Experimental investigation of thermo-physical properties of geminal dicationic ionic compounds for latent thermal energy storage

Abstract To enhance thermal stability of ionic compounds and increase thermal storage density, a series of geminal dicationic ionic compounds have been synthesized. The structures of these geminal dicationic ionic compounds were confirmed by 1H NMR and 13C NMR. Besides, thermal stability was determined by thermogravimetric analysis (TGA); melting point, heat of fusion and heat capacity were investigated by differential scanning calorimetry (DSC) for synthetic geminal dicationic ionic compounds. The effects of alkyl side-chain, the H atom at position 2 of the imidazolium ring, and anions on the thermal properties of the geminal dicationic ionic compounds were investigated. Hydrogen bonding in geminal dicationic ionic compounds was studied, in the case of C4(mim)2(Br)2, by single-crystal X-ray diffraction. The thermal analysis results indicate that geminal dicationic ionic compounds show excellent thermal stability. The decomposition temperatures of geminal dicationic ionic compounds can be up to 741.25 K, and the latent heat can reach 115.69 kJ kg−1. It is increased on average by 61.8% and 126.1%, respectively, as compared to alkyl chain ionic compounds (C4mim)Br. It can be expected that these geminal dicationic ionic compounds are suitable for thermal storage applications. Enhanced thermal storage density can thus be achieved by increasing the density and heat capacity. These values are higher than that of the monocationic ionic compounds. It can be expected that these geminal dicationic ionic compounds are suitable for thermal storage applications.