Pressure-dependent DFT study of A2LuCuH6 (A = Li, Na, K) hydrides for hydrogen storage and photo-catalytic water splitting applications

Abstract

Next-generation clean-energy technologies seek efficient solid-state energy storage materials for hydrogen-based energy systems that exhibit thermodynamically stable properties and multifunctional optoelectronic performance. In the current article, the structural, hydrogen-storage, mechanical, electronic, optical, thermodynamic, and photocatalytic properties of the A 2 LuCuH 6 (A = Li, Na, K) cubic double perovskite hydrides are systematically investigated using first principles density functional theory calculations. The optimized lattice constant gradually rises from 7.78 Å in Li 2 LuCuH 6 to 7.94 Å in Na 2 LuCuH 6 and 8.18 Å in K 2 LuCuH 6 , and the bulk modulus gradually reduces from 43.48 to 39.29 GPa, showing gradually increasing lattice softening. Negative formation enthalpies of -43.08, -48.71, and − 54.99 kJ/mol verify their thermodynamic stability. The gravimetric hydrogen-storage capacities are recorded as 2.34, 2.08, and 1.87 wt%, while the volumetric capacities are 21.33, 20.06, and 18.35 gH 2 /L for Li, Na, and K-based compounds, respectively. The computed hydrogen desorption temperatures are 329.61, 372.54, and 420.73 K, which show tunable hydrogen-release behavior. The indirect semiconducting band gaps in the range of 1.46–2.01 eV at ambient pressure with strong optical absorption in the visible-UV range. In addition, the favorable band-edge alignment is indicative of photocatalytic suitability for overall water splitting, and the pressure-dependent thermodynamic parameters indicate lattice rigidity and a decrease in anharmonic effects under compression, which demonstrates the multi-functional energy potential of these hydride perovskites.