Recent development on hydrogen storage properties in metal–N–H systems

In this paper, we review our recent results on hydrogen storage properties in light metals(M)–nitrogen(N)–hydrogen(H) systems prepared by mechanochemical method. At first, the composite mixture of LiH and LiNH2 doped with TiCl3 as a catalyst was prepared by ball milling for 2 h under a H2 gas pressure of 1 MPa. The TDS profile indicated that ∼6 mass% H2 was desorbed by the reaction LiH + LiNH2 ↔ Li2NH + H2 in the temperature range from 150 to 250 °C under a He gas flow at a heating rate of 5 °C min−1, but the H-desorption equilibrium pressure PH2PH2 was ∼0.1 MPa at 250 °C. This temperature is too high for onboard use, indicating that further improvement is necessary to destabilize the above H-storage reaction. For that, we clarified the H-desorption mechanism by the isotopic exchange experiments, on the basis of which we designed a new Li–Mg–N–H composite system with the reaction 8LiH + 3Mg(NH2)2 ↔ 4Li2NH + Mg3N2 + 8H2. This composite materials desorbed ∼7 mass% H2 in the range from 120 to 200 °C and the H-desorption equilibrium pressure PH2PH2 was higher than 5 MPa at 200 °C, indicating that this system has an excellent potential for onboard applications.