First-Principle Insight into the Ru-Doped PtSe2 Monolayer for Detection of H2 and C2H2 in Transformer Oil.

Using first-principles theory, this paper investigates the sensing behavior of the Ru-doped PtSe2 (Ru-PtSe2) monolayer for two dominant gases, namely, H2 and C2H2, in the transformer oil to explore its potential as a gas sensor to evaluate the operation status of the electrical transformers. Ru-doping prefers to go through the S1 site with the largest E b of -3.71 eV. Chemisorption is identified in the H2 and C2H2 systems with E ad obtained as -0.83 and - 2.09 eV, respectively, indicating the stronger performance of the Ru-PtSe2 monolayer upon C2H2 adsorption. Meanwhile, the obvious improvement of bandgap in the C2H2 system suggests the potential of Ru-PtSe2 monolayer as a resistance-type gas sensor for C2H2 detection. Moreover, the applied biaxial strains ranging at 1-5% give rise to various Q T and E g in two systems, indicating the tunable sensing response of the Ru-PtSe2 monolayer for gas detection with modulated strains. Our calculation proposes a novel 2D sensing material for H2 and C2H2 detection, which would be beneficial to stimulate more edge-cutting research in the gas sensing field as well.

Introduction

Electrical transformers are the most significant equipment in the power system for electricity transition and transmission, over 90% of which employs the mineral oil as the insulation medium to ensure their safe operation.[1,2] In the long run, the oil under some inevitable insulation defects such as partial discharge and partial overheat will decompose into several gas species including H2, CH4, C2H2, CO, and C2H4 dissolving into the oil.[3] Among these gas species, H2 and C2H2 account for the dominant content and are widely used as the typical gases to evaluate the operation status of the transformers.[4] Therefore, realizing the sensitive detection of such two typical gases becomes the focus of attention in the field of electrical engineering to conduct the daily maintenance and to banish any latent breakdowns of the transformers as early as possible.[5−8]

With the improvement of 2D-layered materials in recent years, the research in the gas sensing field makes great progress as well since the 2D materials with a large surface area and favorable carrier mobility can perform strong chemical reactivity to the gas species, making them appropriate as sensing materials with high sensitivity.[9,10] Very recently, transition metal dichalcogenides (TMDs) with tunable electronic behavior are widely studied as gas sensing materials, and their responses are also adjustable by modulating the gate voltage or biaxial strains.[11,12] Among these TMDs, PtSe2 is reported exhibiting a semiconducting property with a bandgap of about 1.2 eV in its monolayer form,[13] and it has been theoretically predicted to have a strong potential to be a field-effect transistor sensor.[14] Also, a first-principles calculation has proven that the PtSe2 monolayer has outstanding sensing behavior upon gas molecules with favorable resistance response under biaxial strain.[15] However, the binding force between the gas molecules and the pristine PtSe2 surface is still quite weak (0.1–0.5 eV) to cause enough charge transfer for their sensitive detections, especially in some harsh environments.

To promote the adsorption performance of the sensing materials, transition metal (TM) doping is proposed to enhance the chemical reactivity and catalytic behavior of the nano-surfaces.[16,17] From this regard, the binding force and charge-transfer between the gas molecules and sensing adsorbent can be improved to guarantee higher sensitivity for the targeted gases.[18,19] It has been reported that ruthenium (Ru) has strong catalytic behavior and desirable chemical reactivity in the gas interactions, exerting remarkable promotion for the performance of gas sensing and catalysis.[20,21] Thus, we proposed a Ru-doped PtSe2 (Ru-PtSe2) monolayer in this work to investigate its sensing potential for H2 and C2H2 based on first-principles theory. Our work from the aspect of theoretical prediction attempts to explore a novel sensing material for evaluation of the operation status of the transformers. Such theoretical calculations based on computational science have been proven as a workable and highly effective approach to this end.[22,23] Moreover, we are hopeful that our results would be helpful to provide guidance for further experimental researches in the field of 2D sensing materials.

