Ir- and Pt-Doped InTe Monolayers as Potential Sensors for SF₆ Decomposition Products: A DFT Investigation

Abstract

The burgeoning demand for reliable fault detection in high-voltage power equipment necessitates advanced sensing materials capable of identifying trace sulfur hexafluoride SF₆ decomposition products (SDPs). In this work, the first-principles calculations were employed to comprehensively evaluate the potential of Ir- and Pt-doped InTe (Ir-InTe and Pt-InTe) monolayers as high-performance gas sensors for the four specific SDPs (H₂S, SO₂, SOF₂, SO₂F₂). The results reveal that Ir and Pt atoms are stably incorporated into the hollow sites of the InTe monolayer, significantly reducing the intrinsic bandgap from 1.536 eV to 0.278 eV (Ir-InTe) and 0.593 eV (Pt-InTe), thereby enhancing the material’s conductivity. Furthermore, Ir-InTe exhibits selective chemisorption for H₂S, SO₂, and SOF₂, with adsorption energies exceeding −1.35 eV, while Pt-InTe shows chemisorption capability for all four SDPs. These interactions are further supported by significant charge transfer and orbital hybridization. Crucially, these interactions induce notable bandgap changes, with Ir-InTe showing up to a 65.5% increase (for SOF₂) and Pt-InTe showing an exceptional 105.2% increase (for SO₂F₂), alongside notable work function variations. Furthermore, recovery time analysis indicates that Ir-InTe is suitable for reusable H₂S sensing at 598 K (0.24 s), whereas Pt-InTe offers recyclable detection of SO₂ (5.27 s) and SOF₂ (0.16 s) at the same temperature. This work provides theoretical guidance for the development of next-generation InTe-based gas sensors for the fault diagnosis in high-voltage power equipment.

1. Introduction

Sulfur hexafluoride (SF₆), as an excellent gas insulation medium owing to its superior dielectric strength and arc quenching capabilities, is extensively used in high-voltage power equipment (HVPE), including circuit breakers, switchgear, and gas-insulated substations [1,2]. However, under some extreme conditions such as high electric fields and partial discharges, SF₆ inevitably decomposes into a series of toxic byproducts (H₂S, SO₂, SOF₂, and SO₂F₂) [3,4]. These SF₆ decomposition products (SDPs) can accelerate the aging and degradation of insulating materials, potentially leading to a decline in the insulation performance of high-voltage electrical equipment and ultimately causing failure or catastrophic breakdown [5,6]. Fortunately, these SDPs can serve as early indicators of incipient faults within the equipment [7]. To enable early warning and online monitoring of SDPs, researchers have actively pursued the development of high-performance gas sensing materials. However, despite the application of online monitoring technologies such as semiconductor metal oxide sensors [8], they face significant challenges, including insufficient sensitivity, poor selectivity, and relatively high operating temperatures [9]. Particularly in complex field environments, achieving highly selective detection of trace SDPs remains a significant and unresolved challenge.

In recent years, two-dimensional (2D) materials have demonstrated unparalleled advantages in gas sensing due to their enormous specific surface area, abundant surface active sites, and tunable electronic structures [10]. Various types of 2D materials have been extensively investigated for detecting SDPs [11,12]. For instance, graphene and its functionalized derivatives exhibit excellent adsorption and response capabilities towards gases such as SO₂ and H₂S, attributed to their high conductivity and introduced surface functional groups [13,14]. Transition metal dichalcogenides (TMDs), including MoSe₂ and SnS₂, have proven effective in adsorbing and detecting specific SDPs through modulation of their electronic structures and defect states [15]. Emerging 2D materials, such as MXenes [16,17], 2D oxides [18], nitrides [12,19], and GeSe monolayer [20], have also demonstrated sensitivity to particular SDPs. Recent theoretical works continue to validate the DFT approach by screening novel materials, such as Ag-doped graphdiyne, for their potential in SDP sensing [21]. Currently, indium ditelluride (InTe), a novel 2D semiconductor with an appropriate bandgap and distinctive structural characteristics, offers a promising platform for constructing next-generation sensors. However, pristine InTe monolayers predominantly exhibit weak physical adsorption towards SDPs [22]. Such feeble interactions typically result in low adsorption energies and minimal charge transfer [23], which fail to induce significant changes in the electrical signals of the substrate material. Consequently, these limitations restrict the sensitivity and recovery speed of InTe-based gas sensors, hindering their ability to meet practical requirements for rapid and precise detection of trace SDPs.

