First-principles investigation on the physical and hydrogen storage properties of copper-based double perovskites A2CuH6 (A=Li, Na, K) for hydrogen storage applications

Abstract

Based on density functional theory, the structure, mechanical, optoelectronic, kinetic, thermodynamic and hydrogen storage properties of cubic A₂CuH₆ (A=Li, Na, K) double perovskites are studied. The lattice constants of Li₂CuH₆, Na₂CuH₆, and K₂CuH₆ are 6.32, 7.07, and 7.98 Å, respectively. The B/G values indicate that Li₂CuH₆ and K₂CuH₆ exhibit ductility, while Na₂CuH₆ exhibits brittleness. Electronic properties reveal that A₂CuH₆ (A=Li, Na, K) compounds have metallic nature. The optical properties of A₂CuH₆ show that Li₂CuH₆ and K₂CuH₆ crystals have high dielectric constants, which is beneficial for their applications as hydrogen storage. Importantly, A₂CuH₆ (A=Li, Na, K) materials were confirmed for their structural, dynamic, thermodynamic, and mechanical stability. Gravimetric hydrogen densities (GHD) of Li₂CuH₆, Na₂CuH₆, and K₂CuH₆ are 7.25, 5.23, and 4.09 wt%, respectively. The volumetric hydrogen storage capacities of Li₂CuH₆, Na₂CuH₆, and K₂CuH₆ are 159.06, 113.77, and 79.11 g·H₂/L, respectively. Therefore, Li₂CuH₆ owns the highest gravimetric and volumetric hydrogen storage capacities among these compounds. This study provides a new option for designing novel copper-based hydrogen storage materials.