Hydrogen storage, optoelectronic, and structural properties of novel osmium hydrides

In present study, the density functional theory (DFT) is employed to analyze the structural, electronic, optical, and hydrogen storage characteristics of double perovskite-type hydrides A₂OsH₆ (A = Mg-Ba). The reported findings related to the structural aspects are in good agreement with the experimental results. All these compounds exhibit the FCC structure and formation enthalpy H_f which demonstrate their thermodynamic stability. The estimated band gap values for these compounds are 3.4, 3.0, 2.43, and 1.86 eV respectively by using perovskite-modified Becke-Johnson potential (P-mBJ) plus U parameter. According to the results, as going from Mg to Ba, the band gap decreases because of the increase in atomic radii. Furthermore, all the understudy compounds hold direct band gap nature, and their tuned band gap values show significant agreement with available results on isotropic compounds. The Mg₂OsH₆ is ultraviolet sensitive, and Ca₂OsH₆, Sr₂OsH₆, and Ba₂OsH₆ possess excellent optical behavior in the visible region. The characteristic dielectric function, oscillator strength, energy loss function, excitation coefficient, refractive index, reflectivity, and optical conductivity of these double perovskites type hydride indicate that they are highly suitable for optoelectronic applications. However, in terms of hydrogen storage performance, the gravimetric storage capacity of Mg₂OsH₆ is 2.77 wt%, for Ca₂OsH₆ is 2.59 wt%, for Sr₂OsH₆ is 2.15 wt%, and for Ba₂OsH₆ is 1.22 wt% while the favorable desorption temperature for these compounds is 189.46, 220.76, 311.19, and 356.37 K respectively with the formation energy of 24.76, 28.85, 40.67, and 46.58 kJ/mol, which is feasible in actual application.

In the current investigation, the FP-LAPW method is used which is executed in WEIN2k simulation code. The generalized gradient approximation and mBJ with Hubbard U are used to address the exchange and correlation potentials. The Kramar-Kroning relation is used for optical properties assessment. The analytical technique is used to find out the gravimetric hydrogen storage capacity for these compounds while all the plotting was performed using Xmgrace and Origen software.