Strain boosts CO oxidation on Ni single-atom-catalyst supported by defective graphene

In order to realize the sulfur and water resistance and facilitate the CO oxidation reactions, the effects of strain on the adsorption of CO, O2, SO2 and H2O molecules on Ni single-atom-catalyst supported by single-carbon-vacancy graphene (Ni-SG) have been studied based on first principles calculations. It shows that the compressive strain increases the adsorption energies of all above mentioned molecules on Ni-SG, where SO2 is adsorbed more strongly on Ni-SG than CO. However, in the presence of tensile strain, the adsorption energies decreases significantly when the molecules (O2 and SO2) obtain electrons from Ni-SG, while the adsorption energies just slightly decrease when the molecules (CO and H2O) lose electrons to Ni-SG, which finally achieves the preferential adsorption of CO and O2 molecules on Ni-SG by tensile strain. In addition, with tensile strain increasing to 10%, the rate-limited energy barrier along Eley-Rideal (ER) path monotonically increases from 0.77 eV to 0.98 eV, while the rate-limited energy barrier along Langmuir-Hinshelwood (LH) path monotonically decreases from 0.54 eV to 0.44 eV, indicating that the tensile strain can facilitate the LH mechanism while imped the ER mechanism on Ni-SG. The Hirshfeld charge and orbital levels of O2 and CO molecules are modulated by the tensile strain, which plays an important role for the decreasing of energy barriers for CO oxidation. Overall, the tensile strain can enhance the sulfur and water resistance of Ni-SG, as well as boost the CO oxidation reactions.