DFT assessment of KBeO3-xHx perovskites: Revealing ion substitution mechanisms for enhanced solid hydrogen storage

Abstract

The exhaustion of non-renewable fossil resources has intensified the demand for sustainable energy generation and storage. The environmentally beneficial substitute hydrogen has storage and transportation issues. KBeO_3-xH_x and other perovskites are now attractive options for solid hydrogen storage. The physical characteristics of KBeO_3-xH_x for storing hydrogen are investigated in this study using GGA-PBE functional, which is carried in the CASTEP software in conjunction with Density Functional Theory (DFT), at various hydrogen concentrations (x = 0, 0.6, 1.2, 1.8, 2.4, 3). According to the study, adding hydrogen to the pure material changes its lattice characteristics and cubic structure. Phonon dispersion curve confirms the dynamical stability of our fully H-doped KBeO_3-xH_x material. Every material that contains hydrogen satisfies Born's mechanical stability requirements in terms of both structural and thermodynamic stability. Pugh's and Poisson's ratios reveal brittle behaviour of the studied materials. Cauchy's pressure shows that the materials' brittleness or ductility changes with hydrogen concentration. As demonstrated by band structure and density of states investigations, the addition of hydrogen dramatically changes electronic states, lowering the band gap from 7.598 eV to 0 eV. This electronic alteration affects refractive index, absorbance, and dielectric function, among other optical characteristics. The material's potential for both effective hydrogen storage and optoelectronic applications is further evidenced by the gravimetric hydrogen storage capacity (Cwt%), which varies from 0.67 % to 5.86 %. Our findings indicate that KBeH₃ is a superior material for storing hydrogen.