Stability and hydrogen storage potential of zirconium-based A₂ZrH₆ (A = Na, K) hydrides: a DFT and AIMD investigation

Perovskite-based materials offer considerable potential for efficient, stable and environmentally sustainable hydrogen storage technologies. In this work an inclusive density functional theory (DFT) investigation was conducted to evaluate the structural, mechanical, optoelectronic and thermodynamic features of A₂ZrH₆ (A = Na, K) perovskite hydrides. Structural analysis reveals the stable cubic Fm3̄m symmetry, supported by favorable tolerance factors (0.92-0.99) and negative formation energies endorsing thermodynamic stability. Ab initio molecular dynamics (AIMD) simulations assure thermal stability at 300 K without significant structural distortion. Na₂ZrH₆ and K₂ZrH₆ exhibit notable hydrogen storage characteristics, achieving 4.22 and 3.45 wt% capacities with desorption temperatures of 441.39 and 258.91 K respectively. Mechanical analysis confirms elastic and Born stability with Poisson's ratios of 0.14 (Na₂ZrH₆) and 0.25 (K₂ZrH₆) and B/G ratios of 1.06 and 1.66 indicating brittle behavior. Electronic structure calculations confirm the band gaps of 1.25 and 1.87 eV while optical investigations indicate the suitability of these hydrides for photovoltaic applications. These results highlight A₂ZrH₆ (A = Na, K) perovskite hydrides as viable and efficient materials for next-generation hydrogen storage and energy conversion systems.