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. 2025 Mar 20;10(12):12645–12652. doi: 10.1021/acsomega.5c00788

A Kinetic Study of the Inhibition Mechanism of 1,1,1,3,3,3-Hexafluoropropane (HFC-236fa) on Hydrogen Combustion

Wei He †,‡,§, Qichun Zhang ‡,§, Cheng Wang ‡,§, Tao Ye †, Yan Li ‡,§, Kang Shen ‡,§,∥,*
PMCID: PMC11966246  PMID: 40191349

Abstract

graphic file with name ao5c00788_0008.jpg

HFC-236fa (1,1,1,3,3,3-hexafluoropropane) is regarded as a potential fire extinguishing alternative to halon, and the present study delves into its mechanism in hydrogen combustion suppression. Based on the master equation solved by the transition state theory, the reaction kinetics of HFC-236fa were analyzed, revealing that it tends to undergo heat-absorbing reactions when dissociating into smaller species. The study focuses on the key roles of hydrogen atoms (H) and hydroxyl radicals (OH) in the radical scavenging reaction. The results show that the differences in the rate constant of the unimolecular dissociation and intramolecular elimination reactions of HFC-236fa are significant at low temperatures, and the differences gradually decrease with increasing temperatures. The reaction generating CF3CHCF2 and HF was the fastest rate reaction channel, suggesting that it plays an important role in combustion inhibition. Overall, the combustion inhibition mechanism of HFC-236fa is mainly dominated by the H-abstraction reaction of the OH in the carbon center, while the trifluoromethyl-related reaction contributes little to the inhibition. This study provides an important theoretical basis for the design and evaluation of fire extinguishing agents.

1. Introduction

Hydrogen, as an ideal energy carrier for the future, has the advantages of high energy density, clean combustion and wide application potential.1−3 However, due to its high diffusivity and low ignition energy, hydrogen poses an explosion risk in practical applications, especially in environments such as hydrogen refueling stations, where hydrogen leaks can easily cause explosions when mixed with air.4,5 Therefore, the key to ensuring the safe use of hydrogen energy lies in the research and application of effective flame suppressants.6,7

Halon fire suppressants, particularly CF3Br (1301), are widely recognized for their excellent fire suppression properties.8 At one time, CF3Br accounted for 80% of the cargo-bay fire extinguishing agent market. However, given its significant ozone depletion potential, the production of CF3Br has been phased out, a shift that stems from the relevant provisions of the 1987 Montreal Protocol.9 This change has prompted researchers to actively search for effective halon alternatives to meet fire suppression needs. HFC-236fa (1,1,1,3,3,3-hexafluoropropane) suppresses ignition by absorbing heat and interrupting chemical reactions in the flame. Environmentally, it has a Global Warming Potential (GWP) of 1060 and an Ozone Depletion Potential (ODP) of 0. It does not destroy the ozone layer and has an atmospheric lifetime of about 9.3 years. Acute toxicity is low, and prolonged exposure may cause mild dizziness or nausea. In the environment, HFC-236fa is not readily biodegradable, but its persistence is low, and its impact is relatively small.

The flame suppression mechanism of HFC-236fa is closely related to its molecular structure and consists of three main aspects: (a) scavenging reactive radicals through chemical reactions to slow down or interrupt the combustion chain reaction; (b) acting as a chemical heat sink to reduce the temperature generated by the dissociation of the inhibitor; and (c) generating physical heat through a phase transition or sensible heat effect to further suppress the flame.10−12

The current study will focus on the first two inhibition mechanisms of HFC-236fa, particularly the effects triggered by the primary reaction. The free radical scavenging ability of HFC-236fa is assessed by investigating the bimolecular reaction of the inhibitor with H and OH as a prototypical reaction, while the chemical heat sink effect is reflected in the tendency of the inhibitor to undergo a heat-absorbing reaction in the initial phase. Therefore, an in-depth investigation of the fundamental combustion chemistry of HFC-236fa, especially its decomposition behavior and reaction competition with H/OH radicals, is essential for understanding its inhibitory role in hydrogen combustion and providing theoretical support for the design of novel fire extinguishing agents.

