Molecular Insights into the Insulating and Pyrolysis Properties of Environmentally Friendly PMVE/CO₂ Mixtures: A Collaborative Analysis Based on Density Functional Theory and Reaction Kinetics

Abstract

Perfluoromethyl vinyl ether (PMVE) has recently emerged as a promising environmentally friendly insulating gas with potential for practical applications in the power industry. When mixed with CO₂, the PMVE/CO₂ mixture exhibits an elevated liquefaction temperature and enhanced insulation performance, making it suitable for engineering use. In this study, density functional theory (DFT) calculations were employed to investigate the reactive sites of PMVE molecules. The results indicate that the C₂–O and C₃–O bonds are the most susceptible to breakage, highlighting their high reactivity. The optimal insulation performance of the PMVE/CO₂ mixture is achieved at a CO₂ concentration of approximately 60%, with significant molecular decomposition observed at temperatures exceeding 2600 K. The primary decomposition products include C₂F₂, COF₃, COF₂, F, C₂F₃, CO, CF₃, and C₂F₄. Both high temperature and elevated CO₂ content accelerate the decomposition process. These findings provide valuable insights into the insulation properties and thermal stability of the PMVE/CO₂ system, offering theoretical support for its potential application in eco-friendly high-voltage insulation technologies.

1. Introduction

Sulfur hexafluoride (SF6) is a colorless, odorless gas with superior dielectric and arc-quenching properties and has been extensively utilized in medium- and high-voltage electrical equipment, including gas-insulated circuit breakers (GCBs) and cubicle-type gas-insulated switchgear (C-GIS), for over six decades [1,2]. However, SF₆ is recognized as one of the most potent greenhouse gases, with a global warming potential (GWP) of 23,900 and an atmospheric lifetime exceeding 3200 years [3,4,5]. In 1997, the Kyoto Protocol designated SF₆ as one of the six greenhouse gases subject to international regulation [6]. As global climate policies have tightened, especially in the power sector, the reduction in SF₆ emissions has become an environmental imperative. Consequently, the development of low-GWP alternatives with comparable insulation performance is a critical pathway toward sustainable and climate-resilient electrical infrastructure.

In recent years, several high-performance alternative insulating media have attracted increasing attention in the power sector [3,7,8,9,10]. These include gases such as C₄F₇N, CF₃I, perfluorocarbons (PFCs) like c-C₄F₈, C₂F₆, C₃F₈, and perfluoroketones (C_nF_2nO). Among them, C₄F₇N demonstrates superior dielectric strength and excellent arc-quenching capability compared to SF₆ and has already been deployed in 145 kV gas-insulated switchgear (GIS) and 420 kV gas-insulated lines (GILs) [11]. However, its relatively high liquefaction temperature and ongoing concerns regarding chronic toxicity have limited broader adoption [12]. CF₃I exhibits better insulation properties than SF₆, with a significantly lower GWP and shorter atmospheric lifetime, making it a promising candidate. Nevertheless, its high biological toxicity and classification by the International Agency for Research on Cancer (IARC) as a Group 3 mutagen have raised safety concerns and constrained its practical use [3]. Perfluorocarbon-based gases generally exhibit high GWPs and long atmospheric lifetimes, posing challenges to their compatibility with low-carbon, environmentally sustainable development goals. Although perfluoroketones such as C₆F₁₂O and C₅F₁₀O show favorable environmental characteristics, their high liquefaction temperatures of 49 °C and 24 °C mean that they exist as liquids under ambient conditions and therefore cannot be used as standalone gas insulating media [13]. These limitations underscore the urgent need to develop novel insulating gases that offer a balanced combination of high dielectric performance, low liquefaction temperature, and minimal environmental impact.

