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 A2SnH6 (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% (Li2SnH6) to 3.54 wt% (Na2SnH6) to 2.97 wt% (K2SnH6). 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 B0/G are Li2SnH6 = 4.31, Na2SnH6 = 2.59, and K2SnH6 = 1.94, confirming their ductile nature. Furthermore, Na2SnH6 exhibits the highest thermoelectric figure of merit (ZT = 0.79). While Li2SnH6 provides the highest gravimetric hydrogen capacity, Na2SnH6 exhibits the lowest predicted desorption temperature (311.07 K), compared with 337.36 K for K2SnH6. Overall, Na2SnH6 emerges as the most promising candidate for meeting the U.S. DOE hydrogen storage targets.