Tan et al.13 investigated the thermal decomposition characteristics of HFC-236fa as a clean gas extinguishing agent. The results showed that HFC-236fa decomposed gradually in the temperature range from 500 to 750 °C. The decomposition of HFC-236fa was stable at 500 °C, and started to decompose slightly at 600 °C. It remained stable at 500 °C, started to decompose slightly at 600 °C, and decomposed violently at 750 °C. The decomposition of HFC-236fa was also found to be stable at 500 °C, and the decomposition of HFC-236fa was found to be stable at 600 °C. Decomposition products such as hydrogen fluoride (HF) and pentafluoropropene (C3HF5) were detected by GC, FTIR and GC-MS.

Wang et al.14 studied the pyrolysis characteristics and decomposition mechanism of HFC-236fa extinguishing agent. It was shown that the pyrolysis of HFC-236fa occurred in the range of 500 to 850 °C. It remained stable below 600 °C, and started to decompose above this temperature, and the decomposition intensified as the temperature increased, with a significant decrease in concentration at 850 °C. The decomposition of HFC-236fa was also detected by GC, IC and GC-MS analyses. Pyrolysis products such as CHF3, CF2=CHF, CF3C≡CCF3 and (CF3)2C=CF2 were detected by GC, IC and GC-MS analyses. In addition, based on the density functional theory (DFT), the study proposed the decomposition mechanism of HFC-236fa and obtained detailed information on the activation energy and dissociation pathway. Pan et al.15 presented an equation of state for HFC-236fa covering the temperature range from the triple-phase point (179.6 K) to 400 K and the pressure range below 70 MPa. The equation can be used to calculate the thermodynamic properties of HFC-236fa such as density, specific heat capacity, enthalpy and entropy. In addition, the study provided data on liquid viscosity and thermal conductivity, which were validated against an existing database of thermophysical properties.

Wang et al.16 revealed the reaction pathway of HFC-227ea at high temperatures through a combination of theoretical calculations and experimental data, and calculated the reaction rate constants under different temperature and pressure conditions. It is shown that HFC-227ea effectively slows down the combustion process by reacting with the key free radicals (e.g., hydrogen atoms and hydroxyl radicals) in the hydrogen combustion process and inhibiting the generation of these free radicals.

The primary goal of this study is to establish the basic reaction mechanisms characterizing the inhibition kinetics of HFC-236fa in hydrogen combustion. The study is centered around two key components: (1) the construction of a potential energy surface for the decomposition of HFC-236fa and its reactions with H and OH; and (2) the calculation of rate constants for the relevant reactions at different temperatures and pressures.

2. Theoretical and Computational Methods

2.1. Electronic Structure Methods

Geometry optimization, zero-point energy and frequency analysis of all stationary points on the HFC-236fa potential energy surface using the B3LYP/6–311G(2df, p) method.17−20 This is verified by inspection of the hindered rotor potential to ensure that the geometry of the stationary point on the potential energy surface is the lowest energy structure. Transition states were identified by having one and only one imaginary frequency and verified by vibrational modes to correspond to the desired response coordinates. For uncertainty, intrinsic reaction coordinate analysis was performed to ensure that the transition state was connected to the indicated reactants and products. The more accurate relative energies of these species were obtained at the G4 (0 K) level, which guarantees an energy precision within the range of approximately 1 kcal·mol–1.21 All density functional calculations were performed using the Gaussian 09 program.22

2.2. Reaction Kinetics

The temperature- and pressure-dependent rate constants for the corresponding reactions on the potential energy surface are calculated by solving the master equation based on the transition state theory and the Rice–Ramsperger–Kassel–Marcus theory with the Eckart tunneling effect correction via the MESS program.23−25 Mess programs have been developed to deal with complex systems including multipotential wells and multireaction channels to obtain temperature- and pressure-dependent rate coefficients.

