Advanced theoretical engineering of KM₃H₉ (M = Fe, Co, Ni, Cu) hydrides for novel applications in hydrogen storage

Here, we propose a systematic first-principles study of K-based perovskite hydrides KM₃H₉ (M = Fe/Co/Ni/Cu) in the framework of density functional theory. The calculated formation energies indicate the thermodynamic stability of all the studied compounds, which is further confirmed by the absence of imaginary frequencies in the phonon dispersion spectra. The electronic structure analysis shows metallic nature for all the systems, and the magnetic computations show that the compounds have a stable antiferromagnetic ground state. The mechanical properties, particularly elastic constants, indicate that the materials are mechanically stable and have ductile behavior. Moreover, the thermodynamic analysis verifies the stability across a wide range of temperatures. Significantly, the hydrogen storage performance is studied, indicating that these materials have potential gravimetric and volumetric hydrogen storage capacities as well as suitable desorption temperatures. These results show the potential of KM₃H₉ (M = Fe/Co/Ni/Cu) hydrides as promising candidates for solid state hydrogen storage applications.