Single Ni atom doped WS2 monolayer as sensing substrate for dissolved gases in transformer oil: A first-principles study

Insulation defects and equipment failure often exist in power transformer, and insulating oil in transformer will experience decomposition with a series reaction. By detecting the dissolved gases in insulating oil, the operation status of transformer can be evaluated. In this study, the adsorption and gas sensing of several kinds of typical dissolved gas molecule (H2, C2H2, and CO) on pristine and single Ni atom doped WS2 monolayer (Ni-WS2) was theoretically investigated based on first-principles density functional theory. To discuss the adsorption behavior, the structures, adsorption energies, and electron transfers were calculated and compared. As to the electronic properties and chemical interactions between gas molecule and Ni-WS2, the band structures, density of states (DOS), and work functions were studied. The results show that, after the doping of Ni, the adsorption energies of H2, C2H2 and CO on WS2 monolayer increase dramatically, from −0.06 eV to −0.52 eV, −0.23 eV to −1.44 eV, and −0.15 eV to −1.68 eV, respectively. On Ni-WS2, H2 and C2H2 lose electrons while CO shows little electron transfer. Only the adsorption of C2H2 obviously reduces the band gap of Ni-WS2. For all three kinds of gas adsorption, hybridization of states between Ni 3d and atomic orbitals in molecule can be observed in DOS, indicating considerable chemical interactions. In addition, the adsorption of CO increases the work function of Ni-WS2 from 5.56 eV to 5.80 eV. Based on the change of different physical and chemical properties, the Ni-WS2 as sensing material in different gas sensors was evaluated and the desorption time was compared in order to shed light on the experimental realization to detect dissolved gas molecule in insulating oil with high sensitivity and selectivity.