Thermophysical properties of dicationic imidazolium-based ionic compounds for thermal storage

In order to improve the thermal stability of ionic liquids and enhance the thermal storage density, a series of dicationic ionic compounds containing incorporated Br ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , NTf ₂ ⁻ anions were synthesized. The structures of these dicationic ionic compounds were confirmed by ¹ H NMR, ¹³ C NMR and FT-IR. The dicationic ionic compounds’ thermo-physical properties were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect of molecular configuration on the heat of fusion was studied by changes alkyl side-chain, linkage chain, molecular structure symmetry, and anions. The quantum calculation was carried to validate the number of hydrogen bonds for the dicationic ionic compounds. The results showed that hydrogen bonds significantly increased compared to that of the monocationic ionic liquids (MILs). The thermal analysis results indicate that dicationic ionic compounds exhibit excellent thermal stability; the decomposition temperatures higher than 560 K; the melting points and heat of fusion value reached 481 K and 116.26 kJ·kg ⁻¹ , respectively. These values are higher than those of the MILs.