Excellent hydrogen storage capabilities and optoelectronic attributes of XClH₆ (Li, Na, and K) perovskite hydrides for green energy technologies

The high hydrogen storage capacity, stability, and reversibility of perovskite hydrides make them promising materials for the energy industry. They play a vital role in sustainable energy technologies, including fuel cells and hydrogen storage systems. This work offers a comprehensive understanding of the physical attributes of XClH₆ (X = Li, Na, and K), utilizing the DFT-based Wien2K code. The quantum mechanical effects, along with Coulombic repulsions, are incorporated using the mBJ functional. For the assessment of the structural and thermo-dynamical integrity of XClH₆ (X = Li, Na, and K), optimization curves, tolerance factors, and formation energies are evaluated. The second ordered stress energy tensor is employed to compute the elastic constants of cubic XClH₆ (X = Li, Na, and K). The electronic properties are analyzed, which revealed indirect bandgaps of 0.29 eV, 0.55 eV, and 1.87 eV for LiClH_6, NaClH_6, and KClH₆, respectively. The electromagnetic interaction depicts that the studied hydrides possess higher divergence and dispersion in the visible range. The gravimetric densities for LiClH₆, NaClH₆, and KClH₆ are obtained as 10.97 wt%, 8.38 wt%, and 6.92 wt%, respectively, which exceed the criteria mentioned by the US DOE for 2025, making these materials excellent contenders for renewable energy and hydrogen storage.