In November 2023, the Korea Electrical Engineering Research Institute (KERI) announced a newly developed environmentally friendly insulating gas, referred to as “K6.” This gas successfully passed the International Electrotechnical Commission (IEC) circuit-breaking performance test and has since undergone pilot deployment in 145 kV high-voltage circuit breakers [14]. Subsequent studies by Xiao Song and collaborators identified the primary component of K6 as C₃F₆O, also known as PMVE. Notably, pure PMVE exhibits an extremely low global warming potential (GWP), estimated at less than one millionth of that of SF₆, along with a significantly shorter atmospheric lifetime and zero ozone depletion potential, underscoring its excellent environmental compatibility. In addition to its environmental advantages, PMVE demonstrates promising electrical insulation characteristics. Theoretical investigations by South Korean researchers have highlighted its potential as a viable SF₆ substitute. For instance, Yeunsoo Park et al. measured the total electron scattering cross-section (TCS) of PMVE and confirmed its favorable electron interaction properties [15]. Furthermore, Nidhi Sinha’s group examined the dielectric strength of PMVE through electron collision experiments, revealing that its critical dielectric strength (475 Td) exceeds that of SF₆ (355 Td) [16]. An experimental study by Xiao Song and Zhang Xiaoxing further evaluated the AC breakdown behavior, partial discharge characteristics, and dielectric recovery performance of PMVE. Their results showed that PMVE exhibits stable breakdown voltage under non-uniform electric fields and a narrow gap between partial discharge inception voltage (PDIV) and partial discharge extinction voltage (PDEV), which is advantageous for suppressing discharge activity [17].

Although PMVE exhibits excellent insulation performance, its tendency toward spontaneous combustion and relatively high liquefaction temperature limit its effectiveness as a standalone insulating medium. To address these challenges, PMVE is typically blended with noble gases to enhance its safety and modify its physical properties. Among potential additives, CO₂ has attracted particular interest due to its favorable insulating and arc-quenching characteristics, as well as its low boiling point, making it a suitable buffer gas in gas mixtures [18]. Nidhi Sinha and colleagues investigated the synergistic effects of combining PMVE with buffer gases and reported a notable enhancement in insulation performance when CO₂ was used as the additive. Specifically, when the PMVE/CO₂ mixture ratio approached 60%, the dielectric strength of the blend was found to be comparable to that of pure SF₆ [16]. Despite these promising findings, current research remains predominantly focused on the properties of pure PMVE, while investigations into the behavior and performance of PMVE/CO₂ mixtures are still limited.

Partial discharge, arc discharge, and spark discharge are common fault phenomena in power equipment, typically originating from insulation defects [19]. Among these, the local temperature during partial discharge can range from 700 to 1200 K, while arc discharges may generate temperatures as high as 3000 to 12,000 K [20]. These extreme thermal conditions can induce the decomposition of insulating gases, leading to the formation of reactive free radicals and various degradation by-products. The accumulation of such decomposition products may deteriorate the dielectric properties of the insulating medium and pose serious risks to the operational safety of electrical systems [21]. Given these concerns, it is of both theoretical and practical importance to investigate the high-temperature decomposition behavior and underlying mechanisms of PMVE/CO₂ gas mixtures. Such studies are essential for assessing the long-term reliability, thermal stability, and environmental suitability of these emerging insulation alternatives in high-voltage applications. It is worth noting that a certain discrepancy exists between the simulation temperature in ReaxFF-MD and the actual experimental temperature. By fine-tuning the force field parameters, the time-dependent decomposition rate of the PMVE/CO₂ mixture could be monitored within the simulation range, effectively narrowing the gap between the simulated and actual decomposition behavior.

This study employs density functional theory (DFT) to investigate the fundamental properties and molecular stability of PMVE, identifying its potential decomposition sites. Ab initio molecular dynamics (AIMDs) simulations were used to evaluate the ionization energy, electron affinity, and excitation energy of PMVE/CO₂ mixtures, aiding in the selection of optimal mixing ratios for engineering use. Thermal decomposition behaviors under varying temperatures and ratios were further explored via ReaxFF molecular dynamics, focusing on key decomposition products and concentrations. Transition state theory and thermodynamic analyses revealed reaction pathways and product distributions, supporting the use of gas chromatography for monitoring equipment status and developing safety measures. These findings establish a link between molecular properties and macroscopic insulation performance, providing theoretical support for PMVE/CO₂ as a sustainable insulating gas alternative.