The traditional transition state theory is used to predict rate constants for reactions with significant energy barriers. The torsional motion of species and transition states treated with a one-dimensional hindered rotor is employed. Relaxation scans along dihedral coordinates at 10° intervals at the B3LYP/6–311G(2df, p) level were obtained for the hindered potential of the internal rotors. For the dissociated channel with no barrier, the rate constants were calculated using variational transition state theory. Due to the small rotational potential barrier, the torsional modes involved in the configuration of the transition state region were treated with a one-dimensional free rotor.

The interaction between the reactants and the bath gas Ar is represented by the Lennard–Jones (L–J) collision model. The L–J parameters for Ar are σ = 3.47 Å and ε = 79.2 cm–1, respectively.26,27 It was calculated using Joback’s group contribution scheme28,29 for the HFC-236fa molecule with σ = 5.2 Å and ε = 211.42 cm–1.The collision energy transfer probability is usually approximated using a single-exponential down model, i.e., < △Edown > = 200*(T/300)0.75 cm–1.30

3. Results and Discussion

In the following section, the reaction kinetics of the initial decomposition of HFC-236fa and its reaction with H/OH radicals will be described in detail. The molecular structure in Figure 1 shows that HFC-236fa contains two symmetrically equivalent trifluoromethyl groups and two symmetrical H atoms attached to one methylene group.

Figure 1.

Figure 1

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Optimized geometry of HFC-236fa at B3LYP/6–311G(2df, p) level in Å.

3.1. Unimolecular Decomposition of HFC-227ea

3.1.1. Potential Energy Surface

The effectiveness of inhibitors is significantly influenced by their chemical heat sink. In this study, the primary focus is on the tendency of the inhibitor to undergo endothermic reactions during the initial stage of hydrogen combustion involving HFC-236fa. The initial decomposition of HFC-236fa can take place through several reaction channels. Seven single-molecule decomposition channels were identified, including three simple bond fission reactions (R1-R3) and four elimination reactions (R4-R7).

Figure 2 shows the potential energy surface (PES) of the relevant reactions during the initial decomposition of HFC-236fa. Among the three simple bond fission reactions of HFC-236fa, C–C bond fission to form 2,2,2-trifluoroethyl (CF3CH2) and trifluoromethyl (CF3) has the lowest bond dissociation energy of 95.3 kcal·mol–1 (R1). The fission of H atoms on the methylene group of HFC-236fa produces 1,1,1-trifluoro-3λ1-propan-2-yl (CF3CHCF3) and H with a bond dissociation energy of 101.9 kcal·mol–1 (R2). In addition, in the C–F bond fission reaction of HFC-236fa, the bond dissociation energy of the 1,1-difluoro-3λ1-propyl (CF3CH2CF2) and F atoms is 122.7 kcal·mol–1 (R3). In HFC-236fa, the dissociation energy of the C–H single bond is about 7 kcal·mol–1 higher than that of the C–C bond, while the dissociation energy of the C–F bond is the largest among the three reaction channels, which indicates that the C–F bond has a lower reactivity during the initial pyrolysis of HFC-227ea.

Figure 2.

Figure 2

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Potential energy surfaces for the main unimolecular decomposition pathways of HFC-236fa were calculated at the G4 level. The unit is in kcal·mol–1.

