Improvement of hydrogen storage property of three-component Mg(NH₂)₂–LiNH₂–LiH composites by additives

Abstract

The three-component Mg(NH₂)₂-LiNH₂-4LiH composite reversibly stores hydrogen exceeding 5 wt% at a temperature as low as 150 °C. In this work, a number of additives such as CeF₄, CeO₂, TiCl₃, TiH₂, NaH, KBH₄ and KH are added to the Mg(NH₂)₂-LiNH₂-4LiH composite in order to improve its kinetics, thermodynamics and cycling properties. Addition of 3 wt% of KH reduces the dehydrogenation onset temperature of the Mg(NH₂)₂-LiNH₂-4LiH composite to below 90 °C without emission of NH₃ during the whole dehydrogenation process up to 450 °C. Moreover, the dehydrogenation kinetics and cycling ability are remarkably enhanced upon KH-addition. The reaction model of the Mg(NH₂)₂-LiNH₂-4LiH composite is altered upon KH-addition with the active molecule density improved by about 200 times. In addition, by optimization of the ratio of Mg²⁺ to Li⁺ in the Mg(NH₂)₂-LiNH₂-LiH system, several novel composites, e.g., Mg(NH₂)₂-2LiNH₂-5.9LiH-0.1KH and Mg(NH₂)₂-LiNH₂-5.9LiH-0.1KH, with the hydrogen storage capacity exceeding 6 wt% without emission of NH₃ below 250 °C are developed. Our study demonstrates that there are various undiscovered candidates with promising hydrogen storage properties in the three-component Li-Mg-N-H system.