Comprehensive insights into the hydrogen storage, mechanical, structural, thermodynamic, electronic and optical properties of (Li/Na/K)PH6 for renewable energies

Abstract

The increasing interest in perovskite hydrides stems from their potential to serve as efficient, high-capacity hydrogen storage materials. This study presents a detailed investigation of the physical characteristics of XPH₆ (X = Li, Na, and K) performed utilizing the FP-LAPW method inside the framework of the Wien2K code. The structural and thermodynamic stability is evaluated using several factors. The GGA potential is used to assess the hydrides’ structural and mechanical characteristics. In contrast, the mBJ functional is used to investigate the electrical and optical properties of XPH₆ (X = Li, Na, K). Young's modulus, computed from the three independent elastic constants, reveals a decreasing trend with increasing atomic size of the hydrides. Furthermore, the brittle nature of these hydrides is confirmed via Pugh's ratio, Cauchy's pressure, and Poisson's ratio. The electronic study indicates indirect bandgaps of 4.66 eV, 5.54 eV, and 6.55 eV for LiPH₆, NaPH₆, and KPH₆, respectively, demonstrating that these hydrides have wide bandgaps. The elastic anisotropy for XPH₆ (X = Li, Na, K) is measured using ELATE software. An in-depth examination of the optical characteristics demonstrates that these perovskite hydrides have significant UV absorption, indicating their potential use in optoelectronic devices. Furthermore, the hydrogen storage capabilities for LiPH₆, NaPH₆, and KPH₆ are calculated to be 12.01 wt% (50.22 g_H2 per L), 9.08 wt% (47.89 g_H2 per L), and 7.31 wt% (43.96 g_H2 per L), respectively, making them appropriate for hydrogen storage purposes.