2. Calculation Methods

2.1. Density Functional Theory Simulation

2.1.1. PMVE Model Construction

According to the Gaussian PMVE model, the bond structure of PMVE consists of C=C double bonds, C-F single bonds, and C-O single bonds. The molecular configuration of PMVE is shown in Figure 1. The structure was optimized using the B3LYP/cc-pVTZ basis set. These key bond length parameters are consistent with those reported in reference [22], confirming that the computational results obtained using the B3LYP/cc-pVTZ basis set are reliable.

2.1.2. Calculation Method

Density functional theory (DFT) is a quantum mechanical computational method that focuses on the electron density outside the atomic nucleus. By calculating the ground-state energy, DFT allows for the determination of molecular system properties and the acquisition of molecular electrical characteristics. This theoretical approach has been widely used in studies of SF₆ substitute gases [23,24,25]. The fundamental insulating properties of these gases are closely related to their microscopic structures. The stability of dissociation reactions can be evaluated by calculating bond strengths and charge distributions. Furthermore, to validate the decomposition pathways of PMVE, transition state searches and reaction enthalpy calculations are performed.

In this study, the Gaussian 16 software package [26] was used to optimize all molecular structures employing the B3LYP [27] functional along with the cc-pVTZ basis set [28,29], and Grimme’s D3BJ dispersion [30] was also considered. To further improve the accuracy of the results, the zero-point energy (ZPE) and enthalpy corrections were carried out [31]. The formula used to calculate the reaction energy is as follows:

$$\mathrm{\Delta }E=E_{Products}-E_{Reactants}$$

(1)

where ΔE represents the reaction energy, E_Products is the energy of the products calculated after geometric optimization, and E_Reactants is the energy of the reactants.

2.2. Molecular Dynamics and Reaction Dynamics Simulation

2.2.1. PMVE/CO₂ Model Construction

To investigate the macroscopic properties of PMVE/CO₂ gas mixture at various temperatures, a periodic cubic structure model was constructed using Materials Studio. The model consists of multiple PMVE and CO₂ molecules, with the number of PMVE molecules set to 100 to balance computational efficiency.

Table 1. Parameters of PMVE/CO₂ system.

No.	CO2 Content	PMVE	CO2	Density (g/cm3)	Box Length (Å)
1	0%	100	0	0.00690	214.1
2	30%	100	160	0.00297	236.4
3	40%	100	250	0.00217	276.4
4	50%	100	380	0.00194	301.5
5	60%	100	570	0.00177	339.4

presents the key system parameters and simulation conditions, including density, CO₂ composition, and box dimensions. These parameters were chosen to replicate the conditions of the gas at 25 °C and 0.1 MPa. The constructed gas mixture model is shown in Figure 2.

2.2.2. Calculation Method

Reaction dynamics is a simulation method that combines the ReaxFF reaction force field and molecular dynamics developed by van Duin and Goddard [32]. This method makes up for the defect that traditional force fields cannot be applied to complex systems and has been widely used to explore the decomposition process of insulating gases [33]. The ReaxFF reaction force field divides the system energy into several parts for calculation and describes the energy of each part except the bond level on the basis of the bond level. The calculation formula of the system energy is as follows:

$$\begin{array}{l}{E}_{\mathrm{system}}=E_{\mathrm{bond}}+E_{\mathrm{over}}+E_{\mathrm{under}}+E_{\mathrm{val}}\\ \begin{array}{cc}& \end{array}+E_{\mathrm{pen}}+E_{\mathrm{tors}}+E_{\mathrm{coa}}+E_{\mathrm{H}-\mathrm{bond}}\\ \begin{array}{cc}& \end{array}+E_{\mathrm{conj}}+E_{\mathrm{vdWaals}}+E_{\mathrm{Coulomb}}\end{array}$$

(2)

where E_system represents the total energy of the system, E_bond is the bond energy, and E_over and E_under are the energy correction terms for overcoordination and undercoordination, respectively. E_val, E_pen, and E_coa correspond to the bond angle energy term, penalty energy term, and three-body conjugation term, respectively. E_H-bond represents the hydrogen bonding energy, E_tors refers to the torsion energy, and E_conj denotes the four-body energy conjugation. E_vdWaals and E_Coulomb represent the non-bonding van der Waals and Coulomb interactions, respectively.

