Structural, Electronic, Elastic and Hydrogen Storage Properties of Calcium Bis(tetrahydridoborate): A First-Principles Study

Abstract

First-principles calculations were carried out to study the electronic structure and mechanical and hydrogen storage properties of calcium bis(tetrahydridoborate) using density functional theory. The obtained equilibrium lattice parameters are in good agreement with the available experimental data. The stability of the structure at zero pressure is determined by the calculation of the elastic coefficients. Nevertheless, the existence of elastic anisotropy in the compound demonstrates its lower compressibility along the c-axis than the a- and b-axes. F2dd-Ca(BH4)2 is nonmetallic with a wide band gap of 5.54 eV. In this regard, Ca(BH4)2 is promising for hydrogen storage applications at the expense of its high hydrogen volume density of 130 g/L (more than that of liquid hydrogen) and a hydrogen gravimetric density of 11.46 wt%, exceeding the U.S. Department of Energy's 2025 goal of 5.5 wt%.