Effect of Ni Doping and Vacancy Defects on the Sensing Characteristics of Graphene for NO<sub>2</sub> and CO Detection: A DFT Study

The sensing characteristics of pristine, Ni-doped, and C-vacancy graphene towards CO and NO 2 gas molecules were studied using density functional theory (DFT). The adsorption energies, electronic properties, charge transfer, and stable geometries were calculated to evaluate the gas-surface interaction mechanisms. Both pristine and vacancy graphene have smaller CO and NO 2 adsorption energies and charge transfer than the Ni-doped graphene, whereas the adsorption energy on Ni-doped vacancy graphene is higher than that of Ni-doped graphene. The results indicate that both CO and NO 2 gas molecules only attach to pristine graphene through weak physical adsorption. Stronger chemisorption occurs when the gas molecules adsorb on the surface of vacancy, Ni-doped, and Ni-doped vacancy graphene. Additionally, the results demonstrated that Ni-doped vacancy graphene has higher sensitivity and selectivity towards the NO 2 .