In reaction kinetics simulations, an appropriate increase in temperature can accelerate the reaction rate without altering the reaction path or process [34]. Since the time scale in simulations differs significantly from that of real-world reactions, the reaction is typically accelerated by raising the temperature.

To investigate the decomposition mechanism of the PMVE/CO₂ mixture, the NVE ensemble was first used to optimize the system for 5 ps at 5 K. This was followed by equilibration using NVT and NPT ensembles for 5 ps at 300 K. Molecular dynamics simulations were then performed for 1000 ps using the NVT ensemble at various temperatures, with the 1000 ps simulation time deemed sufficient to analyze the main cleavage products and cleavage pathways. Periodic boundary conditions were applied throughout the simulation, with temperature controlled using the Berendsen method and a temperature coupling coefficient of 0.1 ps. The simulation time step was set to 0.1 fs [35]. Finally, the enthalpy of the cleavage pathway of the PMVE/CO₂ mixture was calculated based on reaction kinetics (ReaxFF-MD), and the potential transition states of the reaction were identified. The difficulty of the cleavage path was assessed from a thermodynamic perspective, validating the reliability of the reaction kinetics simulation results.

2.3. First Principles Simulation

First-principles simulations were conducted using CP2K software to investigate the insulation properties of PMVE/CO₂ systems at various mixing ratios. Input files for CP2K were generated using Multiwfn software developed by Dr. Tian Lu [36]. Geometric optimizations employed the PBE functional with D3 dispersion correction and the MOLOPT basis set (DZVP-MOLOPT-SR-GTH). Subsequent energy calculations utilized the same functional but with a more precise basis set (TZVP-MOLOPT-SR-GTH) [37]. The orbital transformation (OT) method was selected for self-consistent field (SCF) convergence [38]. In this study, the ionization energy, electron affinity, and excitation energy of PMVE/CO₂ gas mixtures were calculated using the aforementioned methods. Subsequently, wavefunction analyses were performed on all structural models using the Multiwfn software [36]. These analyses aimed to evaluate the insulation properties of the mixed systems.

3. Results and Analysis

3.1. Molecular Structure and Properties of PMVE

3.1.1. Bond Strength Analysis

The bond strength of PMVE can be assessed through factors such as bond length, bond angle, bond type, and Mayer bond order (MBO). The bond length provides an indication of the intermolecular forces, with the longest bonds in the PMVE molecule being the C₂–O bond (1.359 Å) and the C₃–O bond (1.380 Å). Mayer bond order is commonly used to describe the relative strength of chemical bonds. The C₁=C₂ bond has the highest bond order of 1.694, indicating a strong interaction between the C₁ and C₂ atoms. In contrast, the C₂–O and C₃–O bonds have the smallest bond orders of 1.027 and 1.060, suggesting weak interactions between the C₂ and O atoms and the C₃ and O atoms. These weak interactions make the C₂–O and C₃–O bonds more susceptible to breaking under chemical reactions or high-temperature conditions, leading to the formation of radicals such as COF₃, C₂F₃, CF₃, and C₂F₃ (Figure 3).

3.1.2. Charge Distribution

The Fukui function, based on electron density, is commonly used to predict the reactivity of molecules. It reveals the sensitivity of specific points within a molecule to electron attack. The Fukui function is defined as follows:

$$f^{+}={\displaystyle \frac{({\rho }^{N+\delta }(r)-{\rho }^N(r))}{\delta }}$$

(3)

$$f^{-}={\displaystyle \frac{({\rho }^{N-\delta }(r)-{\rho }^N(r))}{\delta }}$$

(4)

where N denotes the number of electrons in the reference state of the molecule, and δ is the fraction of the electron [39]. Figure 4 demonstrates the values of Fukui functions mapped onto the surface of the electron density image.

In the case of a chemical reaction, the f⁺ function indicates regions that are more receptive to electrons and thus more susceptible to nucleophilic attack. As shown in Figure 4a, electrons are more readily acquired near the C₁=C₂ bond compared to other regions. For the f—function, the red region corresponds to areas where the electron density decreases, making them more vulnerable to electrophilic attack. From Figure 4b, it can be observed that the C₂–O and C₁–F₂ bond positions are more likely to lose electrons.

