Hydrazine adsorption on perfect and defective fcc nickel (100), (110) and (111) surfaces: A dispersion corrected DFT-D2 study

We present density functional theory calculations, with a correction for the long-range interactions, of the adsorption of hydrazine (N ₂ H ₄ ) on the Ni (110), (100), and (111) surfaces, both defect-free planes and surfaces containing point defects in the form of adatoms and vacancies. Several low-energy adsorption structures for hydrazine on the perfect and defective surfaces have been identified and compared. The hydrazine molecule is shown to interact with the Ni surfaces mainly through the lone-pair of electrons located on the N atoms, forming either monodentate or bidentate bonds with the surface. The strength of N ₂ H ₄ adsorption on the perfect surfaces is found to be directly related to their stability, i.e. it adsorbs most strongly onto the least stable (110) surface via both N atoms in a gauche-bridge configuration (E _ads = −1.43 eV), followed by adsorption on the (100) where it also binds in gauche-bridge configurations (E _ads = −1.27 eV), and most weakly onto the most stable (111) surface via one N–Ni bond in a trans-atop configuration (E _ads = −1.18 eV). The creation of defects in the form of Ni adatoms and vacancies provides lower-coordinated Ni sites, allowing stronger hydrazine adsorption. Analysis into the bonding nature of N ₂ H ₄ onto the Ni surfaces reveals that the adsorption is characterized by strong hybridization between the surface Ni d-states and the N p-orbitals, which is corroborated by electron density accumulation within the newly formed N–Ni bonding regions.