Hydrogen storage in organosilicon ionic liquids

New structures of ionic liquids have been studied as liquid organic hydrogen carriers. The hydrogenation of organosilicon compounds containing a carbazole fragment was carried out for the first time. The N–(CH2)3–Si fragment in the composition of the hydrogen carrier based on organosilicon moieties was found to be more suitable than the N–CH2–Si bond. Ionic liquids with a carbazole fragment containing silicon atoms were synthesized for the first time. It was possible to significantly reduce the melting point of such ionic liquids by introducing an organosilicon linker between carbazole nitrogen and imidazolium ion. The synthesized ionic liquid is a liquid at room temperature. Hydrogenation-dehydrogenation experiments demonstrated that such ionic liquids are thermally stable up to at least 220 °C, and nearly quantitative conversion can be achieved. Both the hydrogenation and dehydrogenation processes were carried out using the same Pd/C catalyst. The theoretical total gravimetric hydrogen capacities for synthesized ionic liquids are 2.05% and 1.58%.