Substitution effects on the hydrogen storage behavior of AB2 alloys by first principles

Abstract

The hydrogen storage behavior of the TiCr 2 and ZrCr 2 alloys substituted with the third components (Zr, V, Fe, Ni) have been studied using first-principles calculations. The change of the hydrogen absorption energies caused by metal doping is arising from the charge transfer among the doped alloys interior. Zr and V atoms devoted abundant electrons, leading to a great enhancement of the H absorption energy, while Fe and Ni atoms always accepted electrons, yielding a remarkable decrease of the H absorption energy. The hydrogen diffusion energy barrier is closely correlated with the geometry effect rather than the electronic structure.

Substitutional effect of Ti-based AB2 hydrogen storage alloys: A density functional theory study

“…This is due to different charge transfer between hydrogen and metal atoms. Zr and V behave like electron donors, whereas Fe behaves like electron acceptors [26]. It was found in previous experiment that, the hydrogen capacity increases, hydrogen sorption plateau pressure decreases, absorption kinetics is accelerated, and desorption kinetics is decelerated due to the Zr substitution [27].…”

“…However, their performance on activation and high-rate dischargeability, is worse than C15 Laves phase (face-centred cubic structure) [24,25].In addition, hydrogenation enthalpy can be tuned by metal substitution. For example, the A-site substitution of Zr and Bsite substitution of V in TiCr 2 lead to the decrease of hydrogenation enthalpies, whereas B-site substitution of Fe shows opposite trend [26]. This is due to different charge transfer between hydrogen and metal atoms.…”

In situ NMR study of hydrogenation/dehydrogenation of ZrCr2 and physisorbed hydrogen

“…However, metallic systems are still quite promising to be developed into acceptable hydrogen storage media. An example of a metallic system, which has already been commercialized, is the intermetallic compound, LaNi 5 [12]. Although light metal-based systems such as MgH 2 show higher hydrogen storage capacities (on weight percent basis) [13], but due to ionic bonding between host atoms and H, their hydrides are quite stable and desorption is difficult.…”