The hydrogen storage capacities of 4d transition metals in various boron systems

Abstract

The hydrogen adsorption and storage properties of BxM2 (M = Y-Mo, RuAg, x = 5–8) have been researched in detail. In B5M2 systems, most of compounds can adsorb multiple H2 with high gravimetric density, and their maximum adsorption are energetically favorable under room temperature. The atom-centered density matrix propagation (ADMP) molecular dynamics simulations show that B5Y2, B5Zr2, B5Nb2, and B5Ru2 can adsorb 6–10 H2 within 1000 fs at 300 K, and their gravimetric density are still close to or even higher the target of US Department of Energy (DOE). However, in more than half of the B5M2 systems, some H2 tend to dissociate and bond atomically on transition atoms in the process of adsorption. With the increase of boron atoms, the dissociation of adsorbed H2 will decrease. In B7M2 and B8M2, all of the H2 are adsorbed in the molecular form. Due to reversible average adsorption energy, satisfactory gravimetric density, ambient operating condition, the B5Pd2, B6Pd2, B7Y2, B7Zr2, B7Pd2, and B8Y2 complexes are the most promising hydrogen storage materials.