To address the inherent limitations of pristine InTe monolayers, surface modification, particularly the introduction of metal atom doping, offers an effective strategy to alter the material’s local electronic structure and surface activity. Extensive research has confirmed that single-metal atom doping can significantly enhance the adsorption capacity and sensing response of various two-dimensional materials, such as graphene [13], MoS₂ [6], BN [24], and InN [25], towards SDPs. For example, doping with noble metals like Pt, Pd, and Au can leverage their unique electronic structures and catalytic activities to significantly enhance the gas sensitivity of 2D materials towards target gases [2,3,26,27]. Similarly, doping with transition metals such as Fe, Co, and Ni may facilitate stronger coordination or chemical bonding through interactions between their d-orbitals and the p-orbitals or π bonds of gas molecules [4], consequently increasing adsorption energy and charge transfer efficiency [28]. Considering Ir and Pt as representative transition and noble metals, respectively, they possess unique d-orbital electron configurations and catalytic activities. These characteristics are anticipated to significantly enhance the adsorption capacity of the InTe monolayer towards SDPs by modifying its local electronic structure.

Here, first-principles calculations are employed to systematically investigate the adsorption behaviors and sensing properties of Ir- and Pt-modified InTe (denoted as Ir-InTe and Pt-InTe) monolayers towards four typical SDPs (H₂S, SO₂, SOF₂, SO₂F₂). The stability of the doped InTe monolayers are first assessed by evaluating their binding energies and electronic structures. Subsequently, the optimal adsorption configurations are identified by comparing the adsorption energies of the SDPs on both Ir-InTe and Pt-InTe surfaces. The microscopic interaction mechanisms between the target gases and the substrates are elucidated through analyses of the electronic properties, including projected density of states, charge density distribution, and differential charge density. Furthermore, the bandgap, work function, and recovery time are calculated for each adsorption system to theoretically assess the feasibility of Ir-InTe and Pt-InTe monolayers as SDP sensors and to explore their potential sensing mechanisms. This work provides important theoretical guidance for the design and development of novel high-performance InTe-based gas sensors, and the proposed sensors may reduce emissions of SF₆, a potent greenhouse gas, by reducing equipment failures. This paper is organized as follows: Section 2 details the computational methods employed in this study. Section 3 presents and discusses the results regarding the material properties and gas sensing performance. Finally, Section 4 summarizes the key findings and conclusions of our investigation.

2. Computational Details

All theoretical calculations were performed using the DMol³ module of the Materials Studio 2020 software package (Dassault Systèmes BIOVIA, San Diego, CA, USA) [29]. The exchange-correlation functional was described by the Peered–Burke–Ernzerhof (PBE) functional within the generalized gradient approximation (GGA) [30,31], and van der Waals interactions were included using the Tkatchenko–Scheffler (TS) method [32]. Electron–ion interactions were modeled using DFT semi-core pseudopotentials (DSPP), which explicitly treated the valence and semi-core electrons [33]. Valence electron wave functions were expanded using the high-precision double numerical plus polarization (DNP) basis set [34], with a cutoff radius of 5.0 Å. A 4 × 4 × 1 supercell model of single-layer InTe was constructed, incorporating a 20 Å vacuum layer perpendicular to the monolayer to eliminate spurious interactions between periodic images. Brillouin zone integration was performed using the Monkhorst–Pack method [35]. A 5 × 5 × 1 K-point mesh was employed for geometric optimization, while a denser 10 × 10 × 1 mesh was used for calculating electronic properties. Convergence criteria for geometry optimizations were set as follows: total energy change < 1.0 × 10⁻⁵ Ha, maximum force on each atom < 0.002 Ha/Å, and maximum atomic displacement < 0.005 Å. Self-consistent field (SCF) calculations were considered converged when the total energy change was less than 1.0 × 10⁻⁶ Ha.

