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

Abstract

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 BH₄⁻ 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.