Adsorptive Characteristics of an HfSe 2 Monolayer Functionalized with Metal Oxides (ZnO, TiO 2 ) for Sensing Transformer-Oil-Dissolved Gases (CO, H 2 , CH 4 , C 2 H 2 , C 2 H 4 )

Utilizing density functional theory (DFT) computational techniques, this paper examines how dissolved gases (CO, H2, CH4, C2H2, and C2H4) in transformer oil adhere to HfSe2 monolayers enhanced with metal oxides (ZnO, TiO2). The results demonstrate that the pristine HfSe2 monolayer exhibits weak physisorption for all five gases, characterized by small adsorption energies and long adsorption distances. Upon modification with ZnO and TiO2, the adsorption performance improves significantly, particularly for CO, C2H2, and C2H4. These improvements are reflected in stronger adsorption energies, reduced adsorption distances, and increased charge transfer, indicating stronger interactions and, in some cases, chemisorption. Among the two modified systems, ZnO-HfSe2 demonstrates superior gas sensing potential compared to that of TiO2-HfSe2. The adsorption capacity follows the order C2H4 > C2H2 > CO > CH4 > H2 for ZnO-HfSe2 and C2H2 > C2H4 > CO > CH4 > H2 for TiO2-HfSe2. Analysis of the electronic properties reveals that ZnO modification enhances electrical conductivity, while TiO2 modification reduces it. Recovery time analysis suggests that both modified materials are unsuitable for H2 and CH4 detection due to their extremely short recovery times. However, they are promising candidates for CO, C2H2, and C2H4 sensing, with recovery times that can be optimized by adjusting the temperature. This study offers theoretical foundations for creating advanced gas sensors that utilize metal-oxide-modified HfSe2 to identify dissolved gases present in transformer oil.