Density functional theory study of dissociative adsorption of H₂ molecules on NiTi (001) surfaces

Ti-based alloys have the potential to be used as hydrogen storage units, including NiTi. In contrast, NiTi alloy is sensitive to H atoms. It has been found that hydrogen can cause embrittlement in NiTi alloys. Thus, it is become indispensable to elucidate the reaction of H₂ molecules on the NiTi surface. Using density functional theory, we investigated the dissociation mechanism of H₂ molecules on the B2 NiTi (001) surface. We found that H atoms tend to come closer to Ni atoms on the Ti- and Ni-terminated (NiTi) (001) substrate. The calculation results showed that the adsorption energy of H atoms at the hollow site was higher than that at the top site. We identified two dissociation mechanisms of H₂ molecules on Ti and Ni terminated on NiTi (001) substrates via the hollow sites of the adsorption route. The adsorption energy values obtained were extremely low, that is, 0.23 and 0.38 eV for the Ni and Ti terminated of NiTi (001) substrates, respectively. The dissociation reaction of H₂ molecules, which is an exothermic reaction, can quickly occur on the NiTi (001) surface because of the low activation energy.