Improved hydrogen-storage thermodynamics and kinetics for an RbF-doped Mg(NH2)2-2 LiH system.

The introduction of RbF into the Mg(NH2)2-2 LiH system significantly decreased its (de-)hydrogenation temperatures and enhanced its hydrogen-storage kinetics. The Mg(NH2)2-2 LiH-0.08 RbF composite exhibits the optimal hydrogen-storage properties as it could reversibly store approximately 4.76 wt % hydrogen through a two-stage reaction with the onset temperatures of 80 °C for dehydrogenation and 55 °C for hydrogenation. At 130 °C, approximately 70 % of hydrogen was rapidly released from the 0.08 RbF-doped sample within 180 min, and the fully dehydrogenated sample could absorb approximately 4.8 wt % of hydrogen at 120 °C. Structural analyses revealed that RbF reacted readily with LiH to convert to RbH and LiF owing to the favorable thermodynamics during ball-milling. The newly generated RbH participated in the following dehydrogenation reaction, consequently resulting in a decrease in the reaction enthalpy change and activation energy.