Study on the synergistic effect of thermal decomposition of binary ionic liquid mixtures

With the widespread application of binary ionic liquid (IL) mixtures in the chemical, energy, and environmental fields, improving their thermal stability has become crucial. This study three pyrrolidine-based pure ionic liquids (ILs) were selected to form two types of binary IL mixtures, including [Py₁₄][NTf₂]_(x)[Py₁₄][BF₄]_(10-x), and [Py₁₂][NTf₂]_(x)[BF₄]_(10-x). The thermal decomposition properties of the two mixtures were investigated and compared through thermogravimetric Fourier transform infrared spectroscopy (TG-FTIR), density functional theory (DFT), and molecular dynamics (MD) simulations. The TG results indicate that [Py₁₄][NTf₂]_(x)[Py₁₄][BF₄]_(10-x) exhibits higher thermal stability, and both IL mixtures demonstrate synergistic thermal decomposition behavior at different molar ratios. DFT analysis indicates that, compared to [NTf₂]^-, [BF₄]^- exhibits a stronger tendency to bind with cations, facilitating the formation of stable ionic clusters and enhancing overall stability. Additionally, hydrogen bonding interactions are widely present. While C₂-H is the main hydrogen bond donor, C₄-H, C₅-H, and even the hydrogen atom on alkyl can also be involved in hydrogen bonding, albeit as a weak donor. MD simulations reveal that the interactions between anions and cations are not directly correlated with the number of hydrogen bonds, nor do their trends exhibit a significant relationship with the interactions of the mixtures during thermal decomposition. The results will be helpful to select and design the ILs at high temperature, and contribute to their safety.