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

Abstract

We present density functional theory calculations, with a correction for the long-range interactions, of the adsorption of hydrazine (N2H4) 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 lonepair of electrons located on the N atoms, forming either monodentate or bidentate bonds with the surface. The strength of N2H4 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 gauchebridge configuration (Eads = −1.43 eV), followed by adsorption on the (100) where it also binds in gauche-bridge configurations (Eads = −1.27 eV), and most weakly onto the most stable (111) surface via one N−Ni bond in a trans-atop configuration (Eads = −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 N2H4 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. Graphical abstractDFT calculations have been employed to unravel the fundamental aspects of the adsorption process of hydrazine at a range of nickel surfaces, predicting the adsorption conformations, adsorption energies, structural parameters and electronic properties.

Development Trends on Nickel‐Based Electrocatalysts for Direct Hydrazine Fuel Cells

“…The theoretical measurements suggested that the interaction between N 2 H 4 molecules and OH − ions was a mixture of direct chemical and electrostatic modes. The interaction of N 2 H 4 molecule with the Ni surfaces can be realized through a lone‐pair of electrons centered on N atoms, constructing either monodentate or bidentate bonding with the catalytic surface [88] . The configurations of adsorbed N 2 H 4 bounded to a low coordinate Ni atom with monodentate structure on the Ni 3 S 2 (110) surface have been examined by Liu and co‐workers [89] .…”

“…The surface structure and porous texture would also play an important role contributing to ion diffusion and interface contact. Further, incorporating conductive counterparts and/or heteroatoms can endow catalysts with large surface areas and numerous active sites, which may render better enhancements in electrochemical activity [88,116] …”

“…For example, Menkah et al. studied the adsorption properties of N 2 H 4 not only on Ni(100), (110) and (111) perfect surfaces but also at vacancies and adatoms [88] . Based on analyses, the N 2 H 4 displayed a good activity to bind with Ni surfaces via a lone‐pair of electrons of N atoms, forming either monodentate or bidentate bonds with the surface.…”

“…The interaction of N 2 H 4 molecule with the Ni surfaces can be realized through a lone-pair of electrons centered on N atoms, constructing either monodentate or bidentate bonding with the catalytic surface. [88] The configurations of adsorbed N 2 H 4 bounded to a low coordinate Ni atom with monodentate structure on the Ni 3 S 2 (110) surface have been examined by Liu and co-workers. [89] Analyses elucidated that N 2 H 4 molecules could occupy the Ni 3 S 2 (110) surface with a strong interaction and much lower adsorption energy.…”

“…Further, incorporating conductive counterparts and/or heteroatoms can endow catalysts with large surface areas and numerous active sites, which may render better enhancements in electrochemical activity. [88,116] Apart from the electronic and chemical composition properties stated above, there has been a serious debate of considering thermodynamic and kinetic requirements of catalytic materials as crucial features. First, theoretical calculations and experimental data supposed that higher surface coverage is a more rational scenario in describing N 2 H 4 adsorption mechanism over Ni catalysts, in which their activities are robustly associated with the relatively high barriers of NÀ N and NÀ H bonds of N 2 H 4 .…”