The binding energy (E_bin) was computed in order to assess the post-modification structural stability of Ir-InTe and Pt-InTe monolayers [36]:

$$E_{\mathrm{bin}}=E_{\mathit{TM}-\mathit{InTe}}-E_{\mathit{InTe}}-E_{\mathit{TM}}$$

(1)

Transition metal (TM)-modified InTe, pristine InTe, and an isolated TM atom are denoted by the symbols $E_{\mathit{TM}-\mathit{InTe}}$, $E_{\mathit{InTe}}$, and $E_{\mathit{TM}}$ respectively, along with their corresponding total energies. According to recognized DFT benchmarks, E_bin values larger than −3.0 eV indicate thermodynamically stable doping. Additionally, the adsorption affinity of TM-InTe monolayers for gas molecules was assessed using the adsorption energy (E_ads), which is defined as [37]:

$$E_{\mathrm{ads}}=E_{\mathit{gas}\mathit{\text{@}}\mathit{TM}-\mathit{InTe}}-E_{\mathit{TM}-\mathit{InTe}}-E_{\mathit{gas}}$$

(2)

where $E_{\mathit{gas}\mathit{\text{@}}\mathit{TM}-\mathit{InTe}}$ and $E_{\mathit{gas}}$ represent the energies of the TM-InTe with an adsorbed gas and a free gas molecule, respectively. A more negative E_ads indicates greater stability of the adsorption process. Moreover, the adsorption stability can also be qualitatively predicted via charge transfer (Q_T) between the gas and adsorbent, expressed as [38,39] Q_T = Q_i − Q_j, where Q_i and Q_j are the charges of the adsorbed and isolated gas molecules, respectively. The negative Q_T indicates that the adsorbed gas molecule acquires electrons from the substrate.

3. Results and Discussion

3.1. Properties of Ir-InTe and Pt-InTe Monolayers

As shown in Figure 1, the hexagonal InTe monolayer is typically characterized by a Te-In-In-Te stacking sequence, where two inner hexagonal planes of In atoms are covalently bonded to each other and are further sandwiched between two outer hexagonal planes of Te atoms. Electronically, the single-layer InTe is predicted to be an indirect semiconductor with the calculated bandgap and lattice parameter of 1.536 eV and 4.388 Å, which matches well with the previous result (1.44 eV) [40]. To enhance the adsorption efficacy of monolayer InTe towards four SDPs (H₂S, SO₂, SOF₂, and SO₂F₂), this study functionalizes InTe with highly reactive noble metals, Ir and Pt, by considering three distinct doping sites (Intop, Hollow, and Tetop). After full relaxation, the calculated binding energies for different doping configurations (Figure 2a) reveal that both Ir- and Pt-modified InTe systems follow the order: Hollow > Intop > Tetop. This indicates a preferential occupation of Ir and Pt atoms at the Hollow site of InTe, with E_bin values of −4.76 eV and −4.38 eV, respectively. Such strongly negative binding energies further confirm that the Ir and Pt atoms can be stably embedded into the InTe monolayer.

The band structures of the pristine InTe, Ir-InTe, and Pt-InTe monolayers are illustrated in Figure 3. Conductivity is greatly increased by this doping, which lowers the bandgap of the InTe monolayers from 1.536 eV (pristine) to 0.278 eV (Ir-doped) and 0.593 eV (Pt-doped). Figure 4 presents the lowest-energy configurations and differential charge density (DCD) of the Ir-InTe and Pt-InTe monolayers. As shown in Figure 4a,b, the bond distances between Ir/Pt atoms and their three adjacent Te atoms measure approximately 2.659 Å and 2.726 Å, respectively, which are significantly shorter than the sum of atomic radii for Ir/Pt and Te. This strongly supports the formation of Ir-Te and Pt-Te chemical bonds. From Figure 4c,d, Ir and Pt atoms gather a large number of electron-rich regions, while the InTe layer is dominated by electron-deficient regions. Moreover, Ir and Pt atoms acquire approximately 0.422 e and 0.391 e from the InTe monolayer, respectively. This substantial charge transfer illustrates the strong interaction between the dopant atoms and InTe monolayer.

