Deep Eutectic Solvents Formed by Complex Hydrides: A New Class of Hydrogen-Rich Liquid.

Deep eutectic solvents (DESs) are novel mixtures that exhibit a significant depression in melting points compared to their individual components. This work finds that combining tetrabutylammonium borohydride (TBABH) with ammonia borane (AB) yields new, stable, hydrogen-rich liquids under ambient conditions, with a glass transition as low as -50 °C. Liquid mixtures containing up to 6.9 wt% hydrogen can be easily obtained through physical grinding. The strong interaction between the BH anion of TBABH and AB coupled with the vibration dynamics of the alkyl chains accounts for the sharp decrease in melting point. The eutectic point is identified at a TBABH-AB molar ratio of 1-2. Increasing the AB ratio further reduces the glass transition temperature but also induces a cold crystallization phenomenon. These mixtures can release hydrogen at temperatures as low as 60 °C, making them promising candidates for hydrogen storage. This represents the first example of a hydride-based DES, advancing research on complex hydrides and opening the door to the discovery of new hydrogen-rich liquids for various applications.