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, H 2, CH 4, C 2 H 2, and C 2 H 4 ) in transformer oil adhere to HfSe 2 monolayers enhanced with metal oxides (ZnO, TiO 2 ). The results demonstrate that the pristine HfSe 2 monolayer exhibits weak physisorption for all five gases, characterized by small adsorption energies and long adsorption distances. Upon modification with ZnO and TiO 2, the adsorption performance improves significantly, particularly for CO, C 2 H 2, and C 2 H 4 . 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-HfSe 2 demonstrates superior gas sensing potential compared to that of TiO 2 –HfSe 2 . The adsorption capacity follows the order C 2 H 4 > C 2 H 2 > CO > CH 4 > H 2 for ZnO-HfSe 2 and C 2 H 2 > C 2 H 4 > CO > CH 4 > H 2 for TiO 2 –HfSe 2 . Analysis of the electronic properties reveals that ZnO modification enhances electrical conductivity, while TiO 2 modification reduces it. Recovery time analysis suggests that both modified materials are unsuitable for H 2 and CH 4 detection due to their extremely short recovery times. However, they are promising candidates for CO, C 2 H 2, and C 2 H 4 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 HfSe 2 to identify dissolved gases present in transformer oil.