Lattice dynamic stability and hydrogen storage mechanism of Al3BH12 and Al2B2H12 under pressure: Ab initio study for hydrogen storage improvement

Abstract

Additional compositions with structural stabilities in a subset of the aluminum-boron hydrides (Al–B–H) under different pressures are theoretically investigated through the ab initio random structure searching method. The lattice dynamical stability of new stable compositions (Al3BH12 and Al2B2H12) is discovered and presented through the entirely positive modes of the phonon dispersion relation. We therefore observe the important parameters in the field of hydrogen storage, such as formation enthalpy, gravimetric hydrogen density, desorption temperature, band structure, and temperature dependence. We analyze the hydrogen storage mechanisms of three stable Al–B–H compounds, including Al3BH12, Al2B2H12, and AlB3H12, to compare the hydrogen release abilities and make recommendations for improving energy storage under the effect of pressure. Furthermore, the calculated activation curves from the hydrogen vacancy diffusion kinetics to the host hydrides indicate a high probability of hydrogen transport to these host hydride materials. The newly discovered compound Al2B2H12 (C2/m) has interesting potential for hydrogen storage due to its ability to both absorb and release hydrogen atoms from host materials.