To further unveil the bonding characteristics of Ir-InTe and Pt-InTe systems, the projected density of states (PDOS) was analyzed, as shown in Figure 2b,c. For the Ir-InTe system, strong orbital overlap between the Ir-d and Te-p orbitals is observed in the energy range of −5.00 eV to 2.00 eV, with pronounced resonance peaks appearing at about −3.60 eV, −2.30 eV, and −0.55 eV. This indicates the formation of strong covalent bonds between Ir and Te. Similarly, for the Pt-InTe system, a more localized orbital hybridization occurs between Pt-d and Te-p orbitals in the range of −3.75 eV to 0.50 eV, leading to the formation of Pt–Te chemical bonds. In summary, these findings demonstrate that the Ir-InTe and Pt-InTe monolayers exhibit remarkable structural stability, providing a robust foundation for their application in gas sensing systems.

3.2. Adsorption Characteristics of the SDPs on Ir-InTe Monolayers

This section systematically investigates the adsorption behavior of four representative SDPs on the Ir-InTe monolayer. The calculated adsorption energies, charge transfer, bandgap changes, and recovery times for Ir-InTe adsorption systems are summarized in

Table 1. Summary of key calculated parameters for SDPs adsorption on Ir-InTe and Pt-InTe monolayers, including adsorption energy (E_ads), charge transfer (Q_T), initial bandgap (E_g), bandgap after adsorption (E′_g), and recovery time (τ) at 598 K.

Materials	Gases	Eads, eV	QT, e	Eg, eV	E′g, eV	τ, s
Ir-InTe	H2S	−1.35	+0.279	0.278	0.416	0.24
	SO2	−2.05	−0.043	0.278	0.429	1.87 × 105
	SOF2	−1.88	−0.034	0.278	0.460	6.91 × 103
	SO2F2	−0.11	−0.010	0.278	0.292	8.45 × 10−12
Pt-InTe	H2S	−0.59	+0.195	0.593	0.641	9.35 × 10−8
	SO2	−1.51	−0.020	0.593	0.863	5.27
	SOF2	−1.33	−0.042	0.593	1.035	0.16
	SO2F2	−0.53	−0.041	0.593	1.217	2.92 × 10−8

, with their most stable adsorption configurations and corresponding DCD plots illustrated in Figure 5. For H₂S (Figure 5a), the S atom preferentially binds to the Ir atom, yielding an E_ads of −1.35 eV and an Ir-S bond length of 2.282 Å. While SO₂ exhibits the strongest adsorption capability on the Ir-InTe surface, with an exceptionally high E_ads of −2.05 eV and a short Ir-S bond length of 2.134 Å. Similarly, SOF₂ shows strong chemisorption, characterized by an E_ads of −1.88 eV and an Ir-S bond length of 2.117 Å. These findings confirm that H₂S, SO₂, and SOF₂ all exhibit stable chemisorption on the Ir-InTe. Conversely, the interaction between SO₂F₂ and Ir-InTe is obviously weak, as evidenced by its low E_ads of −0.11 eV and a longer Ir-O bond length of 2.686 Å, indicating that SO₂F₂ primarily undergoes weak physisorption. As shown in the DCD plots (Figure 5e–g), significant electron accumulation occurs between H₂S, SO₂, SOF₂, and the Ir-InTe monolayer, highlighting their strong interactions. Specifically, H₂S donates approximately 0.279 e to the Ir-InTe monolayer, confirming its role as an electron donor. In contrast, SO₂ and SOF₂ gain approximately 0.043 e and 0.034 e, respectively, from the Ir-InTe monolayer, despite their remarkably high adsorption energies. Nevertheless, SO₂F₂ exhibits minimal charge transfer (0.01 e), further corroborating its weak adsorption characteristics.