Results and Discussion

Ru-Doping on the PtSe2 Monolayer

The Ru-PtSe2 monolayer is determined by doping one Ru atom on the pristine PtSe2 monolayer, on which we consider three possible sites, as exhibited in Figure a. The binding energy (Eb) is used to evaluate the binding force between the Ru dopant and PtSe2 monolayer, as calculated bywhere ERu-PtSe, ERu, and EPtSe are the total energies of the Ru-PtSe2, single Ru atom, and pristine PtSe2 monolayer, respectively. According to our geometric optimization, it is found that the Ru dopant preferred to be trapped on the S1 site, namely the top of the second-layered Pt atom, with the largest Eb obtained. The related structure would be called as the stable configuration (MSC) of the Ru-PtSe2 monolayer, as plotted in Figure b. Moreover, the charge density difference (CDD) of the Ru-PtSe2 monolayer is plotted in Figure c as well to illustrate the bonding nature during Ru doping on the pristine PtSe2 surface.

Figure 1

Structures of (a) PtSe2 monolayer. (b, c) MSC and CDD of the Ru-PtSe2 monolayer. In CDD, the green (purple) areas are electron accumulation (depletion) with an isosurface of 0.01 e/Å3.

Based on our definition, the Eb is obtained as −3.71 eV for Ru-doping on the S1 site, whereas it is 1.60 eV for the S2 site and – 2.91 eV for the S3 site, respectively. After doping, the Ru dopant is bonded with three Se atoms on the first layer of the PtSe2 monolayer, forming three Ru–Se bonds measured equivalently as 2.39 Å, slightly shorter than the sum covalent radii of Ru and Se atoms (2.41 Å[24]). In addition, the structure of the PtSe2 supercell is somewhat deformed after Ru doping, wherein the Pt–Se bonds are slightly elongated to 2.58–2.72 Å from that of 2.54 Å in the pristine counterpart. These findings indicate the strong binding force for Ru doping on the PtSe2 surface, which leads to the stable formation of Ru–Se bonds accordingly. According to the Hirshfeld analysis, the Ru dopant is positively charged by 0.085 e in the Ru–PtSe2 system, suggesting its electron-donating behavior when interacting with the PtSe2 surface, which behaves as the electron acceptor instead. From the CDD, the electron accumulation is mainly localized on the Ru–Se bonds, while the electron depletion is mainly on the Ru dopant, which supports the electron-releasing behavior of the Ru dopant and the strong electron hybridization on the Ru–Se bonds.

The electron-donating behavior of the Ru dopant will exert a significant impact on the electronic behavior of the PtSe2 monolayer. To expound this issue more visually, Figure gives the band structure (BS) and density of state (DOS) of the Ru-PtSe2 system. As reported, the pristine PtSe2 monolayer is an indirect semiconductor with a bandgap of about 1.2 eV.[15] In this work, it is found from Figure a that the bandgap of the Ru-PtSe2 monolayer is obtained as 0.009 eV, quite a small value indicating its metallic-like electrical conductivity. Meanwhile, the top of the valence band is localized on the Γ point, while the bottom of the conduction band is localized on the K point, which manifests the indirect semiconducting property of the Ru-PtSe2 system. That is, Ru doping significantly enhances the electrical conductivity of the PtSe2 monolayer but does not modify its indirect semiconducting property. From Figure b where the DOS of pristine and Ru-doped PtSe2 systems are shown, it is seen that there is a large bandgap over the Fermi level of the pristine PtSe2 system, while the DOS of the Ru-PtSe2 monolayer is almost continuous at the Fermi level, verifying its strong electrical conductivity. This could be attributed to the remarkable state contribution from the Ru dopant, which exerts a large impact around the Fermi level. In addition, the DOS of the Ru-PtSe2 monolayer is left-shifted compared with the pristine counterpart, which results from the electron-accepting behavior of the PtSe2 surface from the Ru dopant that improves the effective Coulomb potential accordingly.[25] In terms of the formation of Ru–Se bonds, Figure c gives the electronic evidence. One can see in this figure that the Ru 4d orbital is highly hybrid with the Se 3p orbital at −7.5 to 1.2 eV, which illustrates the strong electron hybridization between the Ru and Se atoms and leads to a strong orbital interaction on the Ru–Se bonds.[26]

Figure 2

(a) BS of the Ru-PtSe2 system, (b) DOS comparison, and (c) orbital DOS. The value in the BS is the bandgap, and the dashed line in DOS is the Fermi level.

