SF6 insulation equipment is crucial for the reliable operation of power systems, with SF6 gas serving as the primary insulating medium. This gas plays a vital role in preventing insulation problems like partial discharge and overheating, thus ensuring optimal insulating efficiency [1]. Under partial discharge, electric arc, or thermal stress conditions, SF6 gas can undergo dissociation, producing reactive fragments such as SF4, SF2, and free fluorine atoms. These intermediates may further react with trace amounts of water vapor and oxygen within the gas-insulated system, resulting in stable secondary byproducts such as SO2, SOF2, and SO2F2. Additionally, H2S can be produced through reactions involving sulfur-containing species and hydrogen atoms originating from moisture or hydrocarbon contaminants [[2], [3], [4], [5], [6]]. These gaseous byproducts are commonly detected in malfunctioning or aged SF6-insulated equipment, and their presence is closely linked to insulation degradation [[7], [8], [9]]. Consequently, to maintain the safe and stable operation of gas-insulated switchgear (GIS), it has become crucial to implement precise online monitoring of SF6 decomposition products. Such monitoring is essential for maintaining the overall stability of power systems.

During the past few years, researchers are increasingly investigating nano-sensing technologies and exploring the 2D materials like C2N, C3N, h-BN, silicene, phosphorus, MXene, transition metal disulfides (TMD) and so on, as potential sensors [[10], [11], [12], [13], [14], [15], [16]]. These 2D layered materials share a structural similarity with graphene while addressing the lack of a band gap found in graphene. The ongoing advancements in two-dimensional materials have spurred a rise in gas detection research, especially for specific applications or in challenging environments [[17], [18], [19], [20], [21]]. Among these materials, TMDs, in particular, have garnered attention for their impressive sensing capabilities, quick response times, and simple synthesis methods [[22], [23], [24], [25]], making them highly suitable for the detection SF6 decomposition products in power systems. Many metal-doped TMDs have been modeled using density functional theory (DFT) to study their sensing performance [[26], [27], [28], [29]]. These studies indicate that metal doping can significantly improve the electronic structure and conductivity of TMDs, enhancing their selectivity and sensitivity to specific gases. Furthermore, the layered structure of TMDs allows for higher sensitivity and faster responses at the microscopic scale, promising effective solutions for fault diagnosis and early warning in electrical equipment.

Recently, the InSe monolayer has attracted considerable attention for research in optoelectronic properties, electronic devices and sensing properties, thanks to its exceptional electron mobility and carrier density [[30], [31], [32], [33]]. Moreover, InSe-based heterostructures, and even InSe flakes have demonstrated impressive catalytic performance in various experimental and theoretical studies [34,35]. However, as a gas sensing material, the pristine InSe monolayer exhibits limited chemical interactions with most common gas molecules, resulting in weak adsorption energies. This behavior restricts its effectiveness in gas detection applications. To enhance its sensing capabilities, researchers have explored various strategies, including the introduction of structural defects, such as vacancy defects and doping with different elements. For example, Zhang et al. studied the gas sensing properties of pristine and n-type InSe monolayers toward SF6 decomposition products by doping with fluorine (F) using density functional theory [36]. They found that fluorine doping significantly improved the chemical interaction with SO2, increasing adsorption energy and electron transfer. The InSe-F monolayer also demonstrated strong selectivity and favorable recovery characteristics for SO2, indicating its potential for gas detection. Additionally, metal doping can also modify the electronic properties of InSe, enhancing its chemical reactivity with gas molecules. For instance, doping InSe with metals such as Pt, Ag, Au, and Pd can enhance the adsorption strength of the InSe monolayer for CO2, subsequently increasing its sensitivity to CO2 [37]. Although various doped InSe systems have been investigated, the gas sensing potential of nickel-doped InSe (Ni-InSe) monolayers remains largely unexplored, presenting a valuable opportunity for further study. Motivated by this gap, we examine whether incorporating nickel into the InSe matrix can enhance its sensing performance. Nickel, known for its strong catalytic activity, may significantly strengthen the interaction between the Ni-InSe monolayer and gas molecules, particularly those derived from SF6 decomposition [38,39]. Using density functional theory, we systematically assess the structural stability, electronic properties, and adsorption behavior of Ni-InSe monolayer. This approach enables us to evaluate the impact of Ni doping on the electronic structure and chemical reactivity toward key decomposition gases, including H2S, SO2, SOF2, and SO2F2. Furthermore, the intrinsic layered structure of InSe may contribute to faster response times and improved detection sensitivity. Overall, this study aims to fill the current knowledge gap and establish Ni-InSe as a promising candidate for real-time monitoring of SF6 decompositions in gas-insulated switchgear (GIS) systems, advancing the development of efficient gas sensing technologies in power applications.