First-Principles Insight into Pd-Doped ZnO Monolayers as a Promising Scavenger for Dissolved Gas Analysis in Transformer Oil

ZnO monolayers with desirable n-type semiconducting properties are full of potential for sensing applications. In this work, we investigate using first-principles theory the adsorption and sensing behaviors of Pd-doped ZnO (Pd-ZnO) monolayers with two typical dissolved gases, namely, H₂ and C₂H₂, to explore their sensing use for dissolved gas analysis in transformer oil. For Pd doping on the pristine ZnO monolayer, the T_O site is identified as the most stable configuration with an E _b of -1.44 eV. For the adsorption of H₂ and C₂H₂, chemisorption is determined given the large adsorption energy (E _ad) and formation of new bonds. Analyses of the charge density difference and density of state provide evidence of the strong binding force of Pd-H and Pd-C bonds, while band structure analysis provides the sensing mechanism of the Pd-ZnO monolayer as a resistance-type sensor for H₂ and C₂H₂ detection with high electrical responses. Also, analysis of the work function (WF) provides the possibility of selective detection of H₂ and C₂H₂ using a Pd-ZnO monolayer-based field-effect transistor sensor given the opposite changing trend of the WF after their adsorption. Our work may broaden the application of ZnO-based gas sensors for application in the field of electrical engineering.