Gas Adsorption on the Ru-PtSe2 Monolayer

The adsorption behavior of the Ru-PtSe2 monolayer upon H2 and C2H2 is conducted to study its sensing performance upon the targeted gaseous species. At the same time, the adsorption of CH4 and C2H4 are also studied for better comparison since they are also the gas species in the transformer oil and may affect the adsorption of H2 and C2H2. Figure plots the MSC and CDD of the H2 and C2H2 systems, and Figure S1 plots the MSC of the CH4 and C2H4 systems. It is found that the Ru-PtSe2 monolayer exhibits weak interactions with CH4 and C2H4 molecules, with small Ead (−0.16 eV for the CH4 system and −0.77 eV for the C2H4 system) identified as physisorption for the adsorption systems. Thus, it could be assumed that they can exert small impact on the sensing of H2 and C2H2 in the mixed gas environment given their small content, which would be not be analyzed in detail in the following sections.

Figure 3

MSC and CDD of (a) H2 and (b) C2H2 adsorption on the Ru-PtSe2 monolayer. The set in CDD is the same as that in Figure .

In the H2 system, one can see that the H2 molecule standing on the top-left corner of the Ru dopant is captured by two new-formed Ru–H bonds, with bond lengths of 1.68 and 1.69 Å, respectively. The H–H bond of the H2 molecule is broken after adsorption, with an atomic distance of 0.97 Å, much larger than that in its isolated gas phase of 0.75 Å. At the same time, the Ru–Se bonds are elongated to 2.40, 2.42, and 2.49 Å, respectively. These geometric deformations suggest the strong binding force between the Ru dopant and the H2 molecule that leads to the remarkable activation in their structures.[27] Moreover, the large Ead of −0.83 eV also confirms the strong binding force for H2 adsorption on the Ru-PtSe2 surface. According to the Hirshfeld analysis, 0.041 e is transferred from the Ru-PtSe2 monolayer to the H2 molecule, and the Ru dopant is positively charged by 0.054 e. These results manifest that Ru dopant accepts 0.031 e from the PtSe2 monolayer while the PtSe2 monolayer loses 0.072 e in total during H2S adsorption. In the CDD, one can see that the electron accumulation is mainly localized on the Ru–H bonds and the Ru dopant, and the electron depletions are mainly on the H–H bond and the Ru–Se bonds. These verify not only the formation of Ru–H bonds where the electron localization occurs and the breakage of H–H bond where electron is depleted but also the electron-accepting behavior of the Ru dopant in H2 adsorption.[28]

For C2H2 adsorption onto the Ru-PtSe2 monolayer, it is seen that the C2H2 molecule is trapped on the top of the Ru dopant through two Ru–C bonds with bond lengths of 2.02 and 2.03 Å, respectively. The inner C≡C bond in the C2H2 molecule is elongated to 1.30 Å from that of 1.21 Å in its gas phase. Meanwhile, the C2H2 molecule is distorted after adsorption, in which the two C–H bonds turn upward, making such a linear molecule deformed instead. In addition, the Ru–Se bonds of the Ru-PtSe2 monolayer experience somewhat elongation as well, measured as 2.43, 2.43, and 2.51 Å, respectively. Thus, the further elongation of Ru–Se bonds and the deformation in the C2H2 molecule in this system compared with that of the H2 system implies the strong binding force of the Ru-PtSe2 monolayer for C2H2 adsorption. The much larger Ead of −2.09 eV supports such assumption strongly, which is over 2.5 times than the Ead of −0.83 eV for the H2 system. According to the Hirshfeld analysis, 0.049 e is transferred to the C2H2 molecule, and the Ru dopant is positively charged by 0.094 e. These findings imply the electron-accepting behavior of the C2H2 molecule and electron-donating behavior of the Ru dopant and PtSe2 monolayer, which lose 0.009 and 0.040 e, respectively, in this system. From the CDD, the electron accumulation is mainly localized on the Ru–C bonds, and the electron depletions are mainly on the Ru–Se and C≡C bonds, which confirms the formation of Ru–C bonds and weakness of the Ru–Se and C≡C bonds.

Given the large values of Ead in two systems, we can infer that the Ru-PtSe2 monolayer conducts strong chemisorption upon H2 and C2H2,[29] especially for the C2H2 in which the Ead is over 2.5 times than that of H2. Moreover, to highlight the enhancement of Ru doping for gas adsorption, we perform the adsorption of H2 and C2H2 on the pristine PtSe2 monolayer with the MSC shown in Figure S2. One can see that the Ead for H2 and C2H2 adsorption are obtained as −0.07 and – 0.17 eV, with the adsorption distance of 3.65 and 3.75 Å, respectively. Such findings illustrate the desirable enhancement of the Ru dopant for gas adsorption. In other words, the Ru dopant exerts strong catalytic behavior in the gas interaction and promotes the adsorption strength around the Ru center. In addition, the Ru dopant behaves as an electron acceptor in the H2 system and electron donator in the C2H2 system. Thus, it could be assumed that the Ru dopant is an electron bridge connecting the charge transfer between the PtSe2 surface and the gas molecules. Also, the charge transfer would lead to the electron redistribution in the Ru-PtSe2 system, which in return can deform its electronic behavior accordingly. We would highlight this part of analysis in the next section.