Among the four molecular elimination pathways of HFC-236fa, the 1,2-HF elimination reaction from the central and terminal carbons will occur at the lowest energy barrier of 70.9 kcal·mol–1 to produce 1,1,3,3,3-pentafluoroprop-1-ene (CF3CH=CF2) and HF (R4). Wang et al.16 calculated an energy barrier of 77.5 kcal·mol–1 for the 1,2-HF elimination reaction of HFC-227ea from the central and terminal carbons, suggesting that HFC-236fa is more reactive than HFC-227ea. The transfer of HFC-236fa H atoms from the central C to the terminal C occurs at an energy barrier of 112.8 kcal·mol–1 (R5), yielding 1,1,1-trifluoro-2λ2-ethane (CF3CH) and fluoroform (HCF3). The transfer of fluorine atoms from the terminal carbon to the central carbon atom in HFC-236fa has an activation energy of 123.9 kcal·mol–1 (R6), resulting in the products 1,1,1,2-tetrafluoroethane (CF3C(F)H2) and difluoro-λ2-methane (CF2). The energy barrier for this reaction is the next highest, after that of the central methylene elimination reaction, suggesting that this reaction is also less competitive and difficult to occur under conventional conditions. The reaction activation energy of HFC-236fa in the elimination reaction of the central methylene group was as high as 177.2 kcal·mol–1, indicating that the reaction is difficult to occur under conventional conditions, and thus the direct production of perfluoroethane (F3CCF3) and CH2 is highly unlikely (R7).

3.2. Bimolecular Reaction of HFC-236fa + OH

The two most representative radicals, H and OH, in hydrogen combustion were selected to investigate the kinetic mechanisms of chemical scavenging by HFC-236fa. The potential energy surface (PES) for the bimolecular reaction between HFC-236fa and OH is shown in Figure 3. Figure 3 shows the potential energy surface (PES) of all possible pathways involved in the reaction of OH with HFC-236fa, including the abstraction of H atoms (R8 and R9) as well as radical substitution (R10).

Figure 3.

Figure 3

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Potential energy surface for the H-abstraction reaction of HFC-236fa with OH was calculated at the G4 level. The unit is in kcal·mol–1.

In the H-abstraction pathway of HFC-236fa, the hydroxyl group abstracts the H atoms on the methylene group at a minimum barrier of 3.8 kcal·mol–1 (TS6) to produce products 1,1,1-trifluoro-3λ1-propan-2-yl (CF3CHCF3) and H2O (R8). This reaction is exothermic, releasing energy up to – 15.1 kcal·mol–1. Similarly, the lowest energy barrier H-abstraction reaction path of the hydroxyl group in HFC-236fa has a lower energy barrier and releases more energy than the radical H-abstraction reaction path of HFC-227ea.16 The abstraction of the F atom from the trifluoromethyl radical by the hydroxyl group occurs at the highest energy barrier of 75.4 kcal·mol–1 (TS5), yielding products 1,1-difluoro-3λ1-propyl (CF2CH2CF3) and HOF (R9), indicative of the more difficult products of this reaction pathway. Due to the high stability and low reactivity of the C–F bond, the abstraction reaction of fluorine atoms needs to overcome a significantly higher energy barrier, which is significantly higher for TS5 than for TS6.

In HFC-236fa, the substitution of hydroxyl groups for F atoms on the trifluoromethyl radical requires overcoming an energy barrier of 65.5 kcal·mol–1 (TS7) to produce products 1,1-difluoro-3λ1-propan-1-ol (F2C(OH)CH2CF3) and F (R10). In HFC-236fa, the F atom on the hydroxyl-substituted trifluoromethyl radical needs to overcome a higher energy barrier. Comparing TS7 (substitution reaction, 65.5 kcal·mol–1) with TS6 (H-abstraction reaction, 3.8 kcal·mol–1), the H-abstraction pathway is more feasible. This suggests that in HFC-236fa the hydroxyl group is more inclined to participate in the H-abstraction reaction than in the F substitution reaction.

3.3. Bimolecular Reaction of HFC-236fa + H

The potential energy surface (PES) for the abstraction and substitution reactions between HFC-236fa and H is shown on the right side of Figure 4. Similar to the reactions of HFC-236fa with OH, the figure illustrates three abstraction pathways and two substitution pathways.

Figure 4.

Figure 4

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Potential energy surface for the H-abstraction reaction of HFC-236fa with H was calculated at the G4 level. The unit is in kcal·mol–1.

