Improved Hydrogen-Storage Thermodynamics and Kinetics for an RbF-Doped Mg(NH2)2-2LiH System

The introduction of RbF into the Mg(NH2)2-2LiH system significantly decreased its (de-)hydrogenation temperatures and enhanced its hydrogen-storage kinetics. The Mg(NH2)2-2LiH-0.08RbF composite exhibits the optimal hydrogen-storage properties as it could reversibly store approximately 4.76wt% hydrogen through a two-stage reaction with the onset temperatures of 80 degrees C for dehydrogenation and 55 degrees C for hydrogenation. At 130 degrees C, approximately 70% of hydrogen was rapidly released from the 0.08RbF-doped sample within 180min, and the fully dehydrogenated sample could absorb approximately 4.8wt% of hydrogen at 120 degrees 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.