Figure 6 presents the PDOS for H₂S, SO₂, SOF₂, and SO₂F₂ adsorbed on an Ir-InTe sheet. As shown in Figure 6a, significant orbital hybridization occurs between the Ir-5d and S-3p within the energy range of −8.10 eV to 1.60 eV. Furthermore, prominent overlap peaks are evident at −7.00 eV, −4.70 eV, and −2.73 eV, indicating the formation of an Ir-S covalent bond. For the Ir-InTe@SO₂ system (Figure 6b), strong hybridization between the Ir-5d and S-3p orbitals is observed in two distinct regions: −7.50 eV to −5.50 eV and 0.00 eV to 1.30 eV, indicating a high affinity of Ir-InTe for the SO₂. In the case of SOF₂ adsorption (Figure 6c), the hybridization between the Ir-5d orbital and the S-3p orbital of SOF₂ appears more delocalized, with prominent hybridization peaks at −8.80 eV, −7.40 eV, −5.00 eV, −3.80 eV, and 1.80 eV, indicating a strong interaction between SOF₂ and Ir-InTe. Conversely, the Ir-InTe@ SO₂F₂ system exhibits markedly weaker hybridization, with only a minor peak near −1.25 eV, further suggesting weak physisorption.

Additionally, significant charge transfer is observed between the Ir-InTe and H₂S, SO₂, and SOF₂ molecules, as shown in the insets of Figure 6a–c. This observation confirms the formation of Ir–S chemical bonds in these systems. In contrast, the absence of notable charge transfer between Ir-InTe and SO₂F₂, as evidenced by the largely undisturbed charge density regions, indicates the lack of chemical bonding. Consequently, the adsorption strength of H₂S, SO₂, and SOF₂ is substantially greater than that of SO₂F₂. Furthermore, the band structures of the Ir-InTe adsorption systems are presented in Figure 7. The adsorption of H₂S, SO₂, and SOF₂ results in a significant increase in the bandgap of Ir-InTe, from 0.278 eV to 0.416 eV, 0.429 eV, and 0.460 eV, respectively. This pronounced bandgap modulation enhances the suitability of Ir-InTe for detecting these three gases. In contrast, the adsorption of SO₂F₂ has minimal effect on the bandgap due to weak physisorption.

3.3. Adsorption Properties of the SDPs on Pt-InTe Monolayers

The most stable adsorption configurations of the SDPs on the Pt-InTe monolayer and their corresponding DCD are illustrated in Figure 8, with the corresponding adsorption parameters listed in Table 1. As shown in Figure 8a–c, the H₂S, SO₂, and SOF₂ molecules preferentially interact with the Pt atom of Pt-InTe via their S atoms. The calculated adsorption energies for H₂S, SO₂, and SOF₂ are −0.59 eV, −1.51 eV, and −1.33 eV, respectively, with adsorption distances ranging from 2.162 Å to 2.311 Å. Notably, these distances are notably shorter than the sum of the covalent radii of Pt and S atoms (2.65 Å), providing strong evidence for chemisorption of these three gases. In Figure 8d, SO₂F₂ adsorbs above the Pt atom through its O atom, with an adsorption energy of −0.53 eV and an adsorption distance of 2.201 Å. Significantly, this adsorption distance is comparable to the sum of the atomic radii of Pt and O, indicating that SO₂F₂ adsorption belongs to weak chemisorption. As shown in Figure 8e, the DCD analysis reveals an electron depletion region around H₂S and significant electron accumulation near the Pt atom on the Pt-InTe surface. This implies that H₂S acts as an electron donor, transferring approximately 0.195 e to the monolayer. Conversely, SO₂, SOF₂, and SO₂F₂ function as electron acceptors, gaining about 0.020 e, 0.042 e, and 0.041 e from the Pt-InTe monolayer, respectively.

To elucidate the microscopic interaction mechanisms during adsorption, the PDOS of the Pt-InTe adsorption systems was analyzed, with results presented in Figure 9. For the H₂S adsorption system (Figure 9a), the stable chemisorption is primarily attributed to the significant hybridization between Pt-5d and S-3p orbitals within the energy range of −7.43 eV to 2.00 eV, with three distinct hybridization peaks observed at approximately −6.50 eV, −2.60 eV, and −0.10 eV. In the SO₂ and SOF₂ adsorption systems, as shown in Figure 9b,c, the Pt-5d orbitals exhibit strong hybridization with the S-3p orbitals of the two gases across broader energy ranges. This robust hybridization underscores that the strong electronic interaction between SO₂, SOF₂, and the Pt-InTe monolayer is the primary reason for their high adsorption energies. For the Pt-InTe@SO₂F₂ system (Figure 9d), significant hybridization between the Pt-5d orbital and O-2p orbital of SO₂F₂ is evident, accompanied by distinct overlapping peaks near −6.5 eV, −4.5 eV, and −2.5 eV. Additionally, the band structures of Pt-InTe adsorption systems are depicted in Figure 10. The adsorption of H₂S, SO₂, SOF₂, and SO₂F₂ increases the bandgaps of Pt-InTe from 0.593 eV to 0.641 eV, 0.863 eV, 1.035 eV, and 1.217 eV, respectively. This prominent bandgap modulation effect indicates a high sensitivity of Pt-InTe towards all four SDPs.

3.4. Gas Sensor Explorations

Sensitivity is paramount for gas sensing materials as it directly determines their ability to detect trace amounts of target gases with high precision and reliability, which is critical for applications in the detection of SDPs. The conductivity of these materials is intrinsically linked to their bandgap, and the change in conductivity can serve as the primary detection signal. Thus, the sensitivity can be quantitatively evaluated through the percentage change in bandgap (ΔE_g) or work function changes (ΔΦ), which are defined as [36]:

$$\mathsf{∆}{E}_{\mathrm{g}}={(E}_g^{\prime }-E_g^0)/E_g^0 \times 100\%$$

(3)

$$\mathsf{∆}\Phi ={(\Phi }^{\prime }-{\Phi }^0)/{\Phi }^0 \times 100\%$$

(4)

Here, $E_g^0$ and $E_g^{\prime }$ represent the bandgaps of sensing materials before and after gas adsorption, while ${\Phi }^{\prime }$ and ${\Phi }^0$ denote the work functions of sensing materials with and without gas adsorption.

Figure 11 illustrates bandgap and work function variations in Ir-InTe and Pt-InTe monolayers induced by the SDP adsorption. As depicted in Figure 11a, the pristine InTe monolayer exhibits poor sensitivity towards H₂S, SOF₂, and SO₂F₂ due to minimal ΔE_g values, while demonstrating moderate sensitivity to the SO₂. However, its weak SO₂ adsorption strength limits practical applicability. Conversely, H₂S, SO₂, and SOF₂ adsorption induces substantial bandgap alterations in Ir-InTe, with ΔE_g values of 49.6%, 54.3%, and 65.5%, respectively, indicating that the Ir-InTe is highly sensitive to these gases. Similarly, Pt-InTe displays superior sensitivity to SO₂, SOF₂, and SO₂F₂, as evidenced by ΔE_g values of 45.5%, 74.5%, and 105.2%. As shown in Figure 11b, H₂S adsorption modulates Ir-InTe’s work function from 4.63 eV to 4.30 eV, while SO₂ and SOF₂ adsorption elevates it to 5.14 eV, indicating the exceptional sensitivity of Ir-InTe for these gases. Additionally, all four SDPs induce substantial changes in the work function (ΔΦ) of the Pt-InTe monolayer, ranging from −6.02% to 18.47%, thereby highlighting its potential as a work function-based sensing material. Overall, both Ir-InTe and Pt-InTe monolayers exhibit high SDP sensitivity via bandgap or work function responses.

Selectivity is another critical performance metric for gas sensors, as it defines their ability to differentiate a target analyte from interfering gases. This characteristic can be quantitatively evaluated by comparing the adsorption energy differences (ΔE_ads) among various molecules. For the Ir-InTe, the adsorption energy for H₂S (−1.35 eV) is significantly weaker than that for SO₂ (−2.05 eV) and SOF₂ (−1.88 eV), indicating that SO₂ and SOF₂ can be effectively distinguished from mixtures containing H₂S, SO₂, and SOF₂. Similarly, the Pt-InTe exhibits even greater selectivity, with exceptionally large ΔE_ads values of 0.92 eV between SO₂ and H₂S, and 0.74 eV between SOF₂ and H₂S. These results highlight the excellent potential of these materials for the selective detection of sulfur oxides in complex environments. Moreover, a sensor array approach can further enhance selectivity among different SDPs. For example, while SO₂ and SOF₂ yield similar signals on the Ir-InTe sensor, they generate highly distinct electronic signatures on the Pt-InTe material. By integrating data from both sensors, a unique response pattern for each target gas can be established, enabling robust and reliable identification.

Recovery time is a critical performance metric for a gas-sensitive material, reflecting its ability to revert to the initial state after exposure to a target gas. According to the transition state theory, the recovery time (τ) can be calculated by [41,42]:

$$\tau ={{\upsilon }_0}^{-1}\exp (-E_a/k_{B}T)$$

(5)

where ${\upsilon }_0$, $E_a$, $k_B$, and T represent the attempt frequency, the adsorption energy of a system, the Boltzmann constant, and the absolute temperature, respectively. For the attempt frequency (υ₀), we adopt the commonly used value of 10¹² s⁻¹, which is a standard approximation for gas desorption processes in theoretical studies [43,44].

Figure 12 presents the recovery times of four SDPs desorbing from Ir-InTe and Pt-InTe monolayers at varying temperatures. For the Ir-InTe systems (Figure 12a), the recovery time of SO₂F₂ at 298 K is negligible owing to weak adsorption, which may lead to unstable electrical signals. In contrast, SO₂ and SOF₂ exhibit exceptionally prolonged recovery times of 4.56 × 10²² s and 6.09 × 10¹⁹ s, respectively. Even at 598 K, their recovery times remain exceptionally long, indicating significant challenges in desorbing SO₂ and SOF₂ from the Ir-InTe surface. Consequently, Ir-InTe holds substantial promise as a single-use gas sensing material for SO₂ and SOF₂ detection. Notably, Ir-InTe exhibits suitable recovery times of 45.5 s and 0.24 s for H₂S at 498 K and 598 K, respectively, highlighting its suitability as a reusable high-temperature H₂S sensor. In the Pt-InTe systems (Figure 12b), all four SDPs exhibit either impractically short or excessively long recovery times at 298 K, limiting room temperature reusability. However, at 598 K, Pt-InTe achieves reasonable recovery times of 5.27 s for SO₂ and 0.16 s for SOF₂. In summary, Ir-InTe is promising for reusable H₂S sensing at high temperature, whereas Pt-InTe functions as a recyclable sensor for SO₂ and SOF₂ detection under high-temperature conditions.

4. Conclusions

In this work, the structural, electronic, and gas sensing properties of Ir-InTe and Pt-InTe monolayers towards four SDPs (H₂S, SO₂, SOF₂, and SO₂F₂) were systematically explored via the use of first-principles calculations. The key findings are summarized as follows:

(1)

Ir and Pt atoms stably embed into the hollow sites of the InTe monolayer, driven by strong orbital hybridization between Ir/Pt d and Te p orbitals. These modifications significantly reduce the bandgap of the InTe monolayer.

(2)

The unique d-orbital configurations of Ir and Pt atoms facilitate chemisorption of SDPs. Ir-InTe exhibits strong affinity for H₂S, SO₂, and SOF₂ (|E_ads| ≥ 1.35 eV), while Pt-InTe effectively chemisorbs all four gases, as corroborated by the PDOS, DCD, and charge transfer analyses.

(3)

Ir-InTe is highly sensitive to H₂S, SO₂, and SOF₂, with bandgap change (ΔE_g) values of 49.6%, 54.3%, and 65.5%, respectively, while Pt-InTe displays superior sensitivity to SO₂, SOF₂, and SO₂F₂, as evidenced by the large ΔE_g values of 45.5%, 74.5%, and 105.2%. Furthermore, both monolayers exhibit notable work-function-based sensitivity to H₂S, SO₂, and SOF₂.

(4)

Recovery time analysis suggests that Ir-InTe is a promising reusable sensor for H₂S, whereas Pt-InTe serves as a recyclable detector for SO₂ and SOF₂ under high-temperature conditions. This work provides a theoretical foundation for designing efficient InTe-based sensors for real-time SDP monitoring. To validate the predictions, future research should integrate DFT with synthesis and in situ testing.