In the H-abstraction reaction pathway of HFC-236fa, H atoms are abstracted from the methylene group at a minimum energy barrier of 114 kcal·mol–1 (TS9) to produce 1,1,1-trifluoro-3l1-propan-2-yl (CF3CHCF3) and H2 (R11). The energy barrier for this reaction is very similar to the hydrogen atom extraction reaction on the carbon center of HFC-227ea.16

The abstraction of the fluorine atom from the trifluoromethyl radical by the hydrogen atom must overcome an energy barrier of 36.1 kcal·mol–1 (TS8) to produce 1,1-difluoro-3λ1-propyl (CF2CH2CF3) and HF (R12). This energy barrier is lower than that of the hydroxyl abstraction pathway (TS5, 75.4 kcal·mol–1), but still higher than that of the H-abstraction reaction at the methylene site (TS9, 11.4 kcal·mol–1).

In HFC-236fa, the substitution of a hydrogen atom for a fluorine atom on the trifluoromethyl radical overcomes an energy barrier of 58.6 kcal·mol–1 (TS10) to yield products 1,1-difluoro-3λ1-propane and F (R13). This energy barrier is lower than that of the hydroxyl substitution pathway (TS7, 65.5 kcal·mol–1) but significantly higher than that of hydrogen abstraction reactions (e.g., TS6, 3.8 kcal·mol–1 and TS9, 11.4 kcal·mol–1). Thus, the H-substitution pathway is thermodynamically unfavorable and difficult to occur significantly under conventional conditions.

3.4. Temperature- and Pressure-Dependent Rate Coefficients

To gain insight into the effect of different reaction pathways of HFC-236fa on the inhibition of hydrogen combustion, the rate constant on the potential energy surfaces of unimolecular dissociation, H-abstraction, OH-abstraction, H substitution, and OH substitution of HFC-236fa were calculated by solving the master equation.

The calculations cover the temperature range from 200 to 2000 K and the pressure range from 0.01 to 100 atom. In addition, the modified Arrhenius parameters for the rate constants are detailed in Table 1.

Table 1. Rate Constants for HFC-236fa, k = ATnexp (−Ea/RT). Units Are in cm3, s, and cal·mol–1.

