A theoretical insight into hydrogen storage and thermoelectric properties of double perovskite hydrides Rb2CuYH6 and Cs2CuYH6

Abstract

Identifying promising double perovskite (DPs) hydride materials for efficient hydrogen storage is an important issue for hydrogen-based energy scenarios. Herein, we examine the structural, hydrogen storage, electronic, mechanical, optical, and thermoelectric properties of novel DPs hydrides Rb2CuYH6 and Cs2CuYH6 by using density functional theory. Structural studies revealed a cubic structure having space group 225 (Fm3m) with optimized lattice parameters of 8.70 Å for Rb2CuYH6 and 8.68 Å for Cs2CuYH6. Both compounds exhibit negative formation energies. For hydrogen storage applications, the estimated gravimetric capacities are 1.64 wt% for Rb2CuYH6 and 2.02 wt% for Cs2CuYH6. Band structure analysis revealed that both materials are indirect band gap semiconductors, with band gaps of 1.81 eV and 1.78 eV for Rb2CuYH6 and Cs2CuYH6, respectively. Both hydrides are found to have good mechanical properties, with a ductile nature and ionic bonding character. They also exhibit good thermoelectric properties, having ZT values of around 0.78 at 800 K. Our findings widen the scope for further exploration of other perovskite hydride materials, particularly for improved hydrogen storage capacity and for better design and experimental manufacturing of materials for effective hydrogen utilization. First-principles DFT predicts stable cubic Rb₂CuYH₆ and Cs₂CuYH₆ hydrides. Hydrogen-storage capacities reach 1.64 wt% and 2.02 wt%, respectively. Both hydrides are ductile ionic semiconductors with indirect band gaps. The materials exhibit a strong optical response in the ultraviolet region. Positive Seebeck coefficients indicate promising thermoelectric performance. First-principles DFT predicts stable cubic Rb₂CuYH₆ and Cs₂CuYH₆ hydrides. Hydrogen-storage capacities reach 1.64 wt% and 2.02 wt%, respectively. Both hydrides are ductile ionic semiconductors with indirect band gaps. The materials exhibit a strong optical response in the ultraviolet region. Positive Seebeck coefficients indicate promising thermoelectric performance.