Density functional theory study of hydrogen and oxygen reactions on NiO(100) and Ce doped NiO(100)

Abstract

Context

This study aims to reveal the reaction mechanisms of H₂ and O₂ on the NiO(100) and Ce-doped NiO(100) surfaces using the density functional theory (DFT) combined with the on-site Coulomb correction (DFT + U) method. It was found that H₂ and O₂ react favorably on the reduced surfaces of both materials. However, after the oxygen vacancy is filled, the activation energy for the reaction between H₂ and lattice oxygen increases. Ce doping reduces this activation energy to 1.64 eV (compared to 3.16 eV for pure NiO(100)). The enhanced activity of lattice oxygen due to Ce doping is attributed to the charge transfer in the Ce–O bond, which leads to the electronic localization around O atoms and weakens the activation energy barrier. Moreover, the presence of Ce facilitates the formation of a sub-stable OH intermediate on the reduced surface, ensuring the sustainability of the reaction. This study provides a theoretical basis for the design of high-performance nickel-based hydrogen deoxidizers and contributes to promoting the research and development process of nickel-based catalysts in related fields.

Methods

The calculations were performed using the Vienna ab initio simulation package (VASP) module of the MedeA® software. The exchange–correlation energy calculations are performed using the Perdew, Burke and Ernzerhof (PBE) functional within the generalized gradient approximation (GGA). The transition states were calculated using the MedeA® Transition State Search Module, based on the climbing-image nudged elastic band (CI-NEB) method.