Based on the previous calculations of bond length and bond order, along with the current results, it is clear that the reactivity of the C₂–O and C₂–F₃ bonds is significantly higher than that of other sites. As a result, the initial cleavage of the PMVE molecule occurs at the C₂–O and C₂–F₃ bond positions.

3.2. Insulating Performance Analysis of PMVE/CO₂

During the gas discharge process, ionization, electron affinity, and electron transition play crucial roles [40]. Ionization energy and electron affinity together represent the binding strength of atoms to electrons. A higher ionization energy indicates a stronger atomic binding to electrons. Therefore, the gas is more resistant to breakdown. Excitation energy, however, reflects the energy required for a gas molecule to transition from the ground state to an excited state. By determining the excitation energy of molecules, the difficulty of gas discharge can be analyzed. To investigate the insulation properties of PMVE/CO₂, the ionization potential (IP), electron affinity (EA), and excitation energy (EX) of PMVE/CO₂ were calculated under different CO₂ content conditions. As shown in

Table 2. Ionization potential, electron affinity, and excitation energy of PMVE/CO₂.

CO2 Content	IP (eV)	EA (eV)	EX (eV)
0%	5.29	−0.42	5.16
30%	5.75	−1.28	5.06
40%	11.72	−0.85	5.03
50%	6.16	−2.27	5.06
60%	7.04	−2.43	5.10

, the ionization energy of the gas mixture is highest when the CO₂ content is 40%, followed by the mixture with 60% CO₂, while pure PMVE gas exhibits the lowest ionization energy. Furthermore, gas mixtures with varying CO₂ content do not exhibit electron affinity, and their excitation energies (EX) remain similar, indicating that the addition of CO₂ has little effect on the electron excitation process, which is almost negligible.

When the CO₂ content is 40%, the PMVE/CO₂ gas mixture exhibits significant electrical properties. At this mixing ratio, the ionization energy of the gas mixture is the highest, and its electron affinity is second only to that of pure PMVE gas, indicating that its atoms or molecules have the strongest electron-binding ability. This significantly enhances the insulation performance of the gas. Additionally, the excitation energy of gas mixtures with varying CO₂ content remains similar, suggesting that the addition of CO₂ has little effect on the electron excitation process. Based on a comprehensive analysis, the PMVE/CO₂ gas mixture achieves the best insulation performance at a CO₂ content of 40%, making the gas more resistant to breakdown.

3.3. Decomposition Process of PMVE/CO₂ Mixture

3.3.1. Effect of Temperature on the Decomposition Process

To further investigate the effect of temperature on the decomposition characteristics of PMVE, molecular dynamics simulations were conducted for the PMVE/CO₂ mixture system in the temperature range of 2200 K to 3200 K. Figure 5 illustrates the decomposition behavior of PMVE and CO₂ over this temperature range. The results show that the thermal decomposition rate of PMVE increases with temperature. At 2200 K, neither PMVE nor CO₂ undergoes significant decomposition. When the temperature rises to 2400 K, the decomposition rate remains slow, with only 8 PMVE molecules and 7 CO₂ molecules decomposing within the simulation time. As the temperature increases to 2800 K, the decomposition rate accelerates significantly, and the decomposition of both PMVE and CO₂ intensifies. By 3200 K, the decomposition reaction becomes even more pronounced, with 91 PMVE molecules decomposed by the end of the simulation, indicating that the decomposition of PMVE is nearly complete.

Figure 6 shows the variation in total potential energy of the PMVE/CO₂ system over time within the temperature range of 2200 K to 3200 K, revealing the energy characteristics during the decomposition reaction. At all temperatures, the total potential energy of the system increases over time, indicating that the decomposition of the PMVE/CO₂ mixture is an endothermic process, which aligns with real-world behavior. Below 2600 K, changes in potential energy are minimal, reflecting a low degree of decomposition and a relatively slow process. However, as the temperature rises to 2800 K, the potential energy increases more rapidly between 0 and 200 ps, signifying an acceleration in the decomposition of the gas mixture. At 3000 K, the potential energy rises sharply within the first 500 ps and stabilizes after 700 ps, indicating that the decomposition process is nearly complete. In summary, significant decomposition of the PMVE/CO₂ mixture mainly occurs at temperatures of 2800 K and above.

