To
enhance the thermal stability of ionic liquids (ILs) and increase
the latent heat, the effect of amount of hydrogen bonds for geminal
dicationic ionic liquids (DILs) was investigated and compared to that
of monocationic analogues. A series of geminal dicationic ionic liquids
with alkyl chain or electronegativity functional groups in the imidazolium
were synthesized. Thermal stability was determined by TGA; melting
point, heat of fusion, and heat capacity were investigated by DSC
for synthetic DILs. The effect of molecular structure on the heat
of fusion was examined by changes alkyl side-chain, linkage chain,
C2–H of imidazole ring, and functional groups. Hydrogen bonding
in DILs was studied, in the case of C<sub>2</sub>(eim)<sub>2</sub>(Br)<sub>2</sub>, by single-crystal X-ray diffraction. The thermal
analysis results indicate that functionalized geminal dicationic ionic
liquids show excellent thermal stability. The decomposition temperatures
of geminal dicationic ionic liquids can be up to 603.74 K, and the
latent heat can reach 159.35 J g<sup>–1</sup>. It is increased
on average by 64.5% and 212.5%, respectively, as compared to alkyl
chain ionic liquid (C<sub>4</sub>mim)Br. It can be expected that these
geminal dicationic ionic liquids are suitable for thermal storage
applications
