A precise prediction for the hydrogen storage ability of perovskite XPH3 (X=Li, Na, K) hydrides: First-principles study

Hydrogen storage remains a significant barrier to creating a sustainable hydrogen economy, as many current materials fail to meet the high safety, efficiency, and capacity requirements. Current hydrogen storage technologies frequently exhibit low gravimetric densities and slow absorption/desorption rates, which limit their practical applicability in energy systems. This manuscript reports the first principles analysis on the physical features of alkali-based perovskite hydrides LiPH3, NaPH3, and KPH3, along with their hydrogen storage potential. Volume optimization curves, negative formation enthalpies and tolerance factor manifested the complete structural and geometric stability of these studied hydrides. Brittle, higher resistance to indentation, endurance towards high temperatures and anisotropic behavior are revealed through mechanical attributes for LiPH3, NaPH3, and KPH3. Higher longitudinal velocities are observed in crystallographic planes. The directional velocities for XPH3 (X = Li, Na, K) reflect an anisotropic nature in each crystallographic plane. The electronic band structure, TDOS and PDOS elaborates the metallic behavior of these studied hydrides. These hydrides' optical characteristics showed that they have good optical conductivity in the UV spectrum, along with minimal polarization and dispersion in the UV region. The hydrogen storage capacities for LiPH3 (6.83 wt%), NaPH3 (5.00 wt%), and KPH3 (3.95 wt%) signifies that all perovskite hydrides have shown promising results for hydrogen storage but LiPH3 is the strongest contender for hydrogen storage with highest gravimetric ratio (6.83 wt%) and volumetric storage (93.39 gH2/L) as it fulfills the energy storage demand mentioned by US-DOE of metal hydrides for year 2025.