Sr, Ba) hydrides, along with Born stability criteria and phonon dispersion analysis, indicates their thermodynamic, mechanical, and dynamic stability. Predictions for the B/G ratio and Poisson's ratio reveal that CaAlH₅ is ductile, whereas SrAlH₅ and BaAlH₅ are brittle materials. Electronic property predictions show that aluminum-based hydride XAlH₅ (X = Ca, Sr, Ba) are semiconductors. Bonding analysis reveals that CaAlH₅ contains only ionic bonds, while SrAlH₅ and BaAlH₅ include both covalent and ionic bonds. CaAlH₅, with the smallest band gap, facilitates electron transitions between the valence and conduction bands, making it ideal for hydrogen release. The predicted weight hydrogen storage capacities for XAlH₅ (X = Ca, Sr, Ba) hydrides are 6.99 wt% for CaAlH₅, 4.21 wt% for SrAlH₅, and 2.98 wt% for BaAlH₅, with hydrogen desorption temperatures of 277K, 297K, and 333K. Among the XAlH₅ (X = Ca, Sr, Ba) hydrides, CaAlH₅ demonstrates the best hydrogen storage potential and should be considered a promising material for future hydrogen storage applications.