The inhibition mechanism of thermal decomposition of binary ionic liquid mixtures by TG-FTIR and DFT methods

Binary ionic liquid (IL) mixtures are widely used in chemical, electrochemical sensors and energy storage. Researchers obtain the ideal binary IL mixtures by adjusting the type and molar ratio of the parent salt ILs. In fact, IL mixtures will occur flammable gas or toxic gas due to thermal decomposition. Therefore, it is necessary to study the thermal decomposition process and thermal decomposition interaction of binary IL mixtures. In this work, [Bmim][BF₄]_(x)[OTf]_(10−x) and [Py₁₄][NTf₂]_(x)[Bmim][OTf]_(10−x) were selected as a research object. Comparative studies have demonstrated that the mixtures of [Bmim][BF₄]_(x)[OTf]_(10−x) significantly exhibit an inhibitory effect on thermal decomposition. Thermogravimetric fourier infrared spectroscopy (TG-FTIR) and density functional theory (DFT) were used to study the thermal decomposition mechanisms and interactions of this mixtures. TG experiments revealed that the thermal stability of the mixtures showed suppression of their thermal decomposition temperatures at a molar ratio of 9:1. In order to further analyze the thermal decomposition mechanism, the reaction sites and interaction energies of the binary ionic liquid mixtures were analyzed by using the DFT theoretical approach. By analyzing the electrostatic potential (ESP) distribution on the surface of ILs, it is found that the most probable sites of interaction are C₂–H, F and O atoms. It is concluded that [BF₄]⁻ is more suitable as electron donor than [OTf]⁻. The interaction between anion and cation in the [Bmim][BF₄] complex is stronger than in the [Bmim][OTf]. The integrated experimental and theoretical methods can deeply understand the interaction mechanism of binary IL mixtures during the thermal decomposition process, which will promote its safe use.