Figure 7 presents the distribution of the maximum quantities of PMVE/CO₂ decomposition products across the temperature range of 2200 K to 3200 K. The results show that the decomposition of the PMVE/CO₂ gas mixture primarily produces C₂F₂, COF₃, COF₂, F, C₂F₃, CO, CF₃, C₂F₃, and C₂F₄. Statistical analysis reveals that the overall number of decomposition products increases significantly with rising temperature. At 2200 K, the PMVE/CO₂ mixture shows minimal decomposition. Between 2200 K and 2800 K, the main decomposition products are C₂F₂, COF₃, F, and C₂F₃. As the temperature increases to 3000 K, the production of COF₂ begins to rise sharply. By 3200 K, the yields of CO and COF increase significantly, indicating more extensive decomposition.

Figure 8 illustrates the evolution of the quantity of each decomposition product over time at different temperatures. As the temperature increases, the decomposition rate of PMVE accelerates, and the yield of most decomposition products increases accordingly. Below 2400 K, the decomposition rate is extremely slow, with almost no decomposition occurring. However, at 2600 K, the decomposition process begins to accelerate, gradually forming COF₃, C₂F₃, and other products. When the temperature exceeds 2800 K, the decomposition of PMVE intensifies significantly, and the quantities of COF₂, COF, C₂F₂, and CO show a linear growth trend. At 3000 K, the formation rates of COF₃ slow down significantly at around 800 ps, indicating a saturation point. At 3200 K, the amount of COF₃ starts to decrease at 450 ps, suggesting that COF₃ redecomposes at high temperatures. Concurrently, the quantities of COF₂ and COF increase substantially, pointing to the correlation between the decrease in COF₃ and the formation of COF₂ and COF. Additionally, the quantities of F, C₂F₃, C₂F₃ and CF₃ first increase and then decrease significantly during the reaction. These fluctuations indicate the recombination and redecomposition of free radicals during PMVE decomposition. From a kinetic perspective, this reflects a dynamic equilibrium between the free radicals generated by PMVE decomposition, which helps maintain the insulation performance of the system to some extent. A small amount of C₂F₄ is produced during the reaction, aligning with experimental findings from previous studies [17], further confirming the reliability of the simulation.

3.3.2. Effect of CO₂ Content on the Decomposition Process

To compensate for the high liquefaction temperature of PMVE and enhance its insulation performance, insulating gases are often mixed with inert gases in engineering applications. In this section, ReaxFF-MD simulations are conducted for PMVE/CO₂ gas mixtures with CO₂ content of 30%, 40%, 50%, and 60% at 3000 K to investigate the effect of CO₂ content on the decomposition characteristics of the PMVE/CO₂ mixture. Figure 9 presents the time evolution of PMVE decomposition for different CO₂ contents at 3000 K. The results show that as the CO₂ content in the system increases, the decomposition process of PMVE intensifies. For instance, in the PMVE/CO₂ system with 60% CO₂, 74 PMVE molecules decompose, while only 37 PMVE molecules decompose in the 30% CO₂ system. This trend can be attributed to the increasing density of the gas mixture as PMVE content rises (as shown in Table 1). A denser mixture results in a higher number of molecules per unit volume, which increases the probability of effective molecular collisions, thereby accelerating the reaction.

From Figure 10 and Figure 11, a comparative analysis of product yields under different CO₂ concentrations reveals that the yields of COF₃, COF₂, and C₂F₂ increase linearly as the CO₂ content rises from 30% to 50%. However, when the CO₂ content reached 60%, the generation rate of these products began to show signs of saturation. Additionally, under the 60% CO₂ condition, the yields of CF₃, COF₃, and COF₂ were significantly higher compared to other mixtures. Notably, CO was only detected when the CO₂ content exceeded 50%. Furthermore, the quantities of C₂F₃ and CF₃ fluctuated dynamically over time at different mixing ratios. Overall, the trends in the formation of primary products across different CO₂ content conditions were consistent with those observed under varying temperature conditions.

