Pristine and Ni-doped WTe2 Monolayer for Adsorption and Sensing of C2H2 and C2H4 in Oil-Immersed Transformers: A DFT Study

Upon the adsorption and sensing of C2H2 and C2H4, we purpose pristine WTe2 monolayer as a promising candidate and uncover the enhanced mechanism of Ni-doping towards such two gas species in this work, using the density functional theory (DFT) method. Results show that pristine WTe2 monolayer performs physisorption upon C2H2 and C2H4 molecules with adsorption energies of -0.57 and -0.63 eV, and the small changes in its bandgap indicate the unsuitability for gas sensing use. The Ni-doping is energy-favorable with formation energy of -0.15 eV by substituting a Te atom on the WTe2 surface, and C2H2 and C2H4 adsorptions are both determined as chemisorption with adsorption energies of -1.40 and -1.22 eV. The electron redistributions are dramatically promoted in the Ni-WTe2/gas systems, and the obvious decrease of bandgap in Ni-WTe2 monolayer after C2H2 and C2H4 adsorptions, about 25.6% and 12.6%, suggests the strong potential for its exploration as a resistancetype gas sensor with sensing response of -97.8% and -85.4%. The analysis of recovery property reveals the reusability of Ni-WTe2 monolayer after several seconds exposure under UV light at 398 K. These findings give a deep insight into the WTe2-based gas sensor upon the typical gases in the transformer oil.