reactions A n Ea pressure (atom)
R1 CF3CH2CF3=CF3CH2 + CF3
  1.75 × 1043 –8.78 86,333.79 0.01
  1.01 × 1038 –7.11 84,810.01 0.039
  2.66 × 1034 –5.98 83,717.65 0.1
  9.45 × 1025 –3.35 80,991.02 1
  1.34 × 1019 –1.23 78,637.25 10
  8.84 × 1014 0.05 77,126.95 100
R2 CF3CH2CF3=CF3CHCF3 + H
  1.28 × 1028 –4.31 91,425.97 0.01
  4.03 × 1023 –2.92 89,916.64 0.039
  8.54 × 1020 –2.09 88,995.15 0.1
  1.04 × 1016 –0.58 87,245.10 1
  6.04 × 1013 0.10 86,417.73 10
  2.07 × 1013 0.24 86,241.97 100
R3 CF3CH2CF3=CF3CH2CF2 + F
  1.62 × 1025 –3.34 97,514.01 0.01
  7.18 × 1020 –1.99 96,049.34 0.039
  1.83 × 1018 –1.19 95,153.18 0.1
  2.54 × 1013 0.30 93,421.30 1
  1.16 × 1011 1.01 92,554.11 10
  3.49 × 1010 1.17 92,356.38 100
R4 CF3CH2CF3=CF3CHCF2 + HF
  3.14 × 1010 0.38 63,093.07 0.01
  1.78 × 1005 2.03 61,437.16 0.039
  7.53 × 1001 3.08 60,330.91 0.1
  6.08 × 10–06 5.27 57,902.20 1
  2.52 × 10–10 6.61 56,323.02 10
  8.11 × 10–12 7.07 55,766.76 100
R5 CF3CH2CF3=CF3CH + HCF3
  6.46 × 1026 –3.35 124,582.95 0.01
  1.13 × 1023 –2.18 123,304.98 0.039
  6.86 × 1020 –1.50 122,533.82 0.1
  5.10 × 1016 –0.24 121,054.80 1
  4.48 × 1014 0.39 120,290.78 10
  1.41 × 1014 0.54 120,100.74 100
R6 CF3CH2CF3=CF3CF(H2) + CF2
  7.63 × 1014 –0.19 125,359.53 0.01
  1.88 × 1013 0.30 124,768.11 0.039
  3.91 × 1012 0.51 124,512.31 0.1
  8.90 × 1011 0.70 124,268.95 1
  7.31 × 1011 0.73 124,236.40 10
  7.17 × 1011 0.73 124,233.01 100
R7 CF3CH2CF3=CF3CF3 + CH2
  2.49 × 1010 1.12 177,675.83 0.01
  2.33 × 1010 1.13 177,665.07 0.039
  2.30 × 1010 1.13 177,662.83 0.1
  2.28 × 1010 1.13 177,661.50 1
  2.28 × 1010 1.13 177,661.37 10
  2.28 × 1010 1.13 177,661.35 100
R8 CF3CH2CF3 + OH=CF3CH2CF2 + HOF
  1.40 × 1006 2.58 75,231.07  
R9 CF3CH2CF3 + OH=CF3CHCF3 + H2O
  5.79 × 10–01 3.93 423.84  
R10 CF3CH2CF3 + OH=CF3CH2CF2(OH) + F
  3.48 × 10–30 12.46 47,352.27  
R11 CF3CH2CF3 + H=CF3CH2CF2 + HF
  1.64 × 10–21 10.17 4537.64  
R12 CF3CH2CF3 + H=CF3CHCF3 + H2
  1.66 × 1001 2.81 6526.77  
R13 CF3CH2CF3 + H=CF3CH2CF2(H) + F
  4.05 × 10–15 8.25 45,214.19  
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3.4.1. Unimolecular Dissociation and Intramolecular Elimination Reactions of HFC-236fa

The rate constant for the single molecule dissociation reaction and the intramolecular elimination reaction of HFC-236fa are illustrated in Figure 5. The rate constants for the single-molecule dissociation and intramolecular elimination reactions of HFC-236fa at two different pressures show a clear temperature dependence. The differences in rate constants of the reaction channels were large at temperatures below 1000 K, but the differences in the reaction rate constants gradually decreased as the temperature increased to 1800 K. The rate constants of the reaction channels were also found to be very different from those of the reaction channels. The HFC-236fa intramolecular elimination reaction to generate CF3CHCF2 and HF (R4) is the reaction channel with the fastest rate, which suggests that CF3CHCF2 and HF are the major products in the inhibited combustion process.

Figure 5.

Figure 5

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Rate constants for unimolecular dissociation and intramolecular decomposition of HFC-236fa. (a) p = 0.01 atom; (b) p = 100 atom.

Second, the rate constant for the HFC-236fa unimolecular dissociation reaction (R1) to produce CF3+CF3CH2 is close to that of the R4 reaction at temperatures above 400 K, suggesting that this reaction is also the dominant reaction path.

In addition, the rate constants for the HFC-236fa unimolecular dissociation reactions R3 and R2 are second only to R1 and R4, and they gradually approach those of R1 and R4 as the temperature increases. In contrast, the rate constant for the HFC-236fa unimolecular dissociation reaction R7 to produce CH2 + CF3CF3 is significantly lower than the other reaction channels, suggesting that this reaction is at a competitive disadvantage and is less likely to occur.

In addition, the rate constants of reactions R5 and R6 are smaller than those of R1, R2, R3, and R4 at temperatures lower than 1000 K. However, the difference between the rate constants decreases as the temperature increases, and especially at high temperatures, the difference in the rate constants becomes smaller and smaller. This trend suggests that although the reaction rates of these reaction channels are slower at low temperatures, they gradually approach those of the other major reaction channels at high temperatures.