Since in some moist environment the adsorption behavior of the Ru-PtSe2 monolayer upon H2 and C2H2 would also be affected, this work conducts the simulations of H2 and C2H2 adsorption onto the Ru-PtSe2 surface with a H2O molecule pre-adsorbed to analyze the impact of the humidity in the atmosphere on gas adsorptions. The MSC for H2O adsorption and H2/H2O and C2H2/H2O co-adsorption is exhibited in Figure . It is found that the Ru-PtSe2 monolayer exhibits good adsorption behavior upon the H2O with an Ead of −0.91 eV. However, the adsorption behavior upon H2 and C2H2 somewhat declined with the pre-adsorbed H2O, compared with the isolated Ru-PtSe2 systems. These findings suggested that the existence of moisture would weaken the sensing behavior of the Ru-PtSe2 monolayer, and the scavenging of humidity is important to guarantee the good sensing response for gas detection instead.

Figure 4

MSC of (a) H2O adsorption, (b) H2/H2O co-adsorption, and (c) C2H2/H2O co-adsorption.

Electronic Property upon Gas Adsorption

To analyze the electronic behavior of the Ru-PtSe2 monolayer upon H2 and C2H2 adsorption, we display the BS and DOS of two systems in Figure . The molecular DOS of the gases before and after gas adsorption is analyzed to illustrate the electronic activation upon the gas molecules, while the orbital DOS of the bonded atoms is analyzed to illustrate the orbital interactions of these atoms.

Figure 5

BS and DOS of (a1–a3) H2 system and (b1–b3) C2H2 system.

In the BS of H2 and C2H2 systems, one can see that the bandgaps are calculated to be 0.071 and 0.141 eV, respectively, much larger than that of 0.009 eV in the pure Ru-PtSe2 system, indicating the reduced electrical conductivity of the Ru-PtSe2 monolayer after H2 and C2H2 adsorptions. In addition, the top of the valence and the bottom of the conduction band are both localized on the K point in the H2 system and are both localized on the Γ point in the C2H2 system, implying that adsorption of H2 and C2H2 would alter the indirect semiconducting property of the Ru-PtSe2 system. Moreover, the much larger bandgap in the C2H2 system compared with that in the H2 system suggests the better sensing response of the Ru-PtSe2 monolayer upon C2H2.

In the molecular DOS of H2 and C2H2, it is found that their DOS stats are afflicted with remarkable deformations after adsorption, in which the states are split into several smaller states and left-shifted to a region below the Fermi level. This may be attributed to the electronic activation upon the gas molecules caused by the orbital interaction, and the activated states would contribute to the total DOS effectively, which then deform the electronic behavior of the whole system. Apart from that, it is the activated states of the gas molecules that hybridize with the Ru dopant that facilitates the formation of new bonds where the orbital interaction occurs.[30] From the atomic DOS, one can see that the Ru 4d orbital is in hybrid with the H 1s orbital at −7.9, −1.1, and 0–0.5 eV in the H2 system, while it is in hybrid with the C 2p orbital at −8.5, −4.4, −3.1, and −0.2 to 1.2 eV in the C2H2 system. The hybrid peaks are where the activated peaks of the gas molecules localized in the adsorbed system, which verifies the assumption above. In addition, these hybridizations also manifest the orbital interactions on the Ru–H and Ru–C bonds, confirming their strong binding force.

