First-principles investigation of A2SnH6 (A = Li, Na, K) double perovskite hydrides for energy conversion applications

Abstract This study explores the solid-state hydrogen storage capacity of A 2 SnH 6 (A = Li, Na, K) double perovskite hydrides. The substitution of Li with Na and K leads to an increase in lattice parameters from 7.56 to 7.73 and 7.99 Å. The enthalpy of formation and AIMD computation confirm their thermodynamic and thermal stabilities. The gravimetric hydrogen storage capacities decrease from 4.36 wt% (Li 2 SnH 6 ) to 3.54 wt% (Na 2 SnH 6 ) to 2.97 wt% (K 2 SnH 6 ). All these configurations have wide indirect band gaps (2.74–3.12 eV), demonstrating their semiconducting nature, making them viable for UV photocatalytic water splitting. The calculated values of Pugh B 0 /G are Li 2 SnH 6 = 4.31, Na 2 SnH 6 = 2.59, and K 2 SnH 6 = 1.94, confirming their ductile nature. Furthermore, Na 2 SnH 6 exhibits the highest thermoelectric figure of merit (ZT = 0.79). While Li 2 SnH 6 provides the highest gravimetric hydrogen capacity, Na 2 SnH 6 exhibits the lowest predicted desorption temperature (311.07 K), compared with 337.36 K for K 2 SnH 6 . Overall, Na 2 SnH 6 emerges as the most promising candidate for meeting the U.S. DOE hydrogen storage targets.