3.4.2. OH-Abstraction and Substitution Reaction Rate Constants for HFC-236fa

As shown in Figure 6, the reaction properties of HFC-236fa indicate that the hydroxyl H-abstraction reaction at the carbon center, which has the highest rate constant (R8), is the dominant reaction pathway and plays a key role in the inhibition of hydrogen combustion.

Figure 6.

Figure 6

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Rate constants for the H-abstraction reaction of HFC-236fa with OH at temperatures from 300 to 1500 K.

In contrast, the hydroxyl abstraction reaction of the F atom in trifluoromethyl has the lowest rate constant and very low kinetic activity (R9). At temperatures above 1000 K, the rate constant for hydroxyl abstraction and substitution reactions in trifluoromethyl converge, but both are still significantly lower than the rate of H-abstraction from the hydroxyl group at the carbon center. This suggests that the effect of trifluoromethyl and hydroxyl-related reactions on combustion inhibition is negligible. Overall, the combustion inhibition mechanism of HFC-236fa is dominated by the carbon-centered hydroxyl H-abstraction pathway, while the abstraction and substitution reactions in the trifluoromethyl group are not kinetically or thermodynamically significantly competitive.

3.4.3. H-Abstraction and Substitution Reaction Rate Constants for HFC-236fa

Figure 7 shows that the reaction of HFC-236fa is most active with the largest rate constant for H-abstraction by the H atom in the carbon center (R11), followed by the rate of H-abstraction by the F atom in the trifluoromethyl radical (R12). In contrast, the rate constant of the substitution reaction of the F atom in the trifluoromethyl radical (R13) is much smaller than that of the H-abstraction reaction, indicating that the substitution reaction is not kinetically competitive. This suggests that the reaction of HFC-236fa mainly proceeds through the H-abstraction pathway, especially the carbon-centered H-abstraction reaction is dominant, while the substitution reaction plays a negligible role in the combustion inhibition mechanism.

Figure 7.

Figure 7

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Rate constants for the H-abstraction reaction of HFC-236fa with H at temperatures from 300 to 1500 K.

4. Conclusions

In this study, the inhibition mechanism of HFC-236fa on hydrogen combustion is explored in detail based on the master equation solved by transition state theory. The study analyses the single-molecule decomposition chemistry of HFC-236fa and explores its tendency to undergo endothermic reactions when dissociating into smaller species. To reveal the chemical kinetics of HFC-236fa in radical scavenging reactions, two key reactive radicals were focused on: hydrogen atoms (H) and hydroxyl radicals (OH). The results show significant differences in the rate constant of the unimolecular dissociation and intramolecular elimination reactions of HFC-236fa at low temperatures, which gradually decrease with increasing temperature. The reaction generating CF3CHCF2 and HF (R4) is the fastest reaction channel, and the major products indicate that it plays an important role in inhibiting the combustion process. The combustion inhibition mechanism of HFC-236fa is primarily driven by the carbon-centered hydroxyl H-abstraction reaction, while the trifluoromethyl group reactions have negligible kinetic and thermodynamic significance. The hydrogen combustion inhibition mechanism of HFC-236fa is mainly dominated by the abstraction reaction between the hydroxyl group of the carbon center and the hydrogen atom, which plays a decisive role. In contrast, reactions involving trifluoromethyl groups, such as substitution and abstraction reactions of trifluoromethyl radicals, make a negligible contribution to the overall combustion inhibition due to their significantly smaller rate constants and limited kinetic and thermodynamic effects. This research emphasizes the key role of HFC-236fa in scavenging free radicals and suggests that the mechanism and role of the inhibitor in reacting with other reactive radicals should be further explored.

Acknowledgments

This work was supported by the Guangxi Natural Science Foundation 2025GXNSFHA069066; Liuzhou Science and Technology Programme Project “Research on the Development of Waste Lithium Battery Intelligent Dumping Technology” (Project No. Liukeji (2024) 57 2024PA0101A011).

The authors declare no competing financial interest.

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