3.4. Decomposition Mechanism of PMVE/CO₂

The analysis results in Section 3.3.1 and Section 3.3.2 show that changes in CO₂ content do not affect the decomposition mechanism of PMVE. To further elucidate the reaction mechanism of the PMVE/CO₂ mixture, the decomposition pathways and reaction enthalpy are presented in Figure 12 and

Table 3. Reaction pathways and reaction enthalpy, barrier of PMVE/CO₂ gas mixture.

No	Reaction Pathways	Reaction Enthalpy (KJ/mol)
A1	C3F6O → C2F3 + COF3	433.91
A2	C3F6O → C2OF3 + CF3	197.16
A3	C3F6O → C3F5O + F	488.14
B1	C2F3 → C2F2 + F	302.51
B2	C2F3 + F → C2F4	−506.77
B3	C2F3 + CF3 → C3F6	−431.58
C1	CF3 + F → CF4	−509.67
C2	2CF3 → C2F6	−372.48
D1	C3F5O → COF3 + C2F2	248.28
E1	COF3 → COF2 + F	93.90
E2	COF2 → COF + F	482.59
E3	COF → CO + F	155.29
F1	CO2 → CO + O	801.64

, respectively. The results reveal that the generation of certain products aligns with prior literature reports [14]. Specifically, three main cleavage pathways for PMVE have been identified. Among these, pathways A1 and A2 require less energy compared to pathway A3. The findings indicate that the C–O bond fracture occurs more easily than the C–F bond fracture during the initial decomposition of PMVE. Additionally, C₂F₃ transforms into C₂F₂ upon absorbing 302.51 kJ/mol of energy. Moreover, the B1 to C2 pathways are exothermic, suggesting that the formation of C₂F₄, C₃F₆, CF₄, and C₂F₆ is spontaneous. Previous experimental data have confirmed that the primary decomposition products of PMVE include C₂F₆, C₃F₆, C₃F₈, and CF₄ [17]. Therefore, the results obtained from the ReaxFF-MD simulation method are highly consistent with observed phenomena, validating the effectiveness and reliability of the simulation approach.

4. Conclusions

Based on density functional theory (DFT) and dynamic simulations, the electrical performance and decomposition characteristics of PMVE/CO₂ mixtures are studied theoretically. The effects of temperature and CO₂ content on the decomposition process are explored, revealing key insights into the decomposition behavior. The primary decomposition pathways of PMVE are identified, and the simulation results are further validated from a thermodynamic perspective. The conclusions are as follows:

(1) When the CO₂ content is 40%, the ionization energy of the gas mixture is highest, indicating that the system is most stable at this mixing ratio. Furthermore, gas mixtures with different CO₂ content do not exhibit electron affinity. The excitation energy of different content is similar, which indicates that the addition of CO₂ does not affect the electron excitation process.

(2) The primary cleavage of PMVE molecules during thermal decomposition predominantly occurs at the C₂–O and C–O bond positions, following three main cleavage pathways. The decomposition rate of the PMVE/CO₂ gas mixture increases significantly with rising temperature and CO₂ content, and the formation trends of the main decomposition products under different CO₂ content conditions are consistent with those observed under varying temperatures. Additionally, a dynamic equilibrium process involving free radicals occurs during PMVE decomposition, which helps maintain the insulation performance of the system.

(3) Compared with SF₆/CO₂, the PMVE/CO₂ mixture exhibits a significant advantage in terms of its extremely low global warming potential (GWP), which is less than one ten-thousandth of that of SF₆/CO₂, thereby contributing to a much smaller greenhouse effect under normal operating conditions. Furthermore, during the gas decomposition process, SF₆ produces highly toxic and corrosive by-products, particularly SO₂ and SOF₂, which pose greater environmental and safety hazards than those from PMVE. It is important to note that both gases can generate highly corrosive hydrogen fluoride (HF) when in contact with moisture. However, SF₆ demonstrates excellent equipment compatibility and is widely used in practice, whereas PMVE still faces challenges related to equipment compatibility before its large-scale application.