Selective detection of dissolved fault gases in on-load tap changer insulating oil using WO3−-Modified Janus HfSeTe: A First-Principles Study

Online monitoring of dissolved fault gases in on-load tap changer (OLTC) insulating oil is crucial for the reliable operation and condition assessment of power equipment. In this work, first-principles calculations were employed to systematically investigate the gas-sensing behavior of pristine Janus HfSeTe monolayers and WO 3 -modified HfSeTe toward typical dissolved fault gases, including H 2 , CO 2 , CH 4 , C 2 H 4 , and C 2 H 2 . The results show that pristine HfSeTe, irrespective of Se- or Te-terminated surfaces, exhibits weak physical adsorption for all investigated gases, accompanied by negligible charge transfer and minor electronic structure modulation, indicating limited intrinsic sensing capability. In contrast, WO 3 functionalization significantly enhances gas–substrate interactions and induces pronounced electronic responses toward unsaturated hydrocarbons. WO 3 –HfSeTe displays strong and selective adsorption for C 2 H 4 and C 2 H 2 , while remaining insensitive to H 2 , CO 2 , and CH 4 . Notably, C 2 H 4 adsorption results in a substantial band gap reduction of 32.49%, whereas C 2 H 2 adsorption is characterized by considerable charge transfer and deep electronic state reconstruction. Desorption kinetic analysis reveals that WO 3 –HfSeTe enables room-temperature operation for C 2 H 4 with a moderate desorption time of 69.8 s, and rapid recovery for C 2 H 2 can be achieved under mild thermal activation. Ab initio molecular dynamics (AIMD) simulations further confirm the thermal stability of the adsorption systems. These findings highlight the potential of WO 3 -modified Janus HfSeTe for selective online monitoring of key dissolved fault gases in OLTC insulating oil.