Hydrogen storage properties of perovskite-type MgCoH₃ under strain effect

Abstract

In the present study, the crystal structure, phonon dispersion curves, stability, de/hydrogenation thermodynamic and kinetic properties of Perovskite MgCoH3 hydride under biaxial compression strain conditions were studied using the density functional theory (DFT) calculations. Our findings show that the biaxial strains played a key role in improving the de/absorption thermodynamic properties of MgCoH3 compound. Precisely, the formation energy shifted from −71.30 kJ mol−1 per H2 for unstrained MgCoH3 to −37.29 kJ mol−1 per H2 under the compression of −6% strain and the desorption temperature also decrease to 285.34 K compared with 545.52 K for free strained MgCoH3, which is close to optimum values for the practical application (289–393 K and −40 kJ mol−1 per H2). Noteworthy, the diffusion barrier energy of hydrogen atom in strained MgCoH3 is also calculated using the nudged elastic band method (NEB) and the obtained values decrease with the strain magnitude, which can accelerate the kinetic of hydrogenation process of MgCoH3. In addition, the band structures, phonon dispersion curves, the corresponding partial and total phonon density of states, also the thermal properties including the specific heat capacity, entropy and phonon free energy in terms of temperature with the variation of strain magnitude are predicted within the harmonic approximation. The analysis of phonons results revealed that crystal structure of MgCoH3 is dynamically and mechanically stable.