Resistance-Type Sensor Exploration

The above analysis manifests that the electronic behavior of the Ru-PtSe2 monolayer would be deformed after H2 and C2H2 adsorptions, wherein the improvement of the bandgap can provide the basic evidence for the decline of its electrical conductivity in the gas environment, as evaluated in the following formula:[31]wherein σ is electrical conductivity, λ is a constant, Bg is the bandgap, k is the Boltzmann constant, and T is temperature. Based on our calculations, the bandgap is increased by 0.062 and 0.132 eV in the H2 and C2H2 systems, respectively. Therefore, one can predict that the decline of electrical conductivity in the Ru-PtSe2 monolayer would be detectable in the C2H2 system, while the sensing response in the H2 system is not convincing given the slight shake in its bandgap. This provides the basic sensing mechanism for exploration of the Ru-PtSe2 monolayer as a resistance-type gas sensor for C2H2 detection with favorable electrical response, which would be much higher than that for H2, CH4, and C2H4 detection. However, the selective detection for the C2H2 in the mixed gas environment including such four gas species is not able to be realized using such a sensing material. Therefore, the separation of mixed gases in the transformer oil is essential to realize the effective detection of C2H2 and to evaluate the operation status of the transformers.

In addition, the recovery time of the Ru-PtSe2 monolayer is also an important parameter to evaluate its repeatability for gas detection, which can be calculated based on the van’t Hoff–Arrhenius equation:where A is the attempt frequency (1012 s–1), T is temperature, and KB is the Boltzmann constant (8.318 × 10–3 kJ/(mol·K)). Ea is determined to be equal as Ead in this work. From this formula, the H2 desorption from the Ru-PtSe2 monolayer would be feasible at room temperature (298 K) with a time of 95.6 s, and C2H2 desorption would be quite difficult. Through the increase in temperature, it is found that the recovery time for the C2H2 system can be decreased to 2.3 × 1011 s at 450 K and to 1046.7 s at 700 K. That is, the reusability of the Ru-PtSe2 monolayer for C2H2 sensing becomes possible with a desorption temperature of 700 K.

However, the increase in temperature causes the stability of the Ru-PtSe2 monolayer to be another issue. Thus, we perform the molecular dynamic simulation for the Ru-PtSe2 monolayer during the period of 1 ps (1000 fs) at 450 and 700 K to verify its thermostability, with related geometries shown in Figure S3. One can see from this figure that the Ru-PtSe2 surface suffers somewhat deformations at the high temperatures, wherein the Ru dopant experiences slight displacement. Nevertheless, the morphology of the system is not significantly impacted, without bond breakage after simulations. These results manifest the desirable thermostability of the Ru-PtSe2 monolayer at 450 and 700 K. At the same time, the vibrational analysis implies that the frequency of the Ru-PtSe2 monolayer varies at 70.2–679.4 cm–1, which indicates that there has no virtual frequency in the system, further verifying the good chemical stability of the Ru-PtSe2 monolayer. All these analyses above prove the strong potential of the Ru-PtSe2 monolayer to be a promising gas sensor with admirable repeatability.

Effect of Strain upon Gas Adsorption

The ABA structure of the PtSe2 monolayer is strain sensitive and is a potential piezoelectric material for gas detection.[32] From the theoretical aspect, the adsorption parameters related to the sensing response can be obtained by modulating the geometric lattice.[33] In this section, we adopt various biaxial strains (ε) to study the dependence of the QT and Eg of the Ru-PtSe2 monolayer upon H2 and C2H2 adsorption, as calculated bywhere a0 and a are the lattice parameters of the Ru-PtSe2 supercell with and without strain, respectively. In this work, the strain is set, increasing from 1 to 5%, with lattice constants of 3.68, 3.65, 3.61, 3.57, and 3.53 Å, respectively.

Figure portrays the schematic of the applied strain the related dependences upon QT and Eg. One can see that with the increase in strain in the positive direction, the charge transfer is decreased in the H2 system from 0.049 to 0.068 e as the strain increases from 1 to 5%, while it is increased in the C2H2 system from 0.041 to 0.018 e as the strain increases at the same range. Although such two gases still retain the electron-accepting property, it is predictable that the charge-transferring path in the H2 system would be conversed if the applied strain continually increases. When it comes to the bandgap of the gas-adsorbed systems, one can see that it is decreased with the increase in the applied strain, and the C2H2 system is more likely to be affected by the varying of the strains, which experiences a much larger range of 0.141–0 eV compared with that of 0.071–0.034 eV in the H2 system as the strain increases from 1 to 5%. In other words, the Ru-PtSe2 monolayer has stronger sensitivity upon C2H2 detection with the modulation of biaxial strains, though both systems are strain sensitive to obtain diverse sensing responses.

Figure 6

Effect of strain on the adsorption parameters of the Ru-PtSe2 monolayer. (a, b) Schematic of applied strain, the direction of the arrow is the positive strain. (c) Dependence of QT and (d) dependence of Eg.

It is interesting to note that when the biaxial strain reaches to 5%, the bandgap of the Ru-PtSe2 monolayer after C2H2 adsorption is obtained as 0 eV, indicating the metallic property of the system. To better understand this issue, the adsorption configuration of the C2H2 system with a strain of 5% and related BS distribution are displayed in Figure . One can see that the morphologies of the Ru-PtSe2 monolayer suffer somewhat deformation under 5% strain, but the C2H2 adsorption configuration is not significantly impacted. In the BS, there is a state on the bottom of the conduction band crossing the Fermi level, thus leading to the metallic behavior of this system. These findings verify the tunable sensing response of the Ru-PtSe2 monolayer for gas detection with modulated strains.

Figure 7

(a) Adsorption configuration of the C2H2 system with a strain of 5% and (b) related BS.

In short, the Ru-PtSe2 monolayer is a potential piezoelectric material for gas detection to modify the sensing response under various biaxial strains. Through the modulation of the applied biaxial strain, the electron redistribution would occur in the adsorption systems, which will affect the bandgap of the Ru-PtSe2 monolayer, which provides the tunable sensing behavior for gas detections.

Conclusions

In this paper, the first-principles theory is applied to investigate the sensing behavior of the Ru-PtSe2 monolayer upon H2 and C2H2 so as to explore its potential as a gas sensor for evaluation of the operation status of the transformer. A single Ru atom is doped on the pristine PtSe2 surface to establish the Ru-PtSe2 supercell. The main conclusions are as follows:

The Ru dopant preferred to be trapped on the S1 site of the PtSe2 surface with an Eb of −3.71 eV, which brings the bandgap of the Ru-PtSe2 monolayer as 0.009 eV.

Chemisorption is identified for H2 and C2H2 adsorption on the Ru-PtSe2 surface, and the stronger interaction in the C2H2 system causes larger improvement in the bandgap for feasible detection.

The Ru-PtSe2 monolayer is a promising piezoelectric material for gas detection via the modulation of the applied strain, with tunable QT and Eg obtained in various strains.

This theoretical report proposes a novel sensing material for C2H2 detection, which would be meaningful in the field of electrical engineering to evaluate the operation status of the electrical transformers in the power system.

Computational Details

In this work, the spin-polarized calculations for structural optimization and electronic property were all implemented within the DMol3 package.[34] The Perdew–Burke–Ernzerhof (PBE) function within the generalized gradient approximation (GGA) was adopted to handle the electron exchange-correlation terms.[35] Meanwhile, we used Tkatchenko and Scheffler’s (TS) method to understand the van der Waals force and long-range interactions.[36] Double numerical plus polarization (DNP) was determined as the atomic orbital basis set.[4] The Monkhorst pack k-point was sampled to 10 × 10 × 1 to deal with the geometric optimization and electronic properties.[37] The energy tolerance accuracy, maximum force, and displacement were defined as 10–5 Ha, 2 × 10–3 Ha/Å, and 5 × 10–3 Å, respectively,[38] whereas a self-consistent loop energy of 10–6 Ha, global orbital cut-off radius of 5.0 Å, and smearing of 0.005 Ha were selected for the static electronic calculations to ensure the accuracy of total energy.[39]

We established a 3 × 3 × 1 supercell for the pristine PtSe2 monolayer to conduct the whole calculations below, and a vacuum region of 15 Å was used to prevent possible interactions between the adjacent units.[40] After geometric optimization, the lattice constant of the pristine PtSe2 supercell was 3.72 Å, in accordance with that of 3.71 Å in ref (14). The binding force between the gas molecule and the Ru-PtSe2 surface was evaluated by the adsorption energy (Ead), as calculated by[41,42]where ERu-PtSe, ERu-PtSe, and Egas represent the total energies of the Ru-PtSe2/gas system, pure Ru-PtSe2 system, and isolated gas molecule, respectively. Meanwhile, we considered the charge transfer (QT) in the gas adsorption systems by Hirshfeld analysis, whose negative values indicated the electron-accepting behavior of the adsorbed gas species. In addition, Hirshfeld analysis would not be affected by the basic set of the calculations,[26] which guarantee the good accuracy of our results. To meet the applied condition of the Ru-PtSe2 monolayer in the power system, the simulations are all conducted under room temperature, and the effect of temperature